Natural melatonin ''knockdown'' in C57BL/6J mice: rare mechanism truncates serotonin N-acetyltransferase

Resistance to the anabolic effects of growth hormone (GH) occurs with severe caloric deficit. This study examined whether moderate caloric deficit (50% of daily intake for 7 days) in the adolescent rat exceeds a critical threshold for GH action and whether a combination of GH and insulin-like growth factor I (IGF-I) would have enhanced anabolic effects on the diaphragm (Dia). Five groups of rats (4 wk old) were studied: 1) control (Ctl), 2) nutritionally deprived (ND), 3) ND + GH, 4) ND + IGF-I, and 5) ND + GH + IGF-I. IGF-I was given by continuous infusion (200 microg/day). GH was injected subcutaneously (250 microg every 12 h). Contractile and fatigue properties of the Dia were determined in vitro. Quantitative histochemical methods were used to determine Dia fiber type proportions, cross-sectional areas, and succinate dehydrogenase activities. The body weight of Ctl rats increased 46% compared with 7% in ND animals, whereas that of ND rats receiving growth factors was intermediate. Serum IGF-I levels were reduced 54% in ND animals and maintained with the provision of growth factors. Dia fatigue resistance was improved in ND animals receiving growth factors. There were no differences in Dia contractile properties, fiber type proportions, or succinate dehydrogenase activities across groups. ND resulted in atrophy/growth arrest of all Dia fibers (20-32%) compared with Ctl. Administration of IGF-I and/or GH completely prevented atrophy/growth arrest of all Dia fibers. No additive or synergistic effects were noted. We propose that these growth factors may provide useful short-term adjunctive nutritional support in circumstances in which the provision of optimal nutrition may be delayed or inadequate.     

Fat malabsorption in cystic fibrosis patients receiving enzyme replacement therapy is due to impaired intestinal uptake of long-chain fatty acids

BACKGROUND: Recombinant human growth hormone (GH) improves in vivo cardiac function in rats with postinfarction heart failure (MI). We examined the effects of growth hormone (14 days of 3.5 mg. kg-1. d-1 begun 4 weeks after MI) on contractile reserve in left ventricular myocytes from rats with chronic postinfarction heart failure. METHODS AND RESULTS: Cell shortening and [Ca2+]i were measured with the indicator fluo 3 in myocytes from MI, MI+GH, control, and normal animals treated with GH (C+GH) under stimulation at 0.5 Hz at 37 degrees C. Cell length was similar in MI and MI+GH rats (150+/-5 and 157+/-5 microm) and was greater in these groups than in the control and C+GH groups (140+/-4 and 139+/-4 microm, P<0.05). At baseline perfusate calcium of 1.2 mmol/L, myocyte fractional shortening and [Ca2+]i transients were similar among the 4 groups. We then assessed contractile reserve by measuring the increase in myocyte fractional shortening in the presence of high-perfusate calcium of 3.5 mmol/L. In the control and C+GH groups, myocyte fractional shortening and peak systolic [Ca2+]i were similarly increased in the presence of high-perfusate calcium. In the presence of high-perfusate calcium, both myocyte fractional shortening and peak systolic [Ca2+]i were depressed in the MI compared with the control groups. In contrast, myocyte fractional shortening (14.1+/-.9% versus 11.1+/-.9%, P<0.05) and peak systolic [Ca2+]i (647+/-43 versus 509+/-37 nmol/L, P<0.05) were significantly higher in MI+GH than in MI rats and were comparable to controls. Left ventricular myocyte expression of sarcoplasmic reticulum Ca2+ ATPase 2 (SERCA-2) and left ventricular SERCA-2 protein levels were increased in MI+GH compared with MI rats. CONCLUSIONS: Calcium-dependent contractile reserve is depressed in myocytes from rats with postinfarction heart failure. Long-term growth hormone therapy increases contractile reserve by restoring normal augmentation of systolic [Ca2+]i in myocytes from rats with postinfarction heart failure.     

Effects of muscle length on the response to unloading

Muscle mass, distribution of fiber types, fiber cross-sectional areas (CSA) and selected enzyme activities were determined in rats hindlimb-suspended free of immobilization (Susp-Free), suspended with the ankle dorsiflexed (Susp-DF, soleus stretched) or plantarflexed (Susp-PF, soleus shortened) for 10 days and compared to cage-control (Con) rats. Reduction of muscle weight associated with suspension was prevented in Susp-DF rats. The mean CSAs of slow fibers were Con = Susp-DF > Susp > PF > Susp-Free and of fast and intermediate fiber tended to be Susp-DF > Con > Susp-PF = Susp-Free. Mean activities of succinate dehydrogenase (SDH), alpha-glycerophosphate dehydrogenase (GPD) and myofibrillar adenosine triphosphatase (mATPase) in slow and fast fibers were similar in Con and Susp-Free rats. Mean SDH activity in slow fibers was higher in Susp-DF and Susp-PF than in Con and Susp-Free. No significant differences in SDH activities of fast fibers were observed among groups. GPD activity was higher in slow fibers of Susp-DF and Susp-PF compared to Con. The mATPase activity was higher in slow fibers of Susp-DF compared to Con and Susp-Free rats and lower in fast fibers of Susp-DF compared to Con rats. Thus, when compared to control, the patterns of adaptation were more similar in the Susp-DF and Susp-PF than in the Susp-Free. Although these results are consistent with previous studies demonstrating that the load placed on a muscle can affect protein metabolism, the direction and magnitude of the adaptive responses observed in the present study were closely associated with the chronically imposed changes in muscle length, i.e. fixed at either a shortened or a lengthened position.     

Effects of androgen administration on the growth hormone-insulin-like growth factor I axis in men with acquired immunodeficiency syndrome wasting

It is unknown whether hypogonadism contributes to decreased insulin-like growth factor I (IGF-I) production and/or how testosterone administration may effect the GH-IGF-I axis in human immunodeficiency virus (HIV)-infected men with the acquired immunodeficiency syndrome (AIDS) wasting syndrome (AWS). In this study, we investigate the GH-IGF-I axis in men with the AWS and determine the effects of testosterone on GH secretory dynamics, pulse characteristics determined from overnight frequent sampling, arginine stimulation, and total and free IGF-I levels. Baseline GH-IGF-I parameters in hypogonadal men with AWS (n=51) were compared before testosterone administration (300 mg, im, every 3 weeks vs. placebo for 6 months) with cross-sectional data obtained in two age-matched control groups: eugonadal men with AIDS wasting (n=10) and healthy age-matched normal men (n=15). The changes in GH-IGF-I parameters were then compared prospectively in testosterone- and placebo-treated patients. Mean overnight GH levels [1.8+/-0.3 and 2.4+/-0.3 vs. 0.90+/-0.1 microg/L (P=0.04 and P=0.003 vs. healthy controls)] and pulse frequency [0.35+/-0.06 and 0.37+/-0.02 vs. 0.22+/-0.03 pulses/h (P=0.06 and P=0.002 vs. healthy controls)] were comparably elevated in the eugonadal and hypogonadal HIV-positive groups, respectively, compared to those in the healthy control group. No significant differences in pulse amplitude, interpulse interval, or maximal GH stimulation to arginine administration (0.5 g/kg, i.v.) were seen between either the eugonadal and hypogonadal HIV-positive or healthy control patients. In contrast, IGF-I levels were comparably decreased in both HIV-positive groups compared to the healthy control group [143+/-16 and 165+/-14 vs. 216+/-14 microg/L (P=0.004 and P=0.02 vs. healthy controls)]. At baseline, before treatment with testosterone, overnight GH levels were inversely correlated with IGF-I (r=-0.42; P=0.003), percent ideal body weight (r=-0.36; P=0.012), albumin (r=-0.37; P=0.012), and fat mass (r=-0.52; P=0.0002), whereas IGF-I levels correlated with free testosterone (r=0.35; P=0.011) and caloric intake (r=0.32; P= 0.023) in the hypogonadal HIV-positive men. In a stepwise regression model, albumin (P=0.003) and testosterone (P=0.011) were the only significant predictors of GH [mean GH (microg/L)=-1.82 x albumin (g/dL) + 0.003 x total testosterone (microg/L) + 6.5], accounting for 49% of the variation in GH. Mean overnight GH levels decreased significantly in the testosterone-treated patients compared to those in the placebo-treated hypogonadal patients (0.9+/-0.3 vs. 0.2+/-0.4 microg/L; P=0.020). In contrast, no differences in IGF-I or free IGF-I were observed in response to testosterone administration. The decrement in mean overnight GH in response to testosterone treatment was inversely associated with increased fat-free mass (r=-0.49; P= 0.024), which was the only significant variable in a stepwise regression model for change in GH [change in mean GH (microg/L)=-0.197 x kg fat-free mass - 0.53] and accounted for 27% of the variation in the change in GH. In this study, we demonstrate increased basal GH secretion and pulse frequency in association with reduced IGF-I concentrations, consistent with GH resistance, among both hypogonadal and eugonadal men with AIDS wasting. Testosterone administration decreases GH in hypogonadal men with AIDS wasting. The change in GH is best predicted by and is inversely related to the magnitude of the change in lean body mass in response to testosterone administration. These data demonstrate that among hypogonadal men with the AWS, testosterone administration has a significant effect on the GH axis.     

Kallikrein gene expression in human pituitary tissues

Somatostatin has been suggested to influence the somatotrophic axis outside the central nervous system, in reducing GH-induced IGF-I mRNA and IGF-I generation. This study aimed to determine whether such effects were mediated via the GH receptor (GHR). GH-deficient dwarf rats aged 45-47 days (n = 8 per group) received twice daily subcutaneous injections of octreotide (1 mg/kg) (group O), saline (group S), octreotide (1 mg/kg) plus bovine GH (0.25 mg/kg) (group OG), or bovine GH (0.25 mg/kg) plus saline (group G) for 10 days. Octreotide-treated animals had less weight gain compared with saline-treated animals, but not when GH cotreated (group OG vs G). Octreotide had an overall effect on decreasing length gain (P < 0.01). Serum IGF-I (ng/ml) was reduced by octreotide (group O 171 +/- 11, group S 239 +/- 20, P < 0.01; group OG 283 +/- 30, group G 362 +/- 10, P < 0.001), as was serum insulin (P < 0.001). A significant decrease in hepatic and muscle IGF-I mRNA expression was found as expected, yet this was not associated with decreased hepatic GHR expression. Rather, an increase in hepatic 125I-bovine GH specific binding was observed (P < 0.001) and, in GH-cotreated animals (OG), hepatic GHR and GH binding protein (GHBP) mRNA expression were also increased by octreotide by approximately 40%. In muscle, octreotide was associated with an approximately 30% decrease in GHBP mRNA and no effect on GHR mRNA. This study suggests that the suppressive effects of octreotide on IGF-I metabolism, at least in liver, are not mediated via down-regulation of GHR expression, but more likely by direct effects on IGF-I expression.     

Immune responses to intestinal parasites: protection, pathology and prophylaxis

It has been suggested that adjunctive growth hormone (GH) therapy improves ovarian response and in vitro fertilization (IVF) outcome in specific groups of patients. The correlation between insulin-like growth factor (IGF) and GH is well established. The aim of this study was to determine whether changes in plasma GH correlate with IGF blood levels in patients during IVF treatment. Thirty-six women undergoing IVF and embryo transfer (ET) were examined. Ovarian stimulation was carried out by gonadotropin-releasing hormone agonists (GnRHa) and gonadotropins. Blood was drawn at the early and late follicular phase, on the day of human chorionic gonadotropin (hCG) injection and at the mid- and the late luteal phases. The samples were assayed for IGF-I, IGF-II, IGF-binding protein-3 (IGF BP-3), GH and estradiol. According to the IGF-I and GH plasma levels, patients were divided into three major groups: Group I consisted of patients in whom peak levels of GH reached more than 4 ng/ml and IGF-I decreased significantly. In this group, estradiol levels were 1863 +/- 149 pg/ml. Group II consisted of patients in whom peak blood GH levels did not exceed 2.5 ng/ml and the IGF-I level remained unchanged. In this group estradiol levels were 630 +/- 57 pg/ml. Group III consisted of patients in whom blood GH levels were low and remained unchanged while estradiol levels were 1600 +/- 420 pg/ml. In this group no significant increase in IGF-levels were observed. There was no significant change in the levels of either IGF-II or IGF BP-3 in any of the groups. We can conclude that (1) there is a negative correlation between GH and IGF-I plasma levels in patients undergoing controlled ovarian hyperstimulation (COH)-IVF, when levels of estradiol and GH are elevated; (2) plasma levels of IGF-I under ovarian hyperstimulation are probably regulated by a multifactorial system; and (3) no correlation was found between the plasma levels of IGF-I and those of IGF-II and IGF BP-3 in all patient groups.     

Normal growth hormone secretory reserve in men with idiopathic osteoporosis and reduced circulating levels of insulin-like growth factor-I

Many men with idiopathic osteoporosis have reduced circulating insulin-like growth factor-I (IGF-I) levels. The major source of circulating IGF-I is GH-mediated production by the liver. The known anabolic effects of GH on the skeleton raised the possibility of GH deficiency in these men. We sought to test this hypothesis in this study. Fourteen men (mean age, 52.1 +/- 3.2 yr, range 31-68) with idiopathic osteoporosis were studied. Mean lumbar spine bone mineral density (BMD) was 0.723 g/cm2, T score -3.5; femoral neck BMD was 0.642 g/cm2, T score, -3.07; distal (1/3) radius BMD was 0.708 g/cm2, T score, -2.05. Eleven of 14 (79%) had frank reductions in serum IGF-I levels compared with age and sex-matched values (158.5 +/- 50 SD vs. 180 +/- 45 SD). GH secretion was stimulated by iv arginine infusion (30 g) over 30 min followed 1 h later by oral L-dopa (500 mg). Serum GH was measured at time (t) = -15, 0, 30, 45, 60, 90, 120, 150, and 180 min. All patients responded to at least one stimulus with the majority (n = 9) responding to both. Five patients responded either to arginine or to L-dopa but not to both. Baseline GH for the entire group was 0.77 + 0.08 ng/mL (SEM). Peak GH following arginine (t = 45-60 min) was 14.0 +/- 2.8 ng/mL, a 17.7 +/- 2.8-fold rise. Peak GH following L-dopa (t = 120-180 min) was 5.7 +/- 1.0 ng/mL, a 9.2 +/- 2.2-fold rise. No difference in maximal secretion was observed between those with low or normal IGF-I levels. Neither IGF-I nor IGF binding protein-3 concentrations changed significantly during the short period of GH stimulation. These data suggest that men with osteoporosis and reduced IGF-I levels do not appear to have a deficiency in the GH axis. Other hormonal or local factors may be important in regulating IGF-I expression. Deficiencies of IGF-I production at skeletal sites may be important in the pathogenesis of this syndrome.     

Calculated magneto-optical Kerr effect in Fe, Co, and Ni

To examine whether GH and IGF-I participate in the regulation of obese (ob) mRNA expression we determined ob mRNA levels in epididydimal fat pads of hypophysectomised (hypox) rats, hypox rats treated with recombinant human (rh) GH or rhIGF-I and normal, weight-matched controls. We found that 1. ob mRNA was markedly suppressed after hypophysectomy (37 +/- 25% of controls), 2. GH infusion had no effect on ob mRNA, but stimulated IGF-I mRNA in fat pads, 3. IGF-I treatment further suppressed ob mRNA (3.5% +/- 0.6% of controls) and 4. serum insulin levels were decreased in all hypox groups (11.2 to 15.9% of controls). In conclusion, exogenous and GH-induced IGF-I differ in their effects on ob mRNA expression and GH is unable to restore ob mRNA towards normal at low insulin levels.     

The role of the growth hormone/insulin-like growth factor I axis in stimulation of protein synthesis in skeletal muscles following oral refeeding

The mechanisms behind stimulation of protein synthesis in skeletal muscles following oral feeding are not well understood. Previous research has not confirmed that insulin is a major factor behind this stimulation. In the present study we have used genetically altered mice, with either a lack of GH secretion due to a mutational gene inactivation [GH (-/-) dwarf, DW/JOrlBom-dw] or mice with a homozygous site-specific insertion mutation in the insulin-like growth factor-1 gene [IGF-I (m/m)], leading to a deficient IGF-I production. These gene knock-outs were used in comparison to their normal wild types for evaluation of the role that the GH/IGF-I axis may have in activation of nutritionally induced stimulation of protein synthesis in skeletal muscles during oral refeeding. Weight stable adult C57B16 mice served as an additional normal control group. Protein synthesis was measured by a modified flooding dose technique with radioactive L-[14C-U]phenylalanine incorporation into acid precipitated muscle proteins. Fractional protein synthesis in skeletal muscles after an overnight fast was comparable among C57B16 (0.076 +/- 0.009%/h), wild-type IGF-I(+/+) (0.061 +/- 0.008) and IGF-I(m/m) deficient mice (0.068 +/- 0.006%/h), whereas GH(-/-) incompetent mice had a lower fractional synthesis rate compared with GH(+/+) competent mice (0.045 +/- 0.006 vs. 0.068 +/- 0.007, P < 0.05). Refeeding with standard chow diet stimulated protein synthesis in muscles by more than 60% in all animal groups. This response was independent of circulating GH, total IGF-I concentrations in blood, as well as up-regulation of locally produced IGF-I messenger RNA (mRNA) in skeletal muscles.     

Uronic acid-containing glycosaminoglycans and keratan sulfate are present in the tectorial membrane of the inner ear: functional implications

The use of growth hormone (GH) as an anabolic agent is limited by its tendency to cause hyperglycemia and by its inability to reverse nitrogen wasting in some catabolic conditions. In a previous study comparing the anabolic actions of GH and IGF-I (insulin-like growth factor I), we observed that intravenous infusions of IGF-I (12 micrograms/kg ideal body wt [IBW]/h) attenuated nitrogen wasting to a degree comparable to GH given subcutaneously at a standard dose of 0.05 mg/kg IBW per d. IGF-I, however, had a tendency to cause hypoglycemia. In the present study, we treated seven calorically restricted (20 kcal/kg IBW per d) normal volunteers with a combination of GH and IGF-I (using the same doses as in the previous study) and compared its effects on anabolism and carbohydrate metabolism to treatment with IGF-I alone. The GH/IGF-I combination caused significantly greater nitrogen retention (262 +/- 43 mmol/d, mean +/- SD) compared to IGF-I alone (108 +/- 29 mmol/d; P < 0.001). GH/IGF-I treatment resulted in substantial urinary potassium conservation (34 +/- 3 mmol/d, mean +/- SE; P < 0.001), suggesting that most protein accretion occurred in muscle and connective tissue. GH attenuated the hypoglycemia induced by IGF-I as indicated by fewer hypoglycemic episodes and higher capillary blood glucose concentrations on GH/IGF-I (4.3 +/- 1.0 mmol/liter, mean +/- SD) compared to IGF-I alone (3.8 +/- 0.8 mmol/liter; P < 0.001). IGF-I caused a marked decline in C-peptide (1,165 +/- 341 pmol/liter; mean +/- SD) compared to the GH/IGF-I combination (2,280 +/- 612 pmol/liter; P < 0.001), suggesting maintenance of normal carbohydrate metabolism with the latter regimen. GH/IGF-I produced higher serum IGF-I concentrations (1,854 +/- 708 micrograms/liter; mean +/- SD) compared to IGF-I only treatment (1,092 +/- 503 micrograms/liter; P < 0.001). This observation was associated with increased concentrations of IGF binding protein 3 and acid-labile subunit on GH/IGF-I treatment and decreased concentrations on IGF-I alone. These results suggest that the combination of GH and IGF-I treatment is substantially more anabolic than either IGF-I or GH alone. GH/IGF-I treatment also attenuates the hypoglycemia caused by IGF-I alone. GH/IGF-I treatment could have important applications in diseases associated with catabolism.     

Arterial morphology and blood volumes of rats following 10-14 weeks of tail suspension

We hypothesized that the structure of systemic arteries would be altered following 10-14 wk of hindlimb unloading (tail suspension) in female Sprague-Dawley rats. Tail suspension resulted in atrophy of the soleus muscle (P < or = 0.01) but no significant differences in the mass of the extensor digitorum muscle, heart, or adrenal glands. In anesthetized rats, there was no difference between groups in arterial pressure (approximately 60 mm Hg). The corresponding maximal (topical papaverine) external diameter (ED) of femoral arteries (N = 5 per group) was reduced (P < or = 0.05) in tail suspended (TS, 511 +/- 47 microm, mean +/- SD) compared with cage sedentary (CS, 615 +/- 89 microm) and food restricted weight-paired (FR, 643 +/- 61 microm) groups. Neither hematocrit, red cell, plasma, nor total blood volume differed among groups. Following systemic vasodilation with papaverine, progressive arterial inflation with liquid silicon rubber (Microfil) revealed a reduction in both ED and distensibility of the femoral artery (P < or = 0.05). To determine the effects of tail suspension on systemic arterial morphology, the vasculature of additional rats was perfusion fixed at 80 mm Hg during vasodilation. Cross sections (thickness, 8 microm) of the carotid, axillary, iliac, and femoral arteries were then evaluated. Whereas the internal diameter of femoral arteries was smaller in TS than in CS (P < 0.05), no differences were observed for other vessels among groups. Further, arterial wall thickness increased systemically (overall, P < 0.05; carotid, 24%, P < 0.01; femoral, 28%, P < 0.01) following tail suspension. These findings illustrate adaptation in the structure of conduit arteries to prolonged tail suspension, with diameter altered regionally and wall thickness increased systemically. We suggest that chronic changes in activity patterns can influence arterial structure.     

Hemodynamic characterization of YM435, a novel dopamine DA1 receptor agonist, in anesthetized dogs

In previous studies on experimental renal failure, hypertrophy of cardiomyocytes, diminished capillarization, and increased intercapillary distances had been observed, abnormalities that will expose the heart to reduced ischemia tolerance. It has not been established, however, whether such structural alterations are unique for the heart (eg, as a consequence of left ventricular hypertrophy) or are demonstrable in other tissues as well. Clarification of this point is important to test hypotheses on some potential mechanisms for cardiac undercapillarization. To address this issue further, we compared capillary length density (by stereologic techniques) in perfusion-fixed skeletal muscle (m. psoas) and hearts of subtotally nephrectomized (SNX) rats with moderate renal failure to those in sham-operated pair-fed controls. The duration of renal failure was 8 weeks. SNX rats had significantly higher mean systolic blood pressure (128 mm Hg v 109 mm Hg), serum creatinine, and urea levels. Despite pair feeding, the mean body weight was significantly lower in the SNX rats (409 g v 471 g), but the left ventricular weight to body weight ratio tended to be higher than in the sham-operated controls (2.39 mg/g v 2.13 mg/g). In the heart, myocyte mean cross-sectional area (675 +/- 112 microm2 v 545 +/- 111 microm2) and volume density of nonvascular interstitial tissue (3.47 +/- 1.04 v 1.33 +/- 0.22) were significantly higher in the SNX rats than in the controls. In parallel, myocardial capillary length density was significantly reduced after subtotal nephrectomy (3,036 +/- 535 mm/mm3 v 3,916 +/- 615 mm/mm3). In contrast, in skeletal muscle, myocyte cross-sectional area (3,109 +/- 783 microm2 v 3,042 +/- 639 microm2), capillary length density (718 +/- 248 mm/mm3 v 717 +/- 184 mm/mm3), and three-dimensional capillary fiber ratio (2.10 +/- 0.26 v 2.13 +/- 0.4) were similar in SNX and control rats. These data document a selective defect of capillarization in the heart of animals with moderate renal failure, pointing to tissue-specific abnormalities of cardiac capillarogenesis.     

Evaluation of disease status with sensitive measures of growth hormone secretion in 60 postoperative patients with acromegaly

Traditionally, suppression of GH measured by polyclonal RIA to less than 2.0 microg/L after oral glucose was accepted as evidence of remission after transsphenoidal surgery for acromegaly. Recently, with newer, more sensitive GH assays, a cut-off of less than 1.0 microg/L has been suggested. With the development of accurate insulin-like growth factor I (IGF-I) and IGF-binding protein-3 (IGFBP-3) assays, additional tools are now available for assessing postoperative GH secretion. There has, however, never been a systematic comparison of sensitive GH, IGF-I, and IGFBP-3 assays in defining disease status in a large cohort of postoperative patients with acromegaly. Therefore, we evaluated how the use of modern assays impacts on our assessment of disease activity in these patients. Sixty postoperative subjects with acromegaly and 25 age-matched healthy subjects were evaluated with nadir GH levels after 100 g oral glucose as well as baseline IGF-I and IGFBP-3 levels. GH was assayed by polyclonal RIA, sensitive immunoradiometric assay (IRMA), and highly sensitive enzyme-linked immunosorbent assay. The mean nadir GH determined by IRMA was 0.09 +/- 0.004 microg/L in the healthy subjects, with the upper limit of the normal nadir being 0.14 microg/L (mean + 2 SD). Subjects with acromegaly were divided into those with active disease (n = 22), defined by elevated IGF-I levels, and those in remission (n = 38), defined by normal IGF-I levels. GH determined by IRMA failed to suppress into the normal range defined by our healthy subjects in all patients with active disease; nadir GH determined by IRMA ranged from 0.33-5.0 microg/L in this group. In 50% of the active group, nadir GH levels determined by IRMA were less than 1.0 microg/L, a GH nadir previously considered normal by strict criteria. When nadir GH levels in the subjects with active disease were measured by polyclonal RIA, there was overlap with the range of RIA values in the healthy subjects. Thus, the IRMA was superior to the RIA in that the overlap between these two groups was eliminated. Subjects with acromegaly in remission included those with normal GH suppression (n = 23; mean nadir GH by IRMA, 0.10 +/- 0.006 microg/L) and others with abnormal GH suppression by IRMA (n = 15; mean nadir GH by IRMA, 0.35 +/- 0.07 microg/L). The latter group may have persistent GH dysregulation detected by the sensitive IRMA. GH levels measured by enzyme-linked immunosorbent assay confirmed the IRMA results. IGFBP-3 levels were significantly higher in subjects with active acromegaly (4940 +/- 301 microg/L) vs. those in healthy subjects (2887 +/- 153 microg/L; P < 0.0001) and those in the subjects in remission (2966 microg/L; P < 0.0001). IGFBP-3 levels correlated overall with IGF-I levels (r = 0.765; P < 0.0001), but IGFBP-3 levels were not predictive of disease status because 32% of the subjects with active acromegaly had normal IGFBP-3 levels. In addition, failure of GH to suppress adequately was not associated with a higher IGFBP-3 level among the subjects in remission. These data indicate that the IRMA is superior to the RIA in distinguishing between patients with active disease (defined by elevated IGF-I levels) and healthy subjects. We also show that GH levels after oral glucose measured with highly sensitive GH assays can be much lower in subjects with active disease than previously believed; values less than 1.0 microg/L may be found in up to 50% of patients. In addition, in 39% of patients in apparent remission with normal IGF-I levels, GH determined by highly sensitive assays fails to suppress normally; it remains to be determined whether these patients are at higher risk for recurrence of active disease.     

Effect of reactive oxygen species on K+ contractures in the rat diaphragm

Reactive oxygen species (ROS) are postulated to alter low-frequency contractility of the unfatigued and fatigued diaphragm. It has been proposed that ROS affect contractility through changes in membrane excitability and excitation-contraction coupling. If this hypothesis is true, then ROS should alter depolarization-dependent K+ contractures. Xanthine oxidase (0.01 U/ml) + hypoxanthine (1 mM) were used as a source of superoxide anion eliciting oxidative stress on diaphragm fiber bundles in vitro. Diaphragm fiber bundles from 4-mo-old Fischer 344 rats were extracted and immediately placed in Krebs solution bubbled with 95% O2-5% CO2. After 10 min of equilibration, a K+ contracture (Pre; 135 mM KCl) was induced. Fiber bundles were assigned to the following treatment groups: normal Krebs-Ringer (KR; Con) and the xanthine oxidase system (XO) in KR solution. After 15 min of treatment exposure, a second (Post) K+ contracture was elicited. Mean time-to-peak tension for contractures was significantly decreased in Post vs. Pre (16.0 +/- 0.7 vs. 19.8 +/- 1.0 s) with XO; no change was noted with Con. Furthermore, peak contracture tension was significantly higher (31.5%) in the XO group Post compared with Pre; again, no significant change was found with KR. The relaxation phase was also altered with XO but not with KR. Additional experiments were conducted with application of 1 mM hypoxanthine, with results similar to the Con group. We conclude that the application of ROS altered the dynamics of K+ contractures in the rat diaphragm, indicating changes in voltage-dependent excitation-contraction coupling.     

Effects of insulin-like growth factor I combined with growth hormone on glucocorticoid-induced whole-body protein catabolism in man

Treatment with insulin-like growth factor I (IGF-I) alone failed to affect glucocorticoid-induced protein catabolism in a previous study from our laboratory. To assess the effects of the combination of IGF-I and GH in a similar protocol, 24 normal subjects received (in a double-blind, randomized, placebo-controlled manner) s.c. injections of either GH alone (0.3 IU/kg.day), the combination of IGF-I (80 micrograms/kg.day) and GH (0.3 IU/kg.day), or placebo for a period of 6 days during which they were treated with methylprednisolone (0.5 mg/kg.day). Whole-body protein kinetics measured, using the [1-13C]-leucine infusion technique, demonstrated that leucine flux (a parameter of protein breakdown) increased during administration of glucocorticoids alone (placebo group) and during GH-treatment, whereas the glucocorticoid-induced increase was abolished during IGF-I plus GH (P < 0.03 vs. GH). Leucine oxidation (a parameter of irreversible protein catabolism) increased in the placebo group (+60 +/- 14.5%, P < 0.005, day 7 vs. day 1), remained unchanged in the GH group (+2.5 +/- 10%), and decreased in the combination group (-17.7 +/- 3.3%, P < 0.002, day 7 vs. day 1). Glucose MCR decreased in the group receiving placebo (P < 0.05) and remained unchanged during combined treatment with IGF-I plus GH. It is concluded that glucocorticoid-induced protein, catabolism (leucine oxidation) is abolished during coadministration of GH (anticatabolic effect), whereas treatment with IGF-I and GH results in a net anabolic effect without adverse effects on peripheral glucose clearance.     

Experimental diabetic renal growth: role of growth hormone and insulin-like growth factor-I

We have compared the kidneys of two inbred strains of rats (Lewis and Lewis-Dwarf) 7 days after the induction of diabetes mellitus with streptozotocin, in order to examine the influence of a selective growth hormone (GH) deficiency on diabetic renal growth and insulin-like growth factor-I (IGF-I) content of the kidneys. Insulin-like growth factor-I (IGF-I) content of the kidneys. Insulin-like growth factor-I was measured by radioimmunoassay and its distribution within the kidney by immunohistochemical staining. We detected a significant increase in both the wet weight (32.9 +/- 5.3%, P = 0.0085) and dry weight (16.3 +/- 6.3%, P = 0.046) of the kidneys of diabetic Lewis rats but dwarf rats, selectively deficient in GH, did not show a significant increase in either parameter. Extractable IGF-I increased within the kidneys of diabetic rats of both strains but to a lesser extent in the dwarf rats (+105 +/- 28% and +65 +/- 21% respectively, P < 0.01). In diabetic Lewis rats a positive correlation was noted between the severity of glycaemia and kidney IGF-I content (r = 0.604, P < 0.05) but no such correlation was noted in dwarf rats. Inulin-like growth factor-I immunostaining increased in diabetic rats of both strains, mainly within cells of the thick ascending limb of the loop of Henle including damaged and vacuolated cells. However, morphometric analysis of the staining showed that it was significantly less widespread in the diabetic dwarf rats (P = 0.026).(ABSTRACT TRUNCATED AT 250 WORDS)     

Muscle unloading induces slow to fast transitions in myofibrillar but not mitochondrial properties. Relevance to skeletal muscle abnormalities in heart failure

Muscle deconditioning is a common observation in patients with congestive heart failure (CHF), chronic obstructive pulmonary disease, neuromuscular diseases or prolonged bed rest. To gain further insight into metabolic and mechanical properties of deconditioned slow-twitch (soleus) or fast-twitch (EDL) skeletal muscles, we induced experimental muscle deconditioning by hindlimb suspension (HS) in rats for 3 weeks. Cardiac muscle was also studied. Besides profound muscle atrophy, increased proportion of fast type II fibers as well as fast myosin isoenzymes, we found decreased calcium sensitivity of Triton X-100 skinned fiber bundles of soleus muscle directed towards the fast muscle phenotype. Glycolytic enzymes such as hexokinase and pyruvate kinase were increased, and the LDH isoenzyme pattern was clearly shifted from an oxidative to an anaerobic profile. Creatine kinase (CK) and myokinase activities were increased in HS soleus towards EDL values. Moreover, the M-CK mRNA level was greatly increased in soleus, with no change in EDL. However, oxygen consumption rate assessed in situ in saponin skinned fibers (12.5 +/- 0.8 in C and 15.1 +/- 0.9 micromol O2/min/g dw in HS soleus compared to 7.3 +/- 1.3 micromol O2/min/g dw in control EDL), as well as mitochondrial CK (mi-CK) and citrate synthase activities, were preserved in HS soleus. Following deconditioning no change in Km for ADP of mitochondrial respiration, either in the absence (511 +/- 92 in C and 511 +/- 111 microM in HS soleus compared to 9 +/- 4 microM in control EDL) or presence of creatine (88 +/- 10 in C and 95 +/- 16 microM in HS soleus compared to 32 +/- 9 microM in control EDL), was found. The results show that muscle deconditioning induces a biochemical and functional slow to fast phenotype transition in myofibrillar and cytosolic compartments of postural muscle, but not in the mitochondrial compartment, suggesting that these compartments are differently regulated under conditions of decreased activity.     

Influence of chronic Naltrexone treatment on growth hormone and insulin secretion in obese subjects

OBJECTIVE: Recent studies have demonstrated the restoration of a normal 24 h GH profile induced by a reduction of insulinaemia after weight loss, suggesting a reciprocal relationship between plasma insulin and GH concentrations. We aimed to clarify if an opiate-induced reduction in plasma insulin could affect GH secretion in obesity. DESIGN: We have studied the insulin response to an oral glucose tolerance test (OGTT) and the GH response to GHRH before and after prolonged treatment with Naltrexone (NTX). C-peptide, IGF-I, IGFBP-3 plasma levels and the IGF-I/IGFBP-3 molar ratio were also determined. SUBJECTS: Twelve obese women (aged 25-41 y; Body mass index (BMI): 31-39 kg/m2) and six lean normal women (aged 25-38; BMI: 19.8-23.1 kg/m2). MEASUREMENT: GH was determined by the IRMA method; insulin, C-peptide, IGF-I and IGFBP-3 were assayed by the RIA method. For molar comparison between IGF-I and IGFBP-3 we have considered 30.5 kDa the molar weight of IGFBP-3. Results are expressed as mean +/- s.e.m. RESULTS: We observed a significant decrease in basal concentration of both insulin (230.1 +/- 34.9 vs 133.2 +/- 16.9 pmol/L; P < 0.005) and C-peptide (3.7 +/- 0.3 vs 2.4 +/- 0.1 micrograms/L; P < 0.02). No modifications in the insulin secretory response to the OGTT were observed. A significant increase of the GHRH-induced GH peak response (7.7 +/- 1.4 vs 19.7 +/- 3.1 micrograms/L; P < 0.01) and GH-AUC (533 +/- 151 vs 1415 +/- 339 micrograms/L/120 min; P < 0.01) was found after NTX treatment. A negative correlation was found between basal insulin and GH peak values, both before (r = -0.641, P = 0.027) and after NTX (r = -0.714, P = 0.013). No modifications were found in IGF-I, IGFBP-3 and IGF-I/IGFBP-3 molar ratio. Moreover, NTX affected neither the insulin response to OGTT or IGF-I, IGFBP-3 and IGF-I/IGFBP-3 molar ratio in a group of six lean controls. Conversely, NTX significantly reduced the GH response to GHRH, when expressed as both peak and AUC values. CONCLUSIONS: The opiate antagonist significantly reduced basal insulin concentrations and augmented the GH response to GHRH in obese subjects. In the absence of modifications in IGF-I and IGFBP-3 plasma levels and their molar ratio, we propose that insulin may exert a negative feedback on GH secretion.