Hypothalamic/pituitary-axis of the spontaneous dwarf rat: autofeedback regulation of growth hormone (GH) includes suppression of GH releasing-hormone receptor messenger ribonucleic acid

In this study, the spontaneous dwarf rat (SDR) has been used to examine GHRH production and action in the selective absence of endogenous GH. This dwarf model is unique in that GH is not produced because of a point mutation in the GH gene. However, other pituitary hormones are not obviously compromised. Examination of the hypothalamic pituitary-axis of SDRs revealed that GHRH messenger RNA (mRNA) levels were increased, whereas somatostatin (SS) and neuropeptide Y (NPY) mRNA levels were decreased, compared with age- and sex-matched normal controls, as determined by Northern blot analysis (n = 5 animals/group; P < 0.05). The elevated levels of GHRH mRNA in the SDR hypothalamus were accompanied by a 56% increase in pituitary GHRH receptor (GHRH-R) mRNA, as determined by RT-PCR (P < 0.05). To investigate whether the up-regulation of GHRH-R mRNA resulted in an increase in GHRH-R function, SDR and control pituitary cell cultures were challenged with GHRH (0.001-10 nM; 15 min), and intracellular cAMP concentrations were measured by RIA. Interestingly, SDR pituitary cells were hyperresponsive to 1 and 10 nM GHRH, which induced a rise in intracellular cAMP concentrations 50% greater than that observed in control cultures (n = 3 separate experiments; P < 0.05 and P < 0.01, respectively). Replacement of GH, by osmotic minipump (10 microg/h for 72 h), resulted in the suppression of GHRH mRNA levels (P < 0.01), whereas SS and NPY mRNA levels were increased (P < 0.05), compared with vehicle-treated controls (n = 5 animals/treatment group). Consonant with the fall in hypothalamic GHRH mRNA was a decrease in pituitary GHRH-R mRNA levels. Although replacement of insulin-like growth factor-I (IGF-I), by osmotic pump (5 microg/h for 72 h), resulted in a rise in circulating IGF-I concentrations comparable with that observed after GH replacement, IGF-I treatment was ineffective in modulating GHRH, SS, or NPY mRNA levels. However, IGF-I treatment did reduce pituitary GHRH-R mRNA levels, compared with vehicle-treated controls (P < 0.05). These results further validate the role of GH as a negative regulator of hypothalamic GHRH expression, and they suggest that SS and NPY act as intermediaries in GH-induced suppression of hypothalamic GHRH synthesis. These data also demonstrate that increases in circulating IGF-I are not responsible for changes in hypothalamic function observed after GH treatment. Finally, this report establishes modulation of GHRH-R synthesis as a component of GH autofeedback regulation.     

Adrenocorticotropic hormone therapy for infantile spasms alters pyruvate metabolism in the central nervous system

Growth hormone secretagogues (GHSs) are synthetic peptidyl and nonpeptidyl compounds that are believed to stimulate the release of GH by a direct effect on the pituitary somatotrope and by stimulation of growth hormone-releasing hormone (GHRH) release and the suppression of somatostatin (SRIH) tone. Recently, the receptor for these pharmacologic agents was cloned and its expression localized to the pituitary and hypothalamus. The elucidation of an unique GHS receptor (GHS-R) suggests there is a yet to be identified endogenous ligand which could exert an important role in regulation of GH secretion. It is clearly established that GH acts to regulate its own production by feeding back at the level of the hypothalamus to downregulate GHRH and upregulate SRIH synthesis and by induction of IGF-I, which acts at the pituitary to block somatotrope responsiveness to GHRH. If the endogenous GHS/GHS-R signaling system is important in regulating GH release, it might be reasoned that changes in circulating GH concentrations would also directly or indirectly (via generation of IGF-I) modify GHS-R production. To test this hypothesis we used RT-PCR to examined pituitary and hypothalamic GHS-R mRNA levels in the spontaneous dwarf rat (SDR), an animal model characterized by the absence of GH due to a point mutation in the GH gene. In the absence of GH feedback regulation, SDR pituitary GHS-R mRNA levels were 385 +/- 61% greater (p < 0.01) than those observed in normal controls while SDR hypothalamic GHS-R mRNA levels were not significantly different from those in normal rats. Three-day subcutaneous infusion of rat GH by osmotic pump reduced SDR pituitary GHS-R mRNA levels to 55 +/- 9% of vehicle-treated controls (p < 0.05) but did not significantly alter hypothalamic GHS-R mRNA levels. To test if the changes in GHS-R mRNA levels observed following GH treatment were due to elevation of circulating IGF-I concentrations, SDRs were infused with recombinant human IGF-I. Replacement of IGF-I did not significantly alter either pituitary or hypothalamic GHS-R mRNA levels, indicating that GH acts independent of circulating IGF-I to regulate pituitary GHS-R expression in the SDR model.     

Phenotype and genetic analysis of a syndrome caused by an inactivating mutation in the growth hormone-releasing hormone receptor: Dwarfism of Sindh

We report, in detail, a new form of familial dwarfism, including its phenotypic features, hormonal profile, and molecular basis. Following a newspaper report of severe dwarfism in two villages in the province of Sindh, Pakistan, we organized an expedition to study its clinical, genetic, and molecular characteristics. We identified 18 dwarfs (15 male, 3 female), all members of a consanguineous kindred, ranging in age from newborn to 28 yr. Mean height was 7.2 SD below the norm, with mean adult heights of 130 cm for males and 113.5 cm for females. Body proportions and habitus were normal; but head circumference was 4.1 SD, and blood pressure approximately 3 SD below the norm. There was no dysmorphism, no microphallus, and no history of hypoglycemia. Serum GH did not respond to provocative stimuli (GHRH, L-dopa, or clonidine). Insulin-like growth factor I (IGF-I) and IGF-binding protein 3 were low (5.2 +/- 2.0 ng/mL and 0.42 +/- 0.13 microg/mL, respectively; mean +/- SD) but rose normally with GH treatment. One affected, dwarfed couple had a son, demonstrating fertility in both sexes. Clinical and endocrinological evidence suggested isolated GH deficiency with a recessive inheritance pattern. The GH-N gene was found to be intact. Linkage analysis of microsatellite chromosomal markers near other candidate genes yielded a high LOD score (6.26) for the GHRH receptor (GHRH-R) locus. DNA sequencing revealed a nonsense mutation (Glu50-->Stop) in the extracellular domain of the GHRH-R. This mutation predicts a severely truncated GHRH-R; it is identical to that recently reported in four patients from two other families. Inheritance is autosomal recessive (chromosome 7p) with a high degree of penetrance. Relatives heterozygous for the mutation had moderately decreased IGF-I levels and slightly blunted GH responses to GHRH and L-dopa, but they showed only minimal or no height deficit. This syndrome represents the human homologue of the little (lit/lit) mouse and closely resembles its phenotype. It demonstrates the absolute requirement of GHRH signaling for pituitary GH secretion and postnatal growth in humans, and its relatively minor (but discernible) biological importance in extrapituitary sites. The syndrome is distinct from other forms of GH deficiency with respect to microcephaly, asymptomatic hypotension, and absence of features such as facial dysplasia, significant truncal obesity, microphallus, or hypoglycemia. Its discovery raises the possibility of milder mutations in the GHRH-R gene as potential causes for partial GH insufficiency and idiopathic short stature.     

CpG islands in chromatin organization and gene expression

Twelve female rats weighing approximately 150 g received in the submaxillary gland a pellet capable of releasing 3.5 microg GHRH/h for 60 days. Another eight sex- and weight-matched animals received placebo pellets in the same place. After two months the animals were killed, heart blood was collected and pituitary and submaxillary glands were carefully dissected. Pituitary GH content in both placebo- and GHRH-treated animals showed similar values, but plasma GH and IGF-I levels were significantly lower in the animals carrying GHRH pellets (P<0.03); these animals also had a significantly higher GH content in the submaxillary gland (19.2+/-8 ng/mg protein) compared with the placebo-treated group (1.1+/-0.3 ng/mg protein). GH mRNA was present only in the submaxillary gland of GHRH-treated rats as determined by PCR-Southern blot and by in situ hybridization methods. It is concluded that high local GHRH levels are capable of inducing transdifferentiation in submaxillary gland cells to synthesize GH.     

"Born from the flank"--discussion concerning "cesarean section" in animals in the Talmud

We determined growth hormone (GH) and insulin-like growth factor I (IGF-I) levels after a 3 h infusion of escalating doses of growth hormone-releasing hormone (GHRH(1-29)) followed by a bolus injection in hypopituitary patients with marked differences in pituitary features at magnetic resonance imaging (MRI) in order to evaluate further the contribution of MRI in the definition of pituitary GH reserve in GH-deficient patients. Twenty-nine patients (mean age 14.5 +/- 4.0 years) were studied. Group I comprised 13 patients: seven with isolated GH deficiency (IGHD) (group Ia) and six with multiple pituitary hormone deficiency (MPHD) (group Ib) who had anterior pituitary hypoplasia, unidentified pituitary stalk and ectopic posterior pituitary at MRI, Group II consisted of eight patients with IGHD and small anterior pituitary/empty sella, while in group III eight had IGHD and normal morphology of the pituitary gland. Growth hormone and IGF-I levels were measured during saline infusion at 08.30-09.00 h, as well as after infusion of GHRH (1-29) at escalating doses for 3h: 0.2 micrograms/kg at 09.00-10.00 h, 0.4 micrograms/kg at 10.00-11.00 h, 0.6 micrograms/kg at 11.00-12.00 h and an intravenous bolus of 2 micrograms/ kg at 12.00 h. In the group I patients, the peak GH response to GHRH(1-29) was delayed (135-180 min) and extremely low (median 2mU/l). In group II it was delayed (135-180 min), high (median 34.8 mU/l) and persistent (median 37.4 mU/l at 185-210 min). In group III the peak response was high (median 30.8 mU/l) and relatively early (75-120 min) but it declined rapidly (median 14.4 mU/l at 185-210 min). In one group I patient, GH response increased to 34.6 mU/l. The mean basal value of IGF-I levels was significantly lower in group I (0.23 +/- 0.05 U/ml) than in groups II (0.39 +/- 0.13U/ ml, p < 0.01) and III (1.54 +/- 0.46 U/ml, p < 0.001) and did not vary significantly during the GHRH(1-29) infusion. The present study demonstrates that the impaired GH response to 3 h of continuous infusion of escalating doses of GHRH(1-29) was strikingly indicative for pituitary stalk abnormality, strengthening the case for use of GHRH in the differential diagnosis of GH deficiency. The low GH response, more severe in MPHD patients, might be dependent on the residual somatotrope cells, while the better response (34.6 mU/l) in the group Ia patients might suggest that prolonged GHRH infusion could help in evaluating the amount of residual GH pituitary tissue. Pituitary GH reserve, given the GH response to GHRH infusion in GH-deficient patients with small anterior pituitary/empty sella, seems to be maintained.     

Ipamorelin, the first selective growth hormone secretagogue

The development and pharmacology of a new potent growth hormone (GH) secretagogue, ipamorelin, is described. Ipamorelin is a pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2), which displays high GH releasing potency and efficacy in vitro and in vivo. As an outcome of a major chemistry programme, ipamorelin was identified within a series of compounds lacking the central dipeptide Ala-Trp of growth hormone-releasing peptide (GHRP)-1. In vitro, ipamorelin released GH from primary rat pituitary cells with a potency and efficacy similar to GHRP-6 (ECs) = 1.3+/-0.4nmol/l and Emax = 85+/-5% vs 2.2+/-0.3nmol/l and 100%). A pharmacological profiling using GHRP and growth hormone-releasing hormone (GHRH) antagonists clearly demonstrated that ipamorelin, like GHRP-6, stimulates GH release via a GHRP-like receptor. In pentobarbital anaesthetised rats, ipamorelin released GH with a potency and efficacy comparable to GHRP-6 (ED50 = 80+/-42nmol/kg and Emax = 1545+/-250ng GH/ml vs 115+/-36nmol/kg and 1167+/-120ng GH/ml). In conscious swine, ipamorelin released GH with an ED50 = 2.3+/-0.03 nmol/kg and an Emax = 65+/-0.2 ng GH/ml plasma. Again, this was very similar to GHRP-6 (ED50 = 3.9+/-1.4 nmol/kg and Emax = 74+/-7ng GH/ml plasma). GHRP-2 displayed higher potency but lower efficacy (ED50 = 0.6 nmol/kg and Emax = 56+/-6 ng GH/ml plasma). The specificity for GH release was studied in swine. None of the GH secretagogues tested affected FSH, LH, PRL or TSH plasma levels. Administration of both GHRP-6 and GHRP-2 resulted in increased plasma levels of ACTH and cortisol. Very surprisingly, ipamorelin did not release ACTH or cortisol in levels significantly different from those observed following GHRH stimulation. This lack of effect on ACTH and cortisol plasma levels was evident even at doses more than 200-fold higher than the ED50 for GH release. In conclusion, ipamorelin is the first GHRP-receptor agonist with a selectivity for GH release similar to that displayed by GHRH. The specificity of ipamorelin makes this compound a very interesting candidate for future clinical development.     

Evidence for a role for the cyclic adenosine 3',5'-monophosphate/protein kinase-A pathway in regulation of the gonadotropin subunit messenger ribonucleic acids

cAMP regulation of gonadotropin secretion and subunit mRNA levels was studied in pituitary cells perifused with pulses of GnRH. Pituitary cells from 7-week-old male rats castrated at 5 weeks of age were stimulated hourly for 9-24 h with 1-min pulses of GnRH, the adenylate cyclase activator forskolin, the cell-permeable cAMP analog 8-bromo-cAMP (8Br-cAMP), or control medium. Cells were also treated with the nonsteroidal antiinflammatory drug flufenamic acid, which reduces pituitary cAMP levels. During perifusion, the effluent was collected in 10-min fractions for FSH and LH assay. At the completion of perifusion, total RNA was extracted, and gonadotropin subunit mRNA levels were quantitated by Northern analysis. Continuous administration of flufenamic acid gradually reduced the amplitude of GnRH-stimulated FSH and LH pulses to nadir values of 40 +/- 4.7% and 62 +/- 12% of the control value, respectively. Flufenamic acid decreased (P < 0.05) FSH beta and alpha-subunit mRNA levels and blocked the effect of GnRH to lengthen LH beta mRNA. Pulses of forskolin or 8Br-cAMP released LH and FSH, and continuous forskolin or 8Br-cAMP potentiated the gonadotropin stimulatory effect of GnRH. Forskolin or 8Br-cAMP increased (P < 0.05) FSH beta mRNA and alpha-subunit mRNA levels when administered in pulses, but not when administered continuously, and lengthened LH beta mRNA. The Nal-Glu GnRH antagonist blocked the effects of GnRH pulses, but not the effects of 8Br-cAMP or forskolin. In conclusion, lowering intracellular cAMP levels with flufenamic acid attenuated GnRH-stimulated gonadotropin secretion, decreased alpha-subunit and FSH beta mRNA levels, and blocked the effect of GnRH to lengthen LH beta mRNA, whereas 8Br-cAMP or forskolin produced the opposite effect. These data extend previous results which suggested that cAMP modulates gonadotropin secretion and indicate that the cAMP/A-kinase pathway regulates each of the gonadotropin subunit mRNAs.     

Blur and contrast as pictorial depth cues

OBJECTIVE: Infusion of GH secretagogues appears to be a novel endocrine approach to reverse the catabolic state of critical illness, through amplification of the endogenously blunted GH secretion associated with a substantial IGF-I rise. Here we report the dynamic characteristics of spontaneous nightly TSH and PRL secretion during prolonged critical illness, together with the concomitant effects exerted by the administration of GH-secretagogues, GH-releasing hormone (GHRH) and GH-releasing peptide-2 (GHRP-2) in particular, on night-time TSH and PRL secretion. PATIENTS AND DESIGN: Twenty-six critically ill adults (mean +/- SEM age: 63 +/- 2 years) were studied during two consecutive nights (2100-0600 h). According to a weighed randomization, they received 1 of 4 combinations of infusions, within a randomized, cross-over design for each combination: placebo (one night) and GHRH (the next night) (n = 4); placebo and GHRP-2 (n = 10); GHRH and GHRP-2 (n = 6); GHRP-2 and GHRH + GHRP-2 (n = 6). Peptide infusions (duration 21 hours) were started after a bolus of 1 microgram/kg at 0900 h and infused (1 microgram/kg/h) until 0600 h. MEASUREMENTS: Serum concentrations of TSH and PRL were determined by IRMA every 20 minutes and T4, T3 and rT3 by RIA at 2100 h and 0600 h in each study night. Hormone secretion was quantified using deconvolution analysis. RESULTS: During prolonged critical illness, mean night-time serum concentrations of TSH (1.25 +/- 0.42 mlU/l) and PRL (9.4 +/- 0.9 micrograms/l) were low-normal. However, the proportion of TSH and PRL that was released in a pulsatile fashion was low (32 +/- 6% and 16 +/- 2.6%) and no nocturnal TSH or PRL surges were observed. The serum levels of T3 (0.64 +/- 0.06 nmol/l) were low and were positively related to the number of TSH bursts (R2 = 0.32; P = 0.03) and to the log of pulsatile TSH production (R2 = 0.34; P = 0.03). GHRP-2 infusion further reduced the proportion of TSH released in a pulsatile fashion to half that during placebo infusion (P = 0.02), without altering mean TSH levels. GHRH infusion increased mean TSH levels and pulsatile TSH production, 2-fold compared to placebo (P = 0.03) and 3-fold compared to GHRP-2 (P = 0.008). The addition of GHRP-2 to GHRH infusion abolished the stimulatory effect of GHRH on pulsatile TSH secretion. GHRP-2 infusion induced a small increase in mean PRL levels (21%; P = 0.02) and basal PRL secretion rate (49%; P = 0.02) compared to placebo, as did GHRH and GHRH + GHRP-2. CONCLUSIONS: The characterization of the specific pattern of anterior pituitary function during prolonged critical illness is herewith extended to the dynamics of TSH and PRL secretion: mean serum levels are low-normal, no noctumal surge is observed and the pulsatile fractions of TSH and PRL release are reduced, as was shown previously for GH. Low circulating thyroid hormone levels appear positively correlated with the reduced pulsatile TSH secretion, suggesting that they have, at least in part, a neuroendocrine origin. Finally, the opposite effects of different GH-secretagogues on TSH secretion further delineate particular linkages between the somatotrophic and thyrotrophic axes during critical illness.     

The growth hormone response to hexarelin in patients with Prader-Willi syndrome

Hexarelin (Hex) is a synthetic hexapeptide with potent GH-releasing activity in both animals and men. Aim of this study was to evaluate the GH response to a maximal dose of Hex and GH-releasing hormone (GHRH) in a group of patients with Prader-Willi syndrome (PWS). Seven patients (4 boys and 3 girls, age 2.4-14.2 yr) with PWS, 10 prepubertal obese children (7 boys and 3 girls, age 7.5-12.0 yr), and 24 prepubertal short normal children (11 boys and 13 girls, age 5.9-13 yr) with body weight within +/- 10% of their ideal weight were studied. All subjects were tested on two occasions with GHRH 1-29 at the dose of 1 microgram/Kg i.v., and with Hex at the dose of 2 micrograms/Kg i.v. In the PWS patients the GH response to GHRH (peak = 6.4 +/- 2.0 micrograms/l, p < 0.0001; AUC = 248 +/- 70 micrograms min/l, p < 0.0001) was significantly lower than that observed in the short normal children and similar to that observed in the obese children. In the PWS children the GH response to Hex (peak = 7.5 +/- 1.6 micrograms/l; AUC = 309 +/- 53) was similar to that observed after GHRH and significantly lower than that observed in the obese children (p < 0.05). The results of this study show that PWS patients have a blunted GH response to the administration of a maximal dose of Hex. Whether these findings reflect a more severe pituitary GH deficiency in PWS than in obese children or a deranged hypothalamic regulation of GH secretion need further investigation.     

Evidence for an inhibitory effect of physiological levels of insulin on the growth hormone (GH) response to GH-releasing hormone in healthy subjects

It has been previously reported that in healthy subjects, the acute reduction of free fatty acids (FFA) levels by acipimox enhances the GH response to GHRH. In the present study, the GH response to GHRH was evaluated during acute blockade of lipolysis obtained either by acipimox or by insulin at different infusion rates. Six healthy subjects (four men and two women, 25.8 +/- 1.9 yrs old, mean +/- SE) underwent three GHRH tests (50 micrograms iv, at 1300 h) during: 1) iv 0.9% NaCl infusion (1200-1500 h) after oral acipimox administration (250 mg) at 0700 h and at 1100 h; 2) 0.1 mU.kg-1.min-1 euglycemic insulin clamp (1200-1500 h) after oral acipimox administration (250 mg at 0700 h and at 1100 h); 3) 0.4 mU.kg-1.min-1 euglycemic insulin clamp (1200-1500 h) after oral placebo administration (at 0700 and 1100 h). Serum insulin (immunoreactive insulin) levels were significantly different in the three tests (12 +/- 2, 100 +/- 10, 194 +/- 19 pmol/L, P < 0.06), plasma FFA were low and similar (0.04 +/- 0.003, 0.02 +/- 0.005, 0.02 +/- 0.003, not significant), and the GH response to GHRH was progressively lower (4871 +/- 1286, 2414 +/- 626, 1076 +/- 207 micrograms/L 120 min), although only test 3 was significantly different from test 1 (P < 0.05). Pooling the three tests together, a significant negative regression was observed between mean serum immunoreactive insulin levels and the GH response to GHRH (r = -0.629, P < 0.01). Our results indicate that in healthy subjects, acipimox and hyperinsulinemia produce a similar decrease in FFA levels and that at similar low FFA, the GH response to GHRH is lower during insulin infusion than after acipimox. These data suggest that insulin exerts a negative effect on GH release. Because the insulin levels able to reduce the GH response to GHRH are commonly observed during the day, for instance during the postprandial period, we conclude that the insulin negative effect on GH release may have physiological relevance.     

In obesity, glucose load loses its early inhibitory, but maintains its late stimulatory, effect on somatotrope secretion

Glucose load has a biphasic effect on GH secretion. In fact, in normal subjects, glucose load has a prompt inhibitory and a late stimulatory effect on both spontaneous and GHRH-induced GH levels. The mechanism underlying the inhibitory effect is probably mediated by the increase in hypothalamic somatostatin, whereas that underlying the stimulatory effect is unclear. On the other hand, in obesity, a reduced somatotrope responsiveness to all GH secretagogues is well known, whereas recently, we found that glucose load, but not pirenzepine and somatostatin, fails to inhibit the GHRH-induced GH rise. Thus, the inhibitory effect of hyperglycemia on GH secretion is selectively lacking in obesity. The aim of the present study was to verify whether in obesity the late stimulatory effect of glucose on GH secretion is preserved. We studied 15 female obese patients (OB; age, 33.9 +/- 2.6 yr; body mass index, 36.4 +/- 1.5 kg/m2; waist/hip ratio, 0.9 +/- 0.1) and 12 normal female subjects (NS; 26.5 +/- 1.0 yr; 21.4 +/- 0.3 kg/m2) as controls. Two studies were performed. In study A (six OB and six NS) we evaluated the somatotrope response to GHRH (1 microgram/kg, i.v., at 0 min) alone or preceded by oral glucose (OGTT; 100 g, orally, at -45 min). In study B (nine OB and six NS) we studied the somatotrope response to OGTT (100 g, orally, at 0 min), saline plus GHRH (1 microgram/kg, iv, at 150 min), and OGTT plus GHRH. In study A, the GHRH-induced GH rise in NS was higher (P < 0.01) than that in OB. OGTT blunted the GHRH-induced GH rise in NS (0-90 min area under the curve, 318.9 +/- 39.1 vs. 696.3 +/- 110.8 micrograms/min-L; P < 0.05), but failed to modify it in OB (289.1 +/- 51.7 vs. 283.9 +/- 44.0 micrograms/min-L). In study B, the GHRH-induced GH rise in NS was higher (P < 0.01) than that in OB. OGTT induced a late GH increase in both NS (150-240 min area under the curve, 249.6 +/- 45.2 micrograms/min-L) and OB (103.2 +/- 31.4 micrograms/min-L). Moreover, OGTT enhanced the GHRH-induced GH rise in NS as well as in OB [1433.0 +/- 202.0 vs. 967.9 +/- 116.3 micrograms/min-L (P < 0.03) and 763.8 +/- 131.0 vs. 278.1 +/- 52.3 micrograms/min-L (P < 0.01), respectively]. The GH responses to OGTT alone and combined with GHRH in OB were lower (P < 0.03) than those in NS. Our data show that in human obesity, the oral glucose load loses its precocious inhibitory effect on the GHRH-induced GH rise but maintains its late stimulatory effect on somatotrope secretion. These findings suggest that the inhibitory and stimulatory effects of glucose load on GH secretion are unlikely to be due to biphasic modulation of hypothalamic somatostatin release, which seems selectively refractory to stimulation by hyperglycemia in obesity.     

In vivo responsiveness of morphological variants of growth hormone-producing pituitary adenomas to octreotide

The somatostatin analog, octreotide, is an inhibitor of growth hormone (GH) secretion that has been used to treat patients with GH-producing pituitary tumors. In this study we investigated the in vivo responsiveness to treatment with this analog in patients harboring different morphological types of GH-producing pituitary adenomas. Both GH and insulin-like growth factor I (IGF-I) plasma levels in 30 patients treated with octreotide (300 micrograms/day) for 4 months preoperatively were compared with those from 30 patients who did not receive treatment preoperatively. Tissue samples were studied using ultrastructural and immunohistochemical techniques. Amongst patients harboring densely granulated (DG) adenomas, mean GH levels were reduced to 32 +/- 9% by octreotide, to 30 +/- 7% by surgery and to 26 +/- 9% of baseline by both interventions. Surgery was equally as effective in lowering GH levels in patients with sparsely granulated (SG) adenomas as it was in those with DG adenomas; in patients with SG adenomas, GH levels were reduced by surgery alone to 37 +/- 16% and to 24 +/- 15% when performed following octreotide pretreatment. In contrast, treatment with octreotide alone in patients harbouring SG adenomas reduced GH levels to only 70 +/- 13% of baseline (p < 0.02 compared to surgery alone, or surgery and octreotide). We conclude that the GH inhibitory effects of octreotide are significantly better in patients harboring DG somatotroph adenomas compared with those harboring SG adenomas.     

Favourable effect of olive oil in patients with non-insulin-dependent diabetes. The effect on blood pressure, blood glucose and lipid levels of a high-fat diet rich in monounsaturated fat compared with a carbohydrate-rich diet

The aim of the study was to elucidate the role of the neuropeptide galanin in the regulation of somatotropic and gonadotropic function in normal women. Thirteen normally ovulating (aged 28 to 40 years), non-obese (body mass index, 18.4 to 27.1 kg/m2) women with infertility due to a tubal or male factor were studied. Each woman underwent three tests: (1) bolus intravenous (IV) injection of growth hormone (GH)-releasing hormone (GHRH) (1-29)NH2 1 microgram/kg plus gonadotropin-releasing hormone (GnRH) 100 micrograms at time 0; (2) IV infusion of porcine galanin 500 micrograms in 100 mL saline from -10 minutes; and (3) bolus IV injection of GHRH(1-29)NH2 1 microgram/kg plus GnRH 100 micrograms at time 0 plus IV infusion of porcine galanin 500 micrograms in 100 mL saline from -10 to +30 minutes. All results are expressed as the mean +/- SEM. GH peak after GHRH was 14 +/- 5 micrograms/L; porcine galanin significantly increased serum GH (GH peak, 7.3 +/- 1.2) with respect to baseline levels. No significant differences were observed between either GH peak or GH absolute values after galanin as compared with GHRH alone. Porcine galanin significantly enhanced GH response to GHRH (peak, 31.4 +/- 4.4 micrograms/L) with respect to either GHRH or galanin alone. Luteinizing hormone (LH)/follicle-stimulating hormone (FSH) peaks after GnRH were 16.5 +/- 5.3 and 17.4 +/- 4 IU/L, respectively. Porcine galanin did not cause significant increases in serum LH and FSH levels with respect to baseline.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of pituitary adenylate cyclase-activating polypeptide and vasoactive intestinal polypeptide on cyclic AMP accumulation in sheep pituitary cells in vitro

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) are known to stimulate adenylate cyclase activity in rat pituitary cells but no direct effects have been reported on sheep pituitary cells. In this study we determined whether either peptide could stimulate intracellular cAMP accumulation in dispersed sheep pituitary cells in primary culture. Time course studies with PACAP showed that tachyphylaxis developed rapidly and so a short incubation time (5 min) was used to define the dose-response relationship. PACAP dose-dependently stimulated intracellular cAMP levels with a half-maximum response at 2.9 +/- 0.2 nmol/l (n = 4). In contrast, VIP only caused a small increase in intracellular cAMP levels at the highest dose tested (1 mumol/l). The VIP antagonist [4Cl-D-Phe6,Leu17]VIP had no effect on the cAMP response to either PACAP or VIP while the peptide PACAP(6-38), a putative PACAP antagonist, blocked the cAMP response to PACAP. The desensitisation to PACAP was further investigated by pretreating cells with PACAP for 30 min. After a further 15 min in culture medium alone, these cells showed no cAMP response to subsequent treatment with PACAP but could respond to forskolin. When a longer incubation period of 240 min was used between the first and second treatment with PACAP, a partial return in responsiveness to PACAP was observed. In summary, these results show that PACAP activates adenylate cyclase in sheep pituitary cells but that there is rapid development of tachyphylaxis. Experiments with the antagonists suggest that the response to PACAP is via the PACAP type I receptor. In contrast, physiological doses of VIP do not stimulate cAMP accumulation in sheep pituitary cells.     

Serum concentration of 20K human growth hormone (20K hGH) measured by a specific enzyme-linked immunosorbent assay. Study Group of 20K hGH

Several GH isoforms have been identified in pituitary and serum, the most abundant of which is the 22K human GH (hGH) isoform. The 20K hGH isoform is produced by alternative splicing of GH messenger ribonucleic acid and comprises approximately 10% of all GH in the pituitary. The physiological role of 20K hGH remains to be determined, partly because of the lack of a simple and specific assay. We have established sensitive enzyme-linked immunosorbent assays (ELISAs) specific to 20K and 22K hGH. To determine whether regulation of 20K hGH secretion is the same as that for 22K hGH, we measured serum concentrations of both species of hGH in normal subjects and patients with a variety of endocrine disorders. The serum levels of 20K hGH after overnight fasting was 118 +/- 178 pg/mL (n = 282) in normal women, significantly higher than that in normal men (64 +/- 170 pg/mL; n = 226). However, there was no difference in the proportion of 20K hGH to 20K plus 22K hGH between men (6.3 +/- 2.6%, mean +/- SD; n = 176) and women (6.3 +/- 2.1%; n = 263). No correlation was detected between the ratio of 20K hGH and age, body height, body weight, or body fat mass in normal subjects. The proportion of 20K hGH was significantly (P < 0.001) higher in patients with active acromegaly (9.2 +/- 2.2%; n = 33) and patients with anorexia nervosa (9.0 +/- 1.9; n = 8), both of which are characterized by chronic elevation of circulating GH levels. The proportion of 20K hGH in successfully treated acromegalic patients did not differ from that in normal subjects, suggesting that GH-producing pituitary tumors secrete a higher proportion of 20K hGH, or that a chronic excess of 22K hGH alters the MCR of 20K hGH. The values in patients with adult GH deficiency, hyperthyroidism, primary hypothyroidism, or GH-independent short stature did not differ from those in normal subjects. The 20K ratio did not change after acute GH provocative tests, such as the insulin tolerance test and the GHRH test. These results suggest that secretion of 20K hGH from the pituitary is under the same control as that of 22K hGH. This new assay may provide a tool for understanding the physiological or pathophysiological role of the 20K hGH isoform.