Functioning of the porcine pituitary-adrenocortical axis during neonatal development

A study was conducted with neonatal boars to measure age-related changes in functioning of the pituitary-adrenocortical axis. Pigs were randomly assigned to control (n = 7-10/age) or treated (1-min restraint, n = 9-11/age) groups to be sampled at either 12, 19, or 26 days of age. Blood samples were taken via catheter 10 min before and 3, 10, and 20 min after restraint or at similar time intervals in controls. One day later, pigs were killed and adrenal glands obtained for ACTH receptor measurements. Basal plasma ACTH concentrations were greatest (p = 0.035) on day 12 when compared with later ages, but basal plasma cortisol concentrations were comparable at the three ages. Compared with controls, restraint elevated incremental plasma ACTH and cortisol responses at each age (p < 0.004). On day 12, maximal plasma ACTH (p = 0.0006) and incremental cortisol (p < 0.006) responses to restraint were greater than at later ages. Binding to adrenal ACTH receptors was greatest (p < 0.05) at day 13, which may help explain the apparently increased in vivo response of the adrenal gland to ACTH at this time. Restrained pigs had increased growth rates with increasing age (p = 0.016) whereas growth rates for control pigs did not differ with age. At day 27, 24 h after the 1-min restraint, body weights of restrained pigs exceeded those of control pigs (p = 0.045). At day 20, adrenal DNA and protein in pigs restrained 24 h previously were greater than in control pigs (p < 0.05). These data suggest age-related changes in functioning of the pituitary-adrenal axis in neonatal boars, and an absence of period during neonatal life when the porcine pituitary adrenocortical axis cannot respond to a stressor. The data also indicate both rapid and long-term responses of the adrenal to a very modest stressor and suggest an extreme sensitivity of neonatal pigs to environmental perturbations.     

Brain beta-endorphin and other opioids are involved in restraint stress-induced stimulation of the hypothalamic-pituitary-adrenal axis, the sympathetic nervous system, and the adrenal medulla in the rat

Opiates and opioids have complex effects on the hypothalamic-pituitary-adrenal axis, and they stimulate the sympathetic nervous system. This study was designed to clarify the role of brain beta-endorphin in the mechanism by which stress increases plasma concentrations of adrenocorticotropin (ACTH), epinephrine (E), and norepinephrine (NE). Intracerebroventricular (i.c.v.) administration of beta-endorphin to rats significantly increased plasma ACTH levels at doses of 0.09, 0.3, and 1.5 nmol, and plasma E and NE levels at doses of 0.3 and 1.5 nmol. The rise of plasma ACTH, E, and NE levels by 0.3 nmol beta-endorphin was inhibited by intravenous (i.v.) administration of 2 mg/kg b.wt. naloxone. I.v. administration of anti-rat corticotropin-releasing hormone (CRH) rabbit serum completely blocked the beta-endorphin-induced ACTH secretion without affecting the secretion of E and NE. I.c.v. administration of anti-beta-endorphin rabbit gamma-globulin attenuated a 30-min restraint stress-induced rise of plasma ACTH levels without significant influence on the rise of E and NE levels, whereas i.v. administration of naloxone attenuated the restraint stress-induced rise of plasma ACTH, E and NE levels. These results suggest that i.c.v. administration of beta-endorphin stimulates the secretion of ACTH, E, and NE through opiate receptor, and that brain CRH mediates the beta-endorphin-induced secretion of ACTH. The results also suggest that brain beta-endorphin is, at least in part, involved in the restraint stress-induced stimulation of the hypothalamic-pituitary-adrenal axis, and that some opioids other than beta-endorphin are involved in the stimulatory mechanism of the autonomic nervous system and the adrenal medulla in the rat.     

Non-ACTH POMC fragments stimulate aldosterone production by human adrenal cells in vitro

The possibility that non-ACTH proopiomelanocortin-derived fragments may stimulate aldosterone production has previously been studied using nonhuman cells with inconsistent results. We have examined the response of aldosterone to beta-endorphin (beta-End) and joining peptide (JP) and compared these with the response to ACTH using eight cell suspensions prepared from human adrenal glands. ACTH, 10(-6), 10(-8), and 10(-10) M, consistently stimulated aldosterone accumulation above that occurring in unstimulated cells (150 +/- 83, 120 +/- 62, and 77 +/- 32 fmol/10(4) cells above basal, respectively; mean +/- SE; p < 0.05). beta-End significantly stimulated aldosterone production at 10(-6) and 10(-8) M (114 +/- 84 and 50 +/- 24 fmol/10(4) cells above basal; p < 0.05); 10(-10) M beta-End did not provide significant stimulation. Furthermore, JP stimulated aldosterone biosynthesis (41 +/- 16 fmol/10(4) cells above basal; p < 0.05), only at the highest concentration used, 10(-6) M. The addition of 10(-8) M ACTH plus 10(-6) and 10(-10) M beta-End to human adrenal cells yielded values significantly greater than those achieved with either agent alone (267 +/- 152 and 183 +/- 89 fmol/10(4) cells above basal; p < 0.05). These data indicate for the first time that beta-End and JP have the capacity to stimulate aldosterone production in human adrenal cells in vitro. The physiological and potential clinical significance of these observations has yet to be elucidated.     

Divergent prolactin and pituitary-adrenal activity in rats selectively bred for different dopamine responsiveness

The present study explores the significance of brain dopamine phenotype for individual variation in the neuroendocrine stress response of the rat. For this purpose, we used two Wistar rat lines previously selected for high or low responsiveness of the dopamine system to apomorphine using the gnawing response as the selection criterion. Systemic administration of the drug evoked in apomorphine-susceptible (apo-sus) rats a vigorous gnawing response, whereas apomorphine-unsusceptible (apo-unsus) rats did not gnaw under these conditions. These two rat lines represent individuals displaying extreme differences in gnawing behavior that otherwise coexist in a normal Wistar population. In this study basal and stress-induced hypothalamic-pituitary-adrenal activity and PRL release were measured in chronically cannulated, freely moving rats that endured a conditioned emotional response. Tyrosine hydroxylase messenger RNA (mRNA), corticosteroid receptor mRNA, and in vivo retention of [3H]corticosterone were measured in rat brain sections using in situ hybridization and in vivo autoradiography. The result show that 1) apo-sus rats had a markedly reduced PRL response to stress compared to apo-unsus animals, whereas basal levels were not significantly different. A12 dopaminergic neurons in the arcuate nucleus expressed significantly higher levels of tyrosine hydroxylase mRNA in apo-sus rats, suggesting that the reduced stress-induced PRL release could be due to an increased inhibitory control by dopaminergic neurons; 2) in apo-sus rats, stress resulted in a sustained elevation of ACTH and free corticosterone levels, whereas the total corticosterone levels were not different between the two rat lines; 3) under basal morning conditions, apo-sus rats had significantly higher plasma ACTH, but, in contrast, lower free corticosterone than apo-unsus rats; total plasma corticosterone levels were not different; 4) the basal evening ACTH level was elevated in apo-sus rats; after removal of the adrenals in the morning, this increased ACTH level in apo-sus rats persisted into the afternoon 6 h postadrenalectomy; and 5) hippocampal mineralocorticoid (MR), but not glucocorticoid (GR), receptor capacity for the ligand comparable between the groups; the MR of apo-sus rats displayed an increased retention of [3H]corticosterone in all hippocampal cell fields measured 24 h adrenalectomy; MR and GR mRNA in hippocampus as well as GR mRNA in the paraventricular nucleus were not significantly different in the two rat lines. In conclusion, the data suggest a common genetic background for individual variation in stress responsiveness and dopamine phenotype. High dopamine reactivity is linked to a reduced PRL and an increased ACTH response after stress. These high dopamine responders display a hyporesponsive adrenal cortex and corticosteroid feedback resistance associated with altered brain corticosteroid receptor properties.     

Variation of dorsal horn cell dendritic spread with map scale

OBJECTIVE: To examine the hypothesis that, in polycystic ovary syndrome (PCOS), ovarian steroids induce adrenal enzyme dysfunction or adrenal androgen hyperresponsiveness to ACTH. DESIGN: Prospective controlled clinical study. SETTING: Reproductive endocrinology unit of an academic medical center. PATIENTS: Twelve women with PCOS who had adrenal androgen excess were compared with five weight-matched ovulatory women. In half of the women with PCOS, prestudy screening was suggestive of mild 3 beta-hydroxysteroid dehydrogenase (HSD) deficiency. INTERVENTIONS: Basal and adrenal dynamic blood sampling before and after GnRH agonist (GnRH-a) administration for 6 months. MAIN OUTCOME MEASURES: Basal E2 and androgen levels as well as dexamethasone-suppressed, ACTH-stimulated 17 alpha-hydroxyprogesterone, 17 alpha-hydroxypregnenolone, and androgen levels before and after ovarian suppression. RESULTS: Although none of the subjects with PCOS proved to have mild 3 beta-HSD deficiency, the majority of them (58%) met the criteria for 17,20 lyase hyperactivity before and after GnRH-a therapy. As a group, the remaining subjects with PCOS exhibited an elevated DHEAS response to ACTH before GnRH-a treatment, which may have normalized after GnRH-a treatment. CONCLUSION: Adrenal androgen excess in PCOS may be heterogeneous in etiology, whereas 17,20 lyase hyperactivity appears to be an intrinsic adrenal disorder, adrenal androgen hyperresponsiveness to ACTH may be ovarian induced. Reliance on historical controls may lead to overdiagnosis of mild 3 beta-HSD deficiency.     

Dysregulation of the hypothalamo-pituitary axis in rheumatoid arthritis

OBJECTIVE: To study the dynamic response of the hypothalamo-pituitary- adrenal axis and of prolactin (PRL) pituitary secretion in rheumatoid arthritis (RA). METHODS: We performed a cortisol releasing hormone (CRH) provocation test followed by determination of adrenocorticotropin hormone (ACTH), beta-endorphin, and cortisol concentration, and then a thyrotropin releasing hormone (TRH) provocation test followed by assessment of PRL pituitary secretion in 10 patients with RA and 5 control subjects. All were women under 40 years of age. Hormone concentrations were assessed by radioimmunoassay. RESULTS: Basal PRL cortisol, and ACTH concentrations were similar in patients with RA and controls. We observed a dissociation between the pituitary secretion of beta-endorphin and of ACTH in response to CRH in RA. The ACTH peak and total ACTH production (area under the curve, AUC) were similar in the 2 groups. In contrast, basal beta-endorphin was increased in RA (12.6 +/- 1.41 vs 8.29 +/- 0.144 pg/ml), and the response upregulated (AUC: 83,080 +/- 12,000 vs 54,200 +/- 2400) after CRH compared to controls (p < 0.05). Cortisol adrenal response curve was blunted, but did not reach statistical significance. In contrast, the PRL response to TRH was increased at 120 and 150 min (3461 +/- 303 vs 1897 +/- 520 muIU/ml)(p < 0.01) in patients with RA, independent of disease activity. CONCLUSION: We observed upregulated pituitary PRL secretion in RA, and a dissociation of ACTH stress. The implication concerning the neuroendocrine system in the chronic immune response in RA is discussed.     

Evaluation of itraconazole-dimethyl sulfoxide ointment for treatment of keratomycosis in nine horses

The effect of a 24-h maternal deprivation at day 3 was studied on the hypothalamus-pituitary-adrenal axis of 18-day-old Brown Norway pups, whose stress-hyporesponsive period is similar to other rat strains. Deprivation resulted at day 18 in reduced basal ACTH levels. The rate of onset and the duration of stress-induced ACTH release were enhanced. CRH mRNA, brain corticosteroid mRNA levels and corticosterone receptor levels were not affected by deprivation, but adrenal weight was increased. It is concluded that maternal deprivation has persistently diminished adrenocortical function in containment of the ACTH response to stress.     

Adrenocortical function in patients with active pulmonary tuberculosis

STUDY OBJECTIVE: To assess adrenal function in patients with acute pleuropulmonary tuberculosis (APT) and compare it with that function in patients with community-acquired pneumonia (CAP). PATIENTS: Over a period of 6 months all consecutive patients 18 years of age or older with newly diagnosed APT and CAP were entered into the study. MEASUREMENTS: The whole patients had the following investigations: 1) Serum Na+, K+ and glucose concentrations 2) Systolic and diastolic blood pressures. 3) An ultrasonographic study of the adrenal glands. 4) A standard ACTH stimulation test. RESULTS: There was no significative difference in the serum cortisol level between the two groups at any time of the ACTH stimulation test (basal, 30 and 60 minutes), neither when taking into account the increments between basal and 60 minutes after stimulation serum cortisol levels. All patients in both groups had normal ACTH stimulation test with a peak stimulated cortisol level at 60 minutes > 504 nmol/L. CONCLUSIONS: We did not find evidence of adrenal cortical dysfunction in patients with acute pleuropulmonary tuberculosis or with community-acquired pneumonia in our hospital.     

Release of ouabain-like compound (OLC) from the intact perfused rat adrenal gland

The present study was designed to investigate the effect of ACTH on release of OLC from the intact isolated rat adrenal, perfused in situ. OLC was measured by EIA. The limit of detection of the assay was 23 pmol/10 minutes. Basal levels of OLC varied from 240 to <23 pmol/10 min. Basal corticosterone levels were generally higher than OLC while aldosterone were generally lower. In 3 of the 5 perfusions the addition of ACTH was followed by rapid increases in both OLC and corticosterone secretion rates within 10 minutes of stimulation. Stimulated levels of OLC were 2 to 4-fold and of corticosterone were 3 to 7-fold those found in basal samples. OLC was found to co-elute with authentic ouabain under isocratic HPLC analysis whilst perfusion medium itself contained no detectable OLC immunoreactivity. These preliminary data suggest that the intact perfused rat adrenal preparation is a useful model for investigating the acute regulation of OLC secretion.     

Catecholamine depletion in mice upon reexposure to stress: Mediation of the escape deficits produced by inescapable shock.

Reports 9 experiments with 372 male Swiss-Webster mice in which, immediately following exposure to 60 inescapable shocks, Ss had significantly reduced hypothalamic norepinephrine (NE). Within 24 hrs NE levels returned to control values. Reexposure to as few as 10 shocks 24 hrs after initial stress exposure resulted in significant decline of NE. At this interval after shock, escape performance was severely disrupted, with a large proportion of Ss exhibiting numerous failures to escape shock. Increasing brain dopamine (DA) and NE by levodopa treatment prior to shock prevented the escape deficits. Conversely, pairing 5 inescapable shocks with NE depletion by FLA-63, or both DA and NE depletion by alpha-methylparatyrosine, disrupted escape performance 24 hrs later. Residual drug effects, state dependence, or sustained amine turnover could not account for the behavioral changes. Data are discussed in terms of catecholamine mediation of escape performance through variations in response maintenance abilities. It is suggested that long-term effects of inescapable shock may be due to sensitization effects or conditioned amine depletion. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Laparoscopic vs conventional appendectomy--a meta-analysis of randomised controlled trials

A comparison was made of the dynamics of sympathoadrenal activity in 11 age-matched male and female rats, under basal conditions and after exposure to footshock. Rats were prepared with indwelling catheters in the tail artery 24 h before the experiment. Measurements were made of plasma corticosterone (COR), norepinephrine (NE), epinephrine (EPI), dihydroxyphenylalanine (DOPA), dihydroxyphenylglycol (DHPG) and dihydroxyphenylacetic acid (DOPAC) under resting conditions, after transfer to the shock box (novelty) and at various times after footshock. Under basal conditions, males have significantly higher blood pressure and plasma DHPG/NE ratios but lower plasma levels of COR, NE and DOPAC than females. Three min after exposure to the shock chamber (novelty stress) there were significant increases in COR, EPI, NE and DHPG in both sexes, while DOPA increased only in females and DOPAC remained unchanged in both sexes. Footshock produced a further increase in EPI, NE and DOPAC within 2 min, which lasted about 15 min. There were significant sex differences in the extent and duration of the response of COR, EPI and DHPG. The data show that the female sympathoadrenal system is more reactive than that of the male to the stresses of a novel environment and footshock. The smaller DHPG/NE ratios in females at rest and after stress suggest that neuronal uptake of NE is lower in females than in males. The finding that stress produces larger increments of plasma DOPA and DOPAC in female rats indicates that tyrosine hydroxylase in the sympathetic nerve terminals and adrenal medulla may also be higher than in males.     

Acute changes in norepinephrine content in the median eminence induced by orchidectomy or testosterone replacement

Median eminence catecholamines were measured in individual samples from intact, castrated, or sham-operated male rats, in order to correlate changes in catecholamine content with the early post-castration rise in serum LH levels. Both norepinephrine (NE) and dopamine (DA) were measured by an enzymatic-isotopic assay and advantage was also taken of a method recently developed that makes it possible to obtain the median eminence free of the surrounding hypothalamus. Determinations were made at 4, 8, or 24 h after surgery. All animals were killed between 1400 and 1600 h. It was observed that castration increases the ME content of NE significantly at all the times studied, with peak values 8 h after orchidectomy. Sham operation induced a significant decrease in NE content in the ME 4 h after surgery. By 8 h the NE values had returned to intact control levels. Both castration and sham operation induced a significant decrease in DA levels 4 h after surgery. By 8 h, DA values had returned to intact control levels in both groups. When the NE levels in castrated rats had reached the highest value, serum LH values had not departed from control levels, indicating that the change in NE content in the ME takes place prior to the expected rise in LH. Testosterone replacement therapy (40 mug/100 gBW) of castrated rats blocked the increase in NE content observed 8 h after castration. Dopamine levels were not affected by this treatment. These results support the concept that the NE contained in median eminence catecholaminergic terminals participates in the feed-back regulation of LH secretion in the male rat, while DA is apparently not involved under the present conditions.     

Hypofunction of the stress axis in Sj?gren's syndrome

OBJECTIVE: To examine the functional integrity of the hypothalamic-pituitary-adrenal (HPA) and thyroid axes in Sj?gren's syndrome (SS) via the assessment of basal and stimulated adrenocorticotropin (ACTH), cortisol, thyroid stimulating hormone (TSH), and prolactin levels. METHODS: Pituitary function of the HPA axis was assessed by determining the basal plasma levels of ACTH in the late afternoon, as well as the ACTH released to ovine corticotropin releasing hormone (oCRH) stimulation; adrenal function was assessed by measuring plasma cortisol levels in the late afternoon at baseline and after release of the endogenous ACTH during oCRH stimulation. Basal and thyrotropin releasing hormone (TRH) stimulated levels of TSH and prolactin were also assessed. Healthy volunteers were used as controls. RESULTS: Patients with SS, compared to controls, were characterized by significantly lower ACTH levels (pg/ml), (5.1 +/- 0.5 vs 11.4 +/- 1.5, respectively; p < 0.05) and cortisol levels (microg/ml), (2.4 +/- 0.6 vs 5.9 +/- 1.2, respectively; p < 0.05). Furthermore, a blunted pituitary and adrenal response to oCRH compared to controls was observed: peak plasma ACTH and cortisol levels for patients with SS were 46.2 +/- 5.4 pg/ml and 15.7 +/- 1.6 microg/ml, respectively, and for controls 61.5 +/- 3.8 and 19.6 +/- 0.7, respectively (p < 0.05). Basal TSH levels were significantly elevated in patients (1.3 +/- 0.3 microIU/ml vs 0.9 +/- 0.05 microIU/ml; p < 0.05). CONCLUSION: The above findings indicate hypoactivity of the HPA axis in patients with SS. Further studies are needed to definitively identify the locus of the defects and assess the significance of the pattern of the perturbations to the pathogenesis and expression of SS.     

Four-week ethanol intake decreases food intake and body weight but does not affect plasma leptin, corticosterone, and insulin levels in pubertal rats

Long-term intake of ethanol decreases food intake and inhibits growth in experimental rats. The aim of this study was to determine the effect of 4-week oral ethanol ingestion on plasma leptin and adrenal function. Male 45-day-old Wistar rats were divided into three groups: absolute control (AC), ethanol (E) administered 10% (wt/vol) ethanol instead of tap water, and pair-fed (PF) given an amount of food corresponding to the food intake of E animals. E rats consumed less pelleted diet (74% cumulative total intake); however, this caloric deficit was compensated by ethanol ingestion. Net water intake in E animals was 76% of that in the control groups. The body growth of both E and PF rats was stunted compared with AC animals, but E rats were heavier than PF rats. The plasma leptin level was similar in E and AC and decreased in PF animals. There were no differences in plasma osmolality or glycemia among the three groups. Plasma insulin was decreased in PF compared with both AC and E rats. Plasma corticosterone was not affected by ethanol, but was increased in the food-restricted (PF) group. Although there were no differences in basal adrenal corticosterone production in vitro, there was a slightly higher response to corticotropin (ACTH) in E rats. We conclude that drinking 10% ethanol decreased the dietary intake and body growth. These changes were not mediated by plasma leptin changes. Although alcohol ingestion and its energy content theoretically normalized the total energy intake and prevented the decrease of plasma leptin, the growth of young rats was inhibited. Drinking 10% ethanol instead of tap water for 4 weeks did not stimulate basal adrenal activity.     

Adrenocortical responsiveness to adrenocorticotropic hormone is enhanced in chronically food-restricted rats

Chronic food restriction (FR) of rats and mice results in moderate hyperadrenocorticism, which may play a role in activating cellular mechanisms that retard aging. Previously, we reported that the FR-induced hyperadrenocorticism is not due to an activated hypothalamo-pituitary unit. Therefore, we investigated in a series of experiments whether adrenal responsiveness to adrenocorticotropic hormone (ACTH), in vitro and in vivo, is enhanced by FR. Three mo-old male Fischer 344 rats were either given free access to food (AL rats) or restricted to 60% of food consumed by AL rats (FR rats) from 6 wk of age. They were killed by decapitation in the morning (AM) and afternoon (PM) when endogenously circulating corticosterone levels are at their nadir and peak, respectively. In vitro, adrenal glands from FR rats (1.5 mo FR) produced more corticosterone per mg at all doses of ACTH than those from AL rats in both the AM and PM (diet main effect, P < 0.001). FR (1.5 to 2.5 mo) also enhanced adrenal responsiveness to physiologic (diet main effect, P < 0.05) and superphysiologic (diet main effect, P < 0.001) levels of ACTH administered in vivo to dexamethasone-treated rats. ACTH-receptor (ACTH-R) mRNA, normalized to adrenal mass or to total RNA, was not influenced by FR (1.5 mo). However, adrenal ACTH-R mRNA, as well as adrenal mass, per unit body weight was greater in FR than in AL rats (diet main effect, P < 0.001). These results indicate that enhanced adrenocortical responsiveness to ACTH plays a major role in the hyperadrenocortical state of chronically FR rats.     

Evidence for two differentially regulated populations of peripheral beta-endorphin-releasing cells in humans

In the current study we tested the hypothesis that human plasma beta-endorphin (beta E) is derived from at least two subpopulations of beta E-releasing cells: one sensitive to glucocorticoids as well as to dopamine (DA; regulated analogously to the corticotrophs of the rat pituitary), and one insensitive to glucocorticoids but sensitive to DA (regulated analogously to the melanotrophs of the rat pituitary). To test this hypothesis, human plasma levels of ACTH, cortisol, and beta E-like immunoreactivity were measured at baseline and after haloperidol treatment (0.05 mg/kg, i.v.) in two experimental groups, one pretreated with dexamethasone (1.5 mg) and one pretreated with placebo. Plasma PRL levels were also measured in both groups as an indicator of DA receptor blockade. Dexamethasone partially suppressed both baseline and haloperidol-stimulated levels of human plasma beta E-like immunoreactivity, whereas it completely suppressed both basal and haloperidol-stimulated levels of ACTH and cortisol and had no statistically significant effect on either basal or haloperidol-stimulated PRL levels. These data support a negative feedback effect of glucocorticoids on one DA-sensitive cell population that releases both ACTH and beta E (corticotroph like), but not on a second cell population that releases beta E but not ACTH.     

Reconstructive spine surgery in pediatric patients with major loss in vital capacity

The effects of exogenenous monoaminergic neurotransmitters (norepinephrine, NE; epinephrine, E; dopamine, DA and 5-HT) and inhibin alpha N-terminal fragments P32 (1-32), P32-Tyr on P4 production by incubated rat CL cells were studied. The results demonstrated that: (1) alpha fragments caused significant inhibition on P4 production. (2) 0.1 mmol/L NE (or E) and 10 mumol/L DA produced a marked increase in both basal and hCG induced P4 production by CL cells (P < 0.001). The rank orders of potency of the catecholamines in stimulating P4 production were different, for basal P4 production, NE > E > DA; but for hCG induced P4 production, DA > E > NE, i.e. the order just reversed. Addition of P32-Tyr significantly neutrolized the stimulatory action of E, but only slightly increased the action of NE. (3) alpha receptor blocker phentolamine and beta receptor blocker propranolol were effective in decreasing basal and hCG-induced P4 production, the latter being more effective than the former. It was further shown that both blockers augmented the inhibitory effect of alpha-fragments on P4 production. (4) Unlike NE, E, and DA, 5-HT at 0.5 mumol/L exerted inhibitory effect on the basal and hCG-induced P4 production, but profoundly supressed the inhibitory effect of alpha-fragments on P4 production. The above results suggested: (1) Adrenergic, DA and 5-HT receptors are present in rat CL, where catecholamine might exert a stimulating effect on basal and hCG-induced P4 production via different pathways. (2) The inhibitory effect of P32, P32-Tyr on P4 production might be related to their inhibition by partial blocking alpha/beta receptors, which were antagnized by 5-HT. (3) The action of P32, P32-TYr on P4 production is brought on the participation of neurotransmitters NE, E, DA and 5-HT.     

Antibody to keyhole limpet hemocyanin labels retinal horizontal cells in some amphibians, but not in others

The intact rat adrenal gland in short-term (3-h) organ culture may be amenable for the identification of factors involved in regulating adrenal cell apoptosis under defined conditions. In this model, culturing in the absence of trophic support (basal; control) triggered apoptosis in the intact rat adrenal gland; oligonucleosome formation, a measure of apoptosis, was 56.4-fold greater than that of glands snap-frozen at the start of incubation. Angiotensin II (Ang II) (100 nM) enhanced apoptosis by 67% over control. By contrast, adrenocorticotropin (ACTH) (100 nM) attenuated basal apoptosis by 59% and antagonized the enhanced apoptosis induced by Ang II back to the control level. Quartering of the glands enhanced basal oligonucleosome formation 182.2% greater than that of intact glands. Interestingly, quartering of the glands abolished the influences of Ang II and ACTH on apoptotic DNA fragmentation, but did not alter ACTH-induced corticosterone secretion. These data suggest that some level of gross adrenal structural information or compartmentalization, sufficiently disrupted by quartering, is required for the hormonal modulation of adrenal cell survival.     

Extracellular striatal concentrations of endogenous 3,4-dihydroxyphenylalanine in the absence of a decarboxylase inhibitor: a dynamic index of dopamine synthesis in vivo

Basal levels of endogenous 3,4-dihydroxyphenylalanine (DOPA) were detected by HPLC coupled with coulometric detection in dialysates from freely moving rats implanted 48-72 h earlier with transversal dialysis fibers in the dorsal caudate. Because decarboxylase inhibitor is absent in the Ringer's solution, this method allows monitoring of basal output of dopamine (DA) and 3,4-dihydroxyphenylacetic acid, as well as DOPA. Extracellular DOPA concentrations were reduced by the tyrosine hydroxylase inhibitor alpha-methylparatyrosine (200 mg/kg, i.p.) and by the dopaminergic agonist apomorphine (0.25 mg/kg, s.c.). The dopaminergic antagonist haloperidol (0.2 mg/kg, s.c.) stimulated DOPA output by about 60% over basal values. Gamma-Butyrolactone, at doses of 700 mg/kg, i.p., which are known to block dopaminergic neuronal firing and which reduce DA release, stimulated DOPA output maximally by 130% over basal values. Tetrodotoxin, which blocks DA release by blocking voltage-dependent Na+ channels, increased DOPA output maximally by 100% over basal values. The results indicate that basal DOPA can be detected and monitored in the extracellular fluid of the caudate of freely moving rats by transcerebral dialysis and can be taken as a dynamic index of DA synthesis in pharmacological conditions.     

Augmented ACTH responses to stress in adrenalectomized rats replaced with constant, physiological levels of corticosterone are partially normalized by acute increases in corticosterone

Adrenalectomized rats replaced with constant, physiological levels of corticosterone via a subcutaneous pellet (Pellet) have normal basal morning ACTH but exhibit enhanced and prolonged ACTH responses to stress vs. sham-operated (Sham) rats. It has not been determined if the lack of either stress-induced or circadian increases in corticosterone, both of which are missing in Pellet rats, may account for this enhanced response. To test the extent to which stress-associated increases in corticosterone alone can normalize stress-induced hypersecretion of ACTH, we approximated endogenous secretion by injecting additional corticosterone in Pellet rats via an indwelling subcutaneous cannula, 5 min before hypoxia stress (10% O2). A corticosterone dose of 666 micrograms/kg (Pellet+B), but not 333 micrograms/kg (Pellet+Low B), produced plasma corticosterone levels comparable to those in Shams and normalized stress-induced but not post-stress plasma ACTH. Administration of the type II corticosteroid receptor antagonist RU 38486 30 min before corticosterone reversed this inhibition. We conclude that enhanced ACTH responses to stress in Pellet rats result in large part from lack of type II receptor-mediated feedback inhibition by corticosterone increases during stress, although prior circadian increases in corticosterone may also be required.