ACTH response to a low dose but not a high dose of bacterial endotoxin in rats is completely mediated by corticotropin-releasing hormone

In experimental animals and humans, bacterial endotoxin activates the hypothalamus-pituitary-adrenal (HPA) axis. The pathways by which endotoxin stimulates adrenocorticotropic hormone (ACTH) and corticosterone secretion are uncertain. In the present study we compared the role of hypothalamic corticotropin-releasing hormone (CRH) in the activation of the HPA axis by a low (2.5 micrograms/kg) and a high (2.5 mg/kg) dose of bacterial endotoxin. Two experimental models were applied using chronically cannulated male Wistar rats. In the first model, rats were subjected to lesions of the hypothalamus that interrupted dorsal, lateral and frontal input to the median eminence (anterolateral deafferentation) or to sham operation and rats were used 7 days later. Before and at hourly intervals after endotoxin (2.5 micrograms/kg i.p.), blood samples were taken for the determination of plasma ACTH and corticosterone concentrations. Deafferentation of the hypothalamus strongly attenuated the elevations in plasma ACTH and corticosterone concentrations by a low dose of endotoxin compared to the responses in sham-operated animals. The second model involved passive immunization to CRH using a monoclonal antibody to rat/human CRH (PFU83). PFU83 (90 nmol/rat) abolished the elevation of plasma ACTH concentrations and attenuated corticosterone responses to a low dose of endotoxin (2.5 micrograms/kg i.p.) compared to that in control IgG-treated rats. Since the corticosterone responses to endotoxin were less effectively inhibited by the antibody than the ACTH responses, we postulate that non-ACTH-dependent mechanisms may contribute to the corticosterone response to endotoxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypothalamic paraventricular nucleus lesions differentially affect serotonin-1A (5-HT1A) and 5-HT2 receptor agonist-induced oxytocin, prolactin, and corticosterone responses

A number of receptor subtypes mediate hormonal responses to serotonin (5-HT). To test the hypothesis that the hypothalamic paraventricular nucleus (PVN) mediates 5-HT1A and 5-HT2 receptor-mediated oxytocin, PRL, and corticosterone responses, we studied the effects of the 5-HT1A agonist ipsapirone and the 5-HT2A/2C agonist 1-(2,5-dimethoxy-4-iodophenyl)2-aminopropane (DOI) after surgical PVN lesions or sham operations. Chronically cannulated, conscious, freely moving, male Wistar rats were injected iv (1 mg/kg) shortly after (3-4 days) and 5 weeks after (35-37 days) the operations. In sham-operated rats, ipsapirone caused marked elevations in plasma PRL and corticosterone, but not oxytocin concentrations, whereas DOI increased plasma concentrations of all three hormones. Short term PVN lesions prevented ipsapirone-induced corticosterone and DOI-induced oxytocin responses. DOI-induced PRL and corticosterone responses were also markedly inhibited 3-4 days after lesioning, although small rises over the baseline values were still observed. The ipsapirone-induced PRL response was unaffected by the lesioning. Five weeks after PVN lesioning, partial recoveries were observed in ipsapirone- and DOI-induced corticosterone and DOI-induced oxytocin responses, whereas DOI-induced PRL responses remained suppressed. The present findings suggest that the PVN or neural pathways close to it mediate oxytocin, PRL, and corticosterone responses to the 5-HT2 receptor agonist DOI as well as corticosterone, but not PRL, responses to the 5-HT1A receptor agonist ipsapirone. The results after long term PVN lesioning show that the oxytocin and corticosterone responses may be partially restored with time after lesioning.

Corticotroph, somatotroph and mammotroph cell kinetics in the postnatal infant female rat

The aim of this work was to detect if hypothalamic-pituitary maturation was accompanied by significant proliferation changes in differentiated pituitary cell pools. For this purpose, pituitary corticotroph (Ct), mammotroph (Mt) and somatotroph (St) proliferation activities were scanned in intact female rats during the postnatal (P) period (1-35 postnatal days). The techniques of tritiated thymidine labelling, immunostaining and autoradiography were combined to visualize DNA synthesis of hormone containing cells. Immunoreactive cell densities were measured using image analysis, and double labelled cells were counted. Corticotroph proliferation activity increased significantly on day P12, followed by an increase in the Ct proportion on days P13-14. This is the first observation of a spontaneous change of corticotroph proliferation at the end of the stress nonresponsive period. The mammotroph density and proliferation rate increased gradually during postnatal maturation, until the Mt pool overran other cell types of the female hypophysis on day 35. The somatotroph pool was the most numerous until day P20; the proliferation rate remained constant while St proportions increased reaching a plateau between days P13 and 20, then decreased to the adult level. Each cell type examined showed a characteristic, individual density and proliferation pattern.

New Gaba-containing analogues of human growth hormone-releasing hormone (1-30)-amide: I. Synthesis and in vitro biological activity

Analogues of human growth hormone-releasing hormone (1-30)-amide have been developed. All analogues have been modified in position 27 with Nle and with Gaba in position 30. Additional D-amino-acids have been inserted in the GHRH(1-30)-NH2 sequence: A-1741: Nle27,Gaba30-GH-RH(1-30)-NH2 A-495: D-Ala2,Nle27,Gaba30-GH-RH(1-30)-NH2 A-515: D Ala2,Leu15,Nle27,Gaba30-GH-RH(1-30)-NH2 A-527: D-Ala2,D-Arg11,Leu15,Nle27,Gaba30-GH-RH(1-30)-NH2. Our analogues were synthesized by solid phase peptide synthesis and were tested is two different in vitro systems and in rat pituitary cell cultures. A-495 and A-1741 were found to be the most active in releasing GH, however they showed different activities in the two different test systems. A-495 exhibited higher potency in the superfusion system (1.63 fold potency of the GHRH (1-29)-amide), while A-1741 evoked higher GH release from cultured pituitary cells (1.5-2.5 times higher than the GH-RH(1-44)-amide). The other analogues (A-515 and A-527) were found to be equipotent to the standard molecule. We can conclude that Nle27 and Gaba30 substitutions appeared to be a good modification in in vitro test systems, and Gaba30 substitution served as a good spacer during the synthesis, since it made the coupling of the C-terminal amino acids easier and produced quantitative coupling. In addition to the advantageous properties in the synthesis these modifications with or without D-Ala at the N-terminus increased the in vitro biological activity to 1.5-2.5 fold of the GHRH molecule.(ABSTRACT TRUNCATED AT 250 WORDS)

Denervation of the rat posterior pituitary gland: validation of a stereotaxic method

A stereotaxic surgical method was developed for interrupting the nerve fibres running through the rat pituitary stalk to the posterior pituitary gland without obliterating the hypothalamo-pituitary portal circulation. The pituitary stalk was compressed by the blunt tip of an L-shaped rotating knife. Successful operations produced mild diabetes insipidus, disappearance of arginine vasopressin from the neural lobe, accumulation of arginine vasopressin and neurosecretory material in the pituitary stalk and no infarction in the anterior lobe of the pituitary gland. In female rats, the oestrous cycle was only temporarily disturbed. Plasma prolactin and corticosterone levels were high during the first 24 h after the stalk compression but returned to normal baseline levels from the second day after the operation. One week after the operation plasma adrenocorticotropin and prolactin levels were in the control range while plasma alpha-melanocyte-stimulating hormone was elevated. Denervation of the posterior pituitary gland may help in studying the neural control of intermediate lobe function and the role of the neural lobe in various endocrine conditions, and may serve as a model for lesions of the pituitary stalk and formation of ectopic neurohypophysis in the human.

gamma-Aminobutyric acid-induced elevation of intracellular calcium concentration in pituitary cells of neonatal rats

Gamma-aminobutyric acid (GABA) increased intracellular calcium concentration ([Ca2+]i) of newborn rat pituitary cells in suspension measured by the FURA-2 method. The effect of GABA was dose dependent in the range of 0.1-10 microM. This effect diminished with postnatal age as measured at days 2, 14 and 21, and in adult animals. The GABA stimulation was mimicked by muscimol; in contrast, baclofen (up to 100 microM) was ineffective. Picrotoxin, a GABAA antagonist interacting with GABA-activated chloride ionophores, caused a dose-dependent inhibition of the [Ca2+]i elevating effect of 100 microM GABA or muscimol. These observations indicate the involvement of GABAA type receptors. The GABA or muscimol effect on [Ca2+]i was antagonized by nifedipine (10 microM) or verapamil (50 microM), and completely abolished in the presence of 4 mM EGTA (low-calcium medium). The findings indicate the presence of depolarizing GABAA receptors on neonatal rat pituitary cells. It seems very likely that the mechanism by which GABA receptor occupation results in elevated [Ca2+]i is a membrane depolarization by increased Cl- conductance followed by calcium influx through L-type voltage-dependent calcium channels.

Paraventricular and supraoptic nuclei of the hypothalamus are not equally important for oxytocin release during stress

The relative importance of the paraventricular (PVN) and the supraoptic nuclei (SON) for the secretion of oxytocin was evaluated by comparison of stress-induced oxytocin release under normal conditions, in the absence of vasopressin and/or corticoliberin (CRF). We introduced an incomplete anterolateral cut (iALC) around the mediobasal hypothalamus designed to leave intact the SON-neurohypophysial connections but to inflict damage to the nerve fibers from the PVN. The studies were performed in conscious cannulated rats using immobilization as the stress stimulus. Stress-induced oxytocin release was found in heterozygous Brattleboro rats as well as in homozygous animals lacking vasopressin, yet in the latter it was less pronounced and in both cases it was prevented by iALC. In Wistar rats, stress-induced oxytocin release was markedly reduced after iALC and absent after PVN lesion. Both hypothalamic interventions failed to influence basal oxytocin levels and resulted in a similar reduction of ACTH release. It is concluded that a functional diversity exists between the hypothalamic magnocellular nuclei. At least in relation to immobilization stress, the PVN is essential for stress-induced oxytocin release and it is evident that the SON without the PVN cannot preserve oxytocin secretion during stress.

Factors from the paraventricular nucleus mediate inhibitory effect of alpha-2-adrenergic drugs on ACTH secretion

The controversy about putative stimulatory and inhibitory functions of catecholamines in regulation of ACTH secretion has been recently shifted towards a consensus that during stress catecholamines stimulate corticotropin-releasing factor (CRF-41) containing neurons through alpha 1-adrenoreceptors, while inhibiting their own secretion acting on presynaptic alpha 2-receptors. In this study the effect of the alpha 2-agonist clonidine and the antagonist CH-38083 was studied on exogenous CRF-41/AVP-induced ACTH secretion in rats with/without paraventricular nucleus lesion. Clonidine (30 micrograms/kg) attenuated CRF-41/AVP (1 pmol/10 pmol)-induced ACTH secretion in sham-operated rats, but was ineffective in reducing CRF-41/AVP-induced ACTH secretion in rats with paraventricular nucleus lesion. In sham-operated rats, alpha 2-receptor antagonist CH-38083 slightly elevated the basal, and significantly potentiated the CRF-41/AVP-induced ACTH secretion, while it had no effect on the hypophyseotropic cocktail-induced ACTH response in paraventricular-lesioned rats. Neither the agonist nor the antagonist affected CRF-41/AVP-induced ACTH release from pituitary fragments in vitro. These results suggest that in response to activation of alpha 2-adrenoreceptors a corticotropin release-inhibiting substance is released from the paraventricular nucleus.

Significance of chloride channel activation in the gamma-aminobutyric acid induced growth hormone secretion in the neonatal rat pituitary

Growth hormone (GH) secretion of the neonatal pituitary is stimulated by tau-aminobutyric acid (GABA) (1,2). Since in most cases GABA is known to act by increasing postsynaptic membrane permeability to chloride ions we tested the importance of chloride channel activation in the GH stimulatory effect of GABA in the neonatal pituitary. In the absence of chloride in the superfusion medium GABA was without effect on GH secretion of the neonatal pituitaries and its effect was attenuated by chloride channel inhibitors. The effect of growth hormone releasing hormone (GHRH) on GH secretion was attenuated in the chloride-free media, but it was not affected by simultaneous administration of chloride channel blockers. The present study indicates that GH stimulatory effect of GABA in the neonatal pituitaries might involve chloride channel activation probably resulting in secondary activation of calcium channels.

Influence of oligopeptide aldehydes on intracellular Ca2+ concentration in rat pituitary cells

We investigated the effects of some synthetic tripeptide aldehydes, earlier shown to influence pituitary hormone secretion and 45Ca2+ uptake, on the intracellular free Ca2+ concentration ([Ca2+]i) of rat anterior pituitary cells in suspension. Boc-D-Phe-Leu-Phenylalaninal or Boc-D-Phe-Leu-Prolinal in the tested range of 1-100 or 200 microM, respectively, were ineffective in influencing basal [Ca2+]i but caused a concentration-dependent inhibition in K+ (25 mM)-induced [Ca2+]i elevation. The IC50 of both effects was about 50 microM. In contrast, they did not interfere with the stimulation caused by the calcium channel agonist BAY K 8644 and were also ineffective in influencing the receptor-mediated stimulus of thyrotropin-releasing hormone on [Ca2+]i. On the basis of the present and foregoing results the possible involvement of calcium channels is discussed, but different mechanisms mediating the tripeptide aldehyde inhibition are also considered. A third tripeptide aldehyde, Boc-Gln-Leu-Lysinal (Boc-GLL), showed ionophore-like properties. This nontoxic substance caused a dose-dependent rise up to 400% (at 100 microM) in [Ca2+]i. Its effect is not mediated by voltage-dependent calcium channels, as it cannot be inhibited either by the classical calcium channel antagonists verapamil and nifedipine, or by the above-mentioned inhibitory tripeptide aldehydes. When we decreased the extracellular Ca2+ concentration by the addition of 4 mM EGTA, the effect was inverted and Boc-GLL caused a large fall in [Ca2+]i. We suggest that Boc-GLL may open cell membrane pores through which Ca2+ moves along the concentration gradient.(ABSTRACT TRUNCATED AT 250 WORDS)

Possible mediation of GABA induced growth hormone secretion by increased calcium-flux in neonatal pituitaries

Gamma-aminobutyric acid (GABA) stimulates growth hormone (GH) secretion from pituitaries of young (less than 20-day old) rats (1,2). Present work revealed that the GH stimulatory effect of GABA was abolished in the absence of calcium and response was attenuated by Nifedipine. The calcium efflux from 45CaCl2 preloaded neonatal pituitaries was enhanced by GABA or by muscimol, and this effect was antagonized by the GABA antagonist picrotoxin. In pituitaries of 21 day old or adult rats GABA stimulated neither GH secretion nor calcium efflux. These results indicate that in neonatal pituitaries GABA influences calcium transport and its GH releasing effect is linked to the presence of calcium.

Prolactin response to morphine in intact and adrenalectomized lactating rats

To examine the hypothesis that the increased adrenocortical activity during lactation induced the loss of the prolactin (PRL) -releasing effect of morphine, we studied the effect of morphine in adrenalectomized (ADX) and sham-operated primiparous lactating Wistar rats. Animals were adrenalectomized 4 days after delivery. On day 11 of lactation (7 days after ADX), pups were separated from their mother 2 h before morphine or haloperidol injection. Intravenous injection of 5 mg/kg morphine did not change plasma PRL levels in the sham-operated lactating rats, but it resulted in a significant increase of plasma PRL levels in ADX lactating animals, with or without corticosterone replacement. Catalepsy following 10 mg/kg i.v. morphine was also markedly enhanced in ADX lactating animals. The PRL response to 0.5 mg/kg haloperidol was higher in ADX lactating animals than that in the controls. Morphine given 2 h after haloperidol treatment resulted in a further increase of plasma PRL in ADX, but not in the sham-operated lactating animals. These results suggest that adrenal hyperfunction may lead to a loss of sensitivity to morphine during lactation.

Effect of dexamethasone implanted in different brain areas on the morphine-induced PRL, GH and ACTH/corticosterone secretion

We studied the effect of dexamethasone (DEX) implantation in male Wistar rats to elucidate the site of action of morphine-induced prolactin (PRL), growth hormone (GH), adrenocorticotropic hormone (ACTH) and corticosterone (B) secretion. DEX or cholesterol was implanted in the close vicinity of the paraventricular (PVN), or the arcuate nuclei (ARN) of the hypothalamus or into the hippocampus. Five days after implantation blood samples were taken 30 min after i.p. morphine by decapitation or through an indwelling cannula 15, 30, 60 min after i.v. injection. DEX implanted near the PVN resulted in a blockade of morphine-induced ACTH and B secretion. In contrast, GH response to morphine was enhanced, while that of PRL was unchanged. DEX implanted near the ARN significantly inhibited the PRL-releasing effect of morphine, but was without any influence on the PRL secretion induced by haloperidol. There was a partial reduction in the B response to morphine, and GH secretion was unchanged. Dorsal hippocampal implants were without any effect on the morphine-induced GH, PRL or B secretion. We suggest that the site of glucocorticoid inhibitory action in the hypothalamus is the PVN for the opiate-induced ACTH/B secretion, and the ARN for the morphine-induced PRL release. The enhanced GH response to morphine observed in DEX-PVN implanted rats might be due to a decreased somatostatin tone.

Do the circulating neurohypophysial hormones affect basal or stress induced prolactin (PRL) release in male rats?

The action of acute administration of oxytocin (OXY), vasopressin (AVP) or its analog 1-deamino-8-D-arginine-vasopressin (dDAVP) on basal and stress induced PRL release in normal male rats and the effect of chronic injection of AVP on PRL stress response in AVP deficient rats were studied. The hormones (OXY, 600 ng min-1 per rat; AVP 6, 12 or 24 ng min-1 per rat and dDAVP 24 ng min-1 per rat) were infused to conscious rats via the jugular vein for 10 min and then the rats were immobilized under continuing the infusion for further 20 min. In parallel experiments arterial blood pressure (BP) was measured. OXY and 24 ng min-1 AVP caused high BP elevation of the same magnitude, yet the effect of 12 ng min-1 AVP was significantly lower. Neither OXY, dDAVP, nor 6 and 12 ng min-1 of AVP affected basal or stress stimulated PRL values when compared with saline treated animals. 24 ng min-1 of AVP highly stimulated nonstressed PRL levels and no additional stress effect was observed. Intramuscular injection of 2 micrograms (1 U) of AVP daily for 7 days did not influence the basal values or stress induced PRL response in Brattleboro homogygous rats as compared with vehicle treated controls or heterozygous rats treated with AVP or vehicle. These results show that the infusion of 24 ng min-1 per rat of AVP stimulated PRL release which cannot be explained by the nonspecific effect of high BP. Repeated AVP administration did not modulate either the basal or IMO stress stimulated PRL secretion in rats with or without genetic vasopressin deficiency.

Anterolateral hypothalamic deafferentation inhibits histamine-induced prolactin secretion and potentiates TRH-induced thyrotropin secretion in male rats

We studied the effect of histamine on serum prolactin and thyrotropin (TSH) levels in male rats with anterolateral hypothalamic deafferentation of hypothalamic connections or anterolateral cut (ALC). The success of ALC was confirmed by immunohistochemistry of somatostatin (SRIF) in the medial basal hypothalamus. ALC did not affect basal prolactin or TSH levels. Thyrotropin-releasing hormone (TRH, 200 ng/rat, i.p.) did not affect prolactin secretion either in sham-operated or ALC rats. In sham-operated rats intracerebroventricularly administered histamine increased significantly prolactin levels. Hypothalamic deafferentation abolished the effect of histamine on prolactin levels. TRH increased significantly serum TSH levels both in sham-operated controls and ALC rats. In the latter, however, the TSH-secretory response to TRH was significantly (p less than 0.05) larger compared to the controls. Intracerebroventricularly infused histamine (2 micrograms/rat) did not change the TRH-induced TSH secretion in either group of rats. These results show that (1) the effect of histamine on prolactin secretion is mediated through nerve tracts which are destroyed by ALC, and (2) cutting of afferent TRH (through sensitization) and SRIF fibers (through lacking inhibition) entering medial basal hypothalamus may both contribute to the enhanced TSH response to exogenous TRH.

Inhibition of suckling-induced prolactin release by dexamethasone

The effect of dexamethasone (DEX) treatment (400 and 200 micrograms/kg BW 21 and 2 h before suckling stimulus, respectively) on suckling- and domperidone (DOMP)-induced PRL release was investigated in freely moving, primiparous lactating rats. DEX completely blocked suckling-induced plasma PRL release without affecting DOMP-induced release of the hormone suggesting a central action of DEX. The effect was transient because it could not be detected on the second day of testing. The effect of DEX implanted in three different brain areas on suckling- and DOMP-induced PRL release was also tested. Implants surrounding the hypothalamic paraventricular nuclei and dorsal hippocampus failed to affect PRL release induced by suckling stimulus. Surprisingly, DEX suppressed PRL release induced by suckling stimulus when it was implanted into the medial basal hypothalamus. These findings demonstrate that DEX is a potent inhibitor of the suckling-induced PRL release. They also indicate that the site of action of DEX is not at the anterior pituitary gland or the paraventricular nuclei and hippocampus because DEX treatment and DEX implants had no effect on plasma PRL levels induced by DOMP and suckling stimulus, respectively. Our data suggest that the effect of DEX is mediated through a region of the medial basal hypothalamus. The observed transient block in suckling-induced PRL release may be physiologically relevant during stress in lactating mothers for conserving pituitary stores of the hormone needed for milk production or being able to adapt to a rapid change in osmoregulation.

Pituitary corticotrophs proliferate temporarily after adrenalectomy

Relationship of corticotroph proliferation answer and survival time after adrenalectomy was examined. Corticotroph proliferation rates were detected by short-term 3H-thymidine radiolabeling, then ACTH immunostaining and autoradiography. Effect of adrenalectomy on corticotroph proliferation rate was examined in vivo and an elevation was demonstrated first on the second postoperative day, increasing on the third-fourth day postoperatively and then decreasing. Effects of different secretagogues on corticotroph proliferation were examined in short-term pituitary monolayer cultures taken from ADX rats. CRF and Forskolin treatment potentiated corticotroph proliferation in cultures taken from adrenalectomized rats, but not in the controls. We suggest that croticotroph proliferation is stimulated via the cAMP-proteinkinase A pathway, while adrenalectomy plays a permissive role.

Reevaluation of the role of alpha 2-adrenoreceptors in morphine-stimulated release of growth hormone

The relationship between opioidergic and alpha 2-adrenergic system in the regulation of GH secretion was studied using a novel alpha 2-antagonist, CH-38083, and chronic treatment with yohimbine or clonidine. In male Wistar rats morphine (3 mg/kg s.c.), and clonidine (31 micrograms/kg i.p.) induced a significant increase in plasma GH levels. The pretreatment with the alpha 2-antagonist yohimbine (1 and 3 mg/kg) effectively inhibited the GH releasing effect or morphine and clonidine. CH-38083 at the dose of 1 mg/kg did not interfere with the morphine-induced GH secretion, while it fully antagonized the GH-releasing effect of clonidine. Higher doses (3 and 5 mg/kg) of CH-38083 only partly inhibited GH secretion induced by morphine. In rats chronically treated with clonidine (2 micrograms/ml in the drinking water for 14 days) the GH response to an injection of clonidine was blocked, while the effect of morphine on the GH secretion remained unchanged. In long-term castrated rats the effect of clonidine (15, 31 and 250 micrograms/kg i.p.) on the GH secretion was significantly blunted, while the GH-releasing effect of morphine (1, 3 and 5 mg/kg s.c.) remained unchanged. The replacement of testosterone (10 mg/kg for 4 days) in castrates restored the effect of clonidine, whereas it decreased the stimulatory action of morphine on the GH secretion. In rats chronically treated with yohimbine (2 mg/kg i.p. 2-3 times daily for 14 days until sacrifice), the GH response to a high dose of clonidine (0.5 mg/kg i.p.) was blocked, while the effect of morphine (5 mg/kg s.c.) was significantly enhanced.(ABSTRACT TRUNCATED AT 250 WORDS)

Corticotropin-releasing hormone-containing neurons in the hypothalamo-hypophyseal system in rats six weeks after bilateral lesions of the paraventricular nucleus

Corticotropin-releasing factor-like immunoreactive nerve fibers and varicosities are present in the pituitary stalk and median eminence 6 weeks after bilateral lesioning of the hypothalamic paraventricular nucleus. The total immunoreactivity may reach 10% of the control density. The origin of these fibers was investigated 3 days after hypothalamic transections in paraventricular-lesioned (6 weeks postoperatively) rats. Accumulations of corticotropin-releasing factor immunostaining were observed in the proximal portions of the transected axons and in neuronal perikarya. Fibers with retrograde labeling were seen lateral and dorsolateral from the sagittally oriented knife cuts which transected the retrochiasmatic area and cells were found in the supraoptic nucleus and in the perifornical nucleus (dorsal-dorsolateral to the fornix), ipsilateral to the lesion. No corticotropin-releasing factor immunostained cells were seen in other hypothalamic or preoptic nuclei which project to the median eminence or the posterior pituitary. Corticotropin-releasing factor containing cells in the supraoptic and perifornical nuclei may have an importance in stress response in rats with long-term paraventricular lesions.

Oligopeptides interfering with calcium channels inhibit prolactin and growth hormone release by cultured anterior pituitary cells of the rat

A number of oligopeptides, protected at their N termini and possessing an aldehyde residue at their C terminal amino acids, are able to inhibit 45Ca2+ influx into anterior pituitary cells grown in monolayer culture and depolarized with high extracellular potassium concentration. In addition, the same oligopeptides interfere with hormone release, especially with that produced by lactotrophs. Our findings imply that oligopeptides may represent a new class of calcium channel ligands, and the pituitary cells are sensitive targets for them.

The possible role of androgenic hormones in maturation of alpha-adrenergic mechanisms in the rat

Abstract In order to get better characterization of androgenic hormones on the functionality of the alpha(2)-adrenergic system and widen our previous studies, we investigated the effect of clonidine on the growth hormone (GH) secretion in male Wistar rats of various ages: 7-, 14- and 30-day old and adult, adult male castrated rats with and without testosterone treatment. Two different patterns of the GH response to clonidine have been observed in the control and testosterone-treated young animals: clonidine at the dose 15 mug/kg intraperitoneally had no effect on the GH secretion in 7- to 14-day old rat pups. In contrast, its effect appeared following the increase in the plasma testosterone concentration induced by pretreatment with testosterone (5 mg/kg subcutaneously for 4 days) in these animals. In 30-day old rats clonidine affected GH secretion and this influence was more pronounced in the testosterone-treated animals than in the controls. The decrease in the circulating testosterone levels caused by castration in adult male rats caused a decreased GH response to clonidine. Moreover, there was a tendency for the GH response to return in 4-week old animals. The effect of clonidine has been restored by testosterone replacement of castrates. Testosterone administration decreased basal plasma GH levels in the pups. However, it triggered the ultradian surges of GH secretion which were absent in the young animals. Clonidine had no effect on the corticosterone secretion in 7-day old animals. Testosterone treatment induced a response in the 7-day old rat and markedly potentiated its effect on the secretion of this hormone in 14- and 30-day old animals, respectively. Neither progesterone nor hydrocortisone influenced the GH-releasing effect of clonidine. Hydrocortisone markedly inhibited the basal- and clonidine-induced corticosterone secretion. The results of the present study indicate an important role of androgenic hormones in inducing and/or maintaining the effectiveness/sensitivity of the alpha(2)-adrenergic receptor system and suggest a possible role for the androgenic hormones in the maturation of alpha-adrenergic mechanisms in the rat.

Role of hypothalamic factors (growth-hormone-releasing hormone and gamma-aminobutyric acid) in the regulation of growth hormone secretion in the neonatal and adult rat

N-methyl aspartic acid (NMA) was without effect on the pituitary growth hormone (GH) secretion of adult and neonatal rats in vitro. Administration of NMA resulted in a rapid rise of plasma GH levels in intact but not in arcuate-nucleus-lesioned adult rats, indicating that NMA stimulated GH-releasing hormone (GRH) secretion. In 2-day-old rats, both NMA and gamma-aminobutyric acid (GABA) elevated plasma GH levels in a dose-related fashion; GRH administration was without effect. The elevation of plasma GH levels after NMA injection was reduced by administering an antibody to GRH. These results indicate that GH secretion is partly regulated by endogenous GRH in the newborn rat but that the elevation of plasma GH levels after GABA is not mediated by GRH. The high plasma GH levels seen in the newborn rat may result from the independent action of GABA and GRH but the effect of other factors cannot be excluded either.

Oxytocinergic neurons in rat hypothalamus. Dexamethasone-reversible increase in their corticotropin-releasing factor-41-like immunoreactivity in response to osmotic stimulation

Recent results have demonstrated altered corticotropin-releasing factor (CRF)-41 content of the neurointermediate lobe (NIL) of the pituitary gland in response to various manipulations including osmotic stimulation. This study was undertaken to determine whether changes in CRF-41 content of the NIL are accompanied by changes in intensity of CRF-41-like immunoreactivity (CRF-41-LI) of neurosecretory neurones of the hypothalamus in response to osmotic stimulation. Wistar rats of both sexes given either tap water ad libitum, 2% NaCl solution, or access to tap water was limited to 20 min daily, for 7 days. Subsets of rats from each group were adrenalectomized (ADX) or treated with dexamethasone (DEX). Thirty-six hour before perfusion with fixative consisting of buffered formaldehyde and picric acid, animals received 75 micrograms colchicine i.c.v. Forty micrometer thick vibratome sections were stained for CRF-LI, arginine vasopressin (AVP-LI) and oxytocin (OXY-LI) using the avidin-biotin-peroxidase complex method. In response to both types of osmotic stimulation magnocellular neurones of the paraventricular (PVN) and supraoptic nuclei (SON) showed increased CRF-LI, AVP-LI and OXY-LI, while CRF-LI of parvocellular perikarya of the PVN decreased. The enhanced CRF-LI seemed to appear in a subset of magnocellular neurones with OXY-LI but not AVP-LI. Increased staining intensities were also observed in magnocellular neurones in ADX rats challenged osmotically. In contrast, systemic DEX administration, as well as implantation of DEX in the area on the SON, sharply attenuated CRF-LI but not AVP-LI or OXY-LI of magnocellular neurones in osmotically stimulated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Prolactin response to immobilization stress and hemorrhage: the effect of hypothalamic deafferentations and posterior pituitary denervation

The roles of posterior and anterolateral connections to the mediobasal hypothalamus (MBH) as well as innervation of the posterior pituitary in the PRL response to immobilization (IMO) and hemorrhage (HEM) were studied by means of surgical isolation, performed 6-9 days before stress exposure. Male rats bearing indwelling tail artery cannulae subjected to 120-min IMO reached peak PRL secretion in 5-20 min. HEM of 25% elicited a significant rise of PRL levels. A posterior cut in the MBH, performed without damaging the serotonergic fibers from the brain stem, attenuated the PRL response to 25% HEM, whereas the PRL elevation due to IMO remained unaffected. An anterolateral cut around the MBH eliminated both the IMO- and HEM-induced stimulation of PRL. Posterior lobe denervation reduced by about 27% the PRL response to IMO and eliminated the response to HEM. These results suggest the following conclusions. The neural structures located posteriorly to the MBH are involved in the transfer of signals triggering PRL secretion due to hypovolemia. Intact anterolateral pathways to the MBH and stalk-median eminence region are essential for the PRL-releasing activity under both stimuli. The posterior lobe may be an important link in the PRL stress response in male rats.

The effect of systemically and locally administered steroids on VIP-like immunoreactive cells in the paraventricular nucleus of adrenalectomized rats

Seven days after adrenalectomy (ADX) the number of vasoactive intestinal peptide (VIP)- and corticotropin-releasing factor (CRF)-immunoreactive cells in the parvocellular part of the rat paraventricular nucleus (PVN) increased markedly. Dexamethasone in the drinking water (started immediately after ADX) or its local implantation around the hypothalamic PVN reduced the ADX-induced increase in the number of VIP- and CRF-like immunoreactive neurones. The present results suggest that PVN might be the site at which glucocorticoids inhibit the increase in VIP-positive cells after ADX.