Effects of neurotensin and bombesin on the secretory and proliferative activity of regenerating rat adrenal cortex.

Neurotensin (NT) and bombesin (BM)-like peptides are known to be involved in the regulation of the rat hypothalamo-pituitary-adrenal axis. By using selective NT- and BM-receptor antagonists (NT-A and BM-A, respectively) we investigated whether endogenous NT and BM-like peptides play a role in the control of rat adrenal secretion and growth during enucleation-induced regeneration. At day 5 of regeneration, NT-A did not affect the plasma concentrations of aldosteronc (PAC) and corticosterone (PBC), but at day 8, it raised both PAC and PBC over the respective baseline value; the simultaneous administration of NT abolished this effect of NT-A. BM-A did not alter PAC and PBC at day 5 of regeneration, while at day 8 it enhanced PBC, an effect reversed by BM. NT-A did not alter mitotic index, and BM-A lowered it at both day 5 and day 8 of regeneration, an effect suppressed by the simultaneous administration of BM. Collectively, these findings allow us to draw the following conclusions: 1) endogenous NT and BM-like peptides influence adrenocortical regeneration in rats; 2) NT exerts a tonic inhibitory action on both aldosterone and corticosterone secretion, without affecting cell-proliferation rate; and 3) BM-like peptides exert a tonic suppressive effect on corticosterone production, coupled with a clear-cut stimulating effect on cell proliferation.     

Vasopressin pressor receptor-mediated activation of HPA axis by acute ethanol stress in rats

The plasma arginine vasopressin (AVP), ACTH, and corticosterone levels and the hypothalamic corticotropin-releasing hormone (CRH) content were measured after oral administration of 1 ml of 75% ethanol to rats, a model known to induce acute gastric erosions and stress. Elevated plasma AVP, ACTH, and corticosterone levels were detected 1 h after ethanol administration. Treatment with the vasopressin pressor (V(1)) receptor antagonist [d(CH(2))(5)Tyr(Me)-AVP] before ethanol administration significantly reduced the ACTH and corticosterone level increases. A higher hypothalamic CRH content was measured at 30 or 60 min after ethanol administration. V(1) receptor antagonist injection, 5 min before ethanol administration, inhibited the rise in hypothalamic CRH content. The protein synthesis blocker cycloheximide prevented the hypothalamic CRH content elevation after stress. The AVP-, CRH-, and AVP + CRH-induced in vitro ACTH release in normal anterior pituitary tissue cultures was also prevented by pretreatment with the V(1) receptor antagonist. The results support the hypothesis that stress-induced AVP may not only act directly on the ACTH producing anterior pituitary cells but also indirectly at the hypothalamic level via the synthesis and release of CRH.     

Effect of cyclooxygenase inhibitors on the CRH-induced pituitary-adrenocortical activity during crowding stress.

The aim of the present study was to determine the effect of social stress and significance of prostaglandins (PG) generated by constitutive and inducible cyclooxygenase (COX-1 and COX-2) in the stimulation of hypothalamic-pituitary-adrenal (HPA) axis by corticotropin releasing hormone (CRH) under basal and social crowding stress conditions. The stressed rats were crowded in groups of 24 to a cage for 3 or 7 days, whereas the control animals were haused in groups of 7 to a cage of the same size. The activity of HPA axis was determined by measuring plasma ACTH and serum corticosterone levels 1 h after i.p. CRH administration. Inhibitors of COX-1, piroxicam (0.2, 2.0, and 5.0 mg/kg), and COX-2, compound NS-398 (0.2 and 2.0 mg/kg), were administered i.p. 15 min prior to CRH (0.1 microg/kg i.p.) to control or crowded rats. The obtained results indicate that social stress for 3 and 7 days markedly intensifies the stimulatory action of CRH on ACTH secretion. Neither piroxicam nor NS-398 induce any significant effect on the CRH-elicited ACTH and corticosterone secretion in non-stressed or crowded rats. Therefore, PG generated by COX-1 or COX-2 do not participate to a significant extent in the stimulation of HPA axis by CRH under either basal conditions or during crowding stress. These results also indicate that the stimulatory action of CRH on ACTH secretion is not only completely resistant to desensitization but is sensitized during social crowding stress. The results contrast with a significant involvement of PG in the vasopressin-induced stimulation of HPA response during crowding stress.     

On the site of action of naloxone-stimulated cortisol secretion in gilts

The increase in serum cortisol concentrations following naloxone administration to female pigs was abolished by hypophysial stalk-transection, even though CRH and ACTH stimulated cortisol release in these animals. We suggest that the opioid antagonist enhances cortisol secretion primarily by a central action in pigs.     

中枢精氨酸加压素在大鼠促肾上腺皮质激素释放激素释放激素引起发热机制中的作用

实验对大鼠进行第三脑室和脑腹中隔区插管,用数字体温计测量大鼠的结肠温度,用放射免疫分析法测定脑中隔区精氨酸加压素（arginine vasopressin,AVP）含量,观察脑中隔区AVP在大鼠促肾上腺皮质激素释放激素（corticotrophin releasing hormone,CRH）性发热机制中的作用。结果发现：脑室注射CRH（5.0μg）引起大鼠结肠温度明显升高,同时明显增高脑中隔区AVP的含量。脑腹中隔区注射AVP V1受体拮抗剂本身并不导致大鼠结肠温度明显改变,但能显著增强脑室注射CRH引起的发热反应。而且,腹中隔区注射AVP显著抑制大鼠CRH性发热。结果提示：发热时CRH是引起脑腹中隔区AVP释放的因素之一,脑腹中隔区内源性AVP抑制中枢注射CRH引起的体温升高。     

Adrenocorticotrophin responses to hypoxaemia in fetal sheep are sustained in the presence of naloxone.

We have examined the effects of fetal hypoxaemia, produced by reducing the percent oxygen in maternal inspired air, on fetal plasma concentrations of corticotrophin releasing hormone (CRH), adrenocorticotrophin (ACTH) and cortisol and determined the effects of an opioid receptor antagonist, naloxone on these responses. Hypoxaemia (fetal PO2, 15-18 mmHg) for 60 min provoked a significant (P < 0.05) increase in fetal plasma ACTH and cortisol concentrations at days 125-130 of pregnancy, but did not affect circulating CRH. There was no effect of naloxone administered either intravenously (1.25 mg bolus followed by a 2.5 mg/h continuous infusion for one hour; fetal body weight approximately 2.5 Kg) or via the lateral cerebral ventricle (50 micrograms bolus followed by a 100 micrograms/h infusion for one hour) on this pattern of ACTH and cortisol change nor on the lack of CRH response to hypoxaemia. We conclude that the increase in fetal ACTH and cortisol in response to acute hypoxaemia is not accompanied by an increase in systemic CRH concentrations, nor is the response dependent on short-term opioid regulation.     

电场刺激对离体温育垂体前叶促肾上腺皮质激素分泌的影响

本实验应用离体温育大鼠垂体前叶组织块结合电场刺激及放射免疫测定方法,观察了垂体前叶内的神经纤维兴奋对促肾上腺皮质激素（ＡＣＴＨ）分泌的影响以及其它因素的作用。结果表明,一定参数的电场刺激使温育的大鼠四分之一垂体前叶组织块ＡＣＴＨ分泌增加,能被河豚毒素（ＴＴＸ）和藜芦碱部分阻断,此效应也可被地塞米松显著抑制,而同一参数的电场刺激与促肾上腺皮质激素释放激素（ＣＲＨ）诱发的ＡＣＴＨ分泌没有相互作用。经典神经递质受体阻断剂阿托品、心得安、酚妥拉明对电场刺激诱发的ＡＣＴＨ分泌没有显著影响;ＧＡＥＡ＿Ａ受体拮抗剂荷包牡丹碱明显促进此效应。该作用不受Ｐ物质拮抗剂ｓｐａｎｔｉｄｅ的影响,而降钙素基因相关肽（ＣＧＲＰ）受体拮抗剂ＣＧＲＰ片段８－３７能部分阻断这一作用。上述结果提示电场刺激所诱发的ＡＣＴＨ分泌可能部分由垂体前叶内ＣＧＲＰ能神经纤维介导。     

Nitric oxide mediates the interleukin-1beta- and nicotine-induced hypothalamic-pituitary-adrenocortical response during social stress.

We investigated the role of nitric oxide (NO) in the interleukin 1beta (IL-1beta) and nicotine induced hypothalamic-pituitary-adrenal axis (HPA) responses, and a possible significance of CRH and vasopressin in these responses under basal and social stress conditions. Male Wistar rats were crowded in cages for 7 days prior to treatment. All compounds were injected i.p., nitric oxide synthase (NOS) inhibitors, alpha-helical CRH antagonist and vasopressin receptor antagonist 15 min before IL-1beta or nicotine. Identical treatment received control non-stressed rats. Plasma ACTH and serum corticosterone levels were measured 1 h after IL-1beta or nicotine injection. L-NAME (2 mg/kg), a general nitric oxide synthase (NOS) inhibitor, considerably reduced the ACTH and corticosterone response to IL-1beta (0.5 microg/rat) the same extent in control and crowded rats. CRH antagonist almost abolished the nicotine-induced hormone responses and vasopressin antagonist reduced ACTH secretion. Constitutive endothelial eNOS and neuronal nNOS inhibitors substantially enhanced the nicotine-elicited ACTH and corticosterone response and inducible iNOS inhibitor, aminoguanidine, did not affect these responses in non-stressed rats. Social stress significantly attenuated the nicotine-induced ACTH and corticosterone response. In crowded rats L-NAME significantly deepened the stress-induced decrease in the nicotine-evoked ACTH and corticosterone response. In stressed rats neuronal NOS antagonist did not alter the nicotine-evoked hormone responses and inducible NOS inhibitor partly reversed the stress-induced decrease in ACTH response to nicotine. These results indicate that NO plays crucial role in the IL-1beta-induced HPA axis stimulation under basal and social stress conditions. CRH and vasopressin of the hypothalamic paraventricular nucleus may be involved in the nicotine induced alterations of HPA axis activity. NO generated by eNOS, but not nNOS, is involved in the stress-induced alterations of HPA axis activity by nicotine.     

Compound 48/80 inhibits neurotensin-induced hypotension in rats

The intravenous injection of neurotensin (NT) (0.4 and 1.1 nmoles/kg) produced dose-dependent hypotensive effects in pentobarbital anesthetized rats. The acute or chronic administration of compound 48/80, a well known mast cell depletor, completely abolished the hypotensive effect of low to medium doses of NT and unmasked the previously unknown hypertensive effect of high doses (4.0 nmoles/kg) of NT. This hypertensive effect was significantly reduced by infusing the animals with [D-Trp¹¹]-NT a selective antagonist of NT. The hypotensive action of NT in control rats was also significantly reduced by pretreating the animals with disodium cromoglycate, an antiallergic drug which is believed to stabilize mast cells membranes, or with a mixture of azatadine and methysergide. The results suggest the participation of histamine, serotonin and possibly other endogenous vasoactive substances, to the hypotensive action of NT in rats. The possible origin of these mediators is discussed.     

Evidence suggesting that ghrelin O-acyl transferase inhibitor acts at the hypothalamus to inhibit hypothalamo-pituitary-adrenocortical axis function in the rat

Production of n-octanoyl-modified ghrelin (GHREL), an active form of the peptide requires prohormone processing protease and GHREL O-acyltransferase (GOAT), as well as n-octanoic acid. Recently a selective GOAT antagonist (GO-CoA-Tat) was invented and this tool was used to study the possible role of endogenous GHREL in regulating HPA axis function in the rat. Administration of GOAT inhibitor (GOATi) resulted in a notable decrease in plasma ACTH, aldosterone and corticosterone concentrations at min 60 of experiment. Octanoic acid (OA) administration had no effect on levels of studied hormones. Plasma levels of unacylated and acylated GHREL remained unchanged for 60min after either GOATi or OA administration. Under experimental conditions applied, no significant changes were observed in the levels of GOAT mRNA in hypothalamus, pituitary, adrenal and stomach fundus. After GOATi injection hypothalamic CRH mRNA levels were elevated at 30 min and pituitary POMC mRNA levels at 60 min. Both GOATi and OA lowered basal, but not K(+)-stimulated CRH release by hypothalamic explants and had no effect on basal or CRH-stimulated ACTH release by pituitary slices. Neither GOATi nor OA affected corticosterone secretion by freshly isolated or cultured rat adrenocortical cells. Thus, results of our study suggest that in the rat endogenous GHREL exerts tonic stimulating effect on hypothalamic CRH release. This effect could be demonstrated by administering rats with selected inhibitor of ghrelin O-acyltransferase, the enzyme responsible for GHREL acylation, a process which is absolutely required for both GHSR-1a binding and its central endocrine activities.     

Effect of hypertonic saline on the corticotropin-releasing hormone and arginine vasopressin content of the rat pituitary neurointermediate lobe

The changes in the levels of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) in the neurointermediate lobe of the pituitary (NIL) following hypertonic saline administration were examined in rats. The plasma osmotic pressure in rats receiving 2% NaCl for 8 days was greatly increased. Plasma AVP concentration in rats receiving 2% NaCl for 8 days were significantly higher than in control rats (566% of the control level). Plasma corticosterone was significantly higher in the saline-treated rats than in controls, whereas plasma ACTH was not significantly different. The pituitary ACTH concentration was much higher in the saline-treated rats than in controls. CRH in the NIL was increased significantly by saline treatment (419% of the control concentration), whereas the CRH in the paraventricular nucleus and median eminence of control and saline-treated rats did not differ significantly. The AVP in the NIL fell greatly in saline treated rats. The extract from both control and saline-treated rats showed a major peak for immunoreactive CRH, with a retention time identical to that of rat CRH. However, the peak was much higher in the extract from saline-treated rats. The immunoreactive AVP peak was greatly reduced in saline-treated rats. These results suggest that hypertonic saline administration increases the CRH in the NIL and causes AVP hypersecretion and/or hyperfunction of magnocellular-NIL CRH might be responsible for pituitary-adrenal stimulation in saline-treated rats.     

Effect of adrenergic antagonists and cyclooxygenase inhibitors on the nicotine-induced hypothalamic-pituitary-adrenocortical activity.

Nicotine is a potent stimulus for the hypothalamic-pituitary-adrenal (HPA) axis. Systemic nicotine acts via central mechanisms to stimulate by multiple pathways the release of ACTH from the anterior pituitary corticotrops and corticosterone from the adrenal cortex. Nicotine may stimulate indirectly the hypothalamic paraventricular nucleus, the site of the corticotropin-releasing hormone (CRH) neurons which activates ACTH release. In the present studies an involvement of adrenergic system and prostaglandins synthesized by constitutive cyclooxygenase (COX-1) and inducible cyclooxygenase (COX-2) in the nicotine-induced HPA response in rats was investigated. Nicotine (2.5-5 mg/kg i.p.) significantly increased plasma ACTH and corticosterone levels measured 1 hr after administration. Adrenergic receptor antagonists or COX inhibitors were injected i.p. 15 min prior to nicotine and the rats were decapitated 1 hr after the last injection. Prazosin (0.01-0.1 mg/kg), an alpha1-adrenergic antagonist, significantly decreased the nicotine-evoked ACTH and corticosterone secretion. Yohimbine (0.1-1.0 mg/kg), an alpha2-adrenergic antagonist, moderately diminished ACTH response, and propranolol (0.1-10 mg/kg), a beta-adrenergic antagonist, did not significantly alter the nicotine-induced hormones secretion. Pretreatment with piroxicam (0.2-2.0 mg/kg), a COX-1 inhibitor, considerably impaired the nicotine-induced ACTH and corticosterone secretion. Compound NS-398 (0.2-5.0 mg/kg), a selective COX-2 blocker did not markedly alter these hormones secretion, and indomethacin (2 mg/kg), a non-selective COX inhibitor significantly diminished ACTH response. These results indicate that systemic nicotine stimulates the HPA axis indirectly, and both adrenergic system and prostaglandins are significantly involved in this stimulation. Noradrenaline, stimulating postsynaptic alpha1-adrenergic receptors, and prostaglandins, synthesized by COX-1 isoenzyme, are of crucial significance in the nicotine-induced ACTH and corticosterone secretion.     

Relationship between anorexigenic action of pituitary adenylate cyclase-activating polypeptide (PACAP) and that of corticotropin-releasing hormone (CRH) in the goldfish, Carassius auratus

Our recent research has indicated that intracerebroventricular (ICV) injection of pituitary adenylate cyclase-activating polypeptide (PACAP) suppresses food intake and locomotor activity in the goldfish. However, the anorexigenic mechanism of PACAP has not yet been clarified. The aim of this study was to investigate the relationship between the anorexigenic action of PACAP and that of corticotropin-releasing hormone (CRH), which is implicated in the regulation of energy homeostasis as a powerful anorexigenic peptide in the goldfish brain. We first examined feeding-induced changes in the expression of CRH mRNA, and the effect of ICV administration of PACAP on the expression of CRH mRNA in the goldfish brain. Semiquantitative analysis revealed that the expression of CRH mRNA was significantly increased by excessive feeding for 7 days. ICV administration of PACAP at a dose sufficient to suppress food intake induced a significant increase in the expression of CRH mRNA. We also examined the effect of alpha-helical CRH(9-41), a CRH antagonist, on the anorexigenic action of PACAP in the goldfish. The inhibitory effect of PACAP was completely suppressed by treatment with alpha-helical CRH(9-41). We finally investigated the effect of ICV-administered CRH on locomotor activity in the goldfish. CRH at a dose sufficient to suppress food intake induced a significant increase in locomotor activity, unlike ICV-injected PACAP. These results suggest that, in the goldfish, the anorexigenic action of PACAP is related to the CRH neuronal pathway, but that the modulation of locomotor activity by PACAP is independent of modulation by CRH.     

Effect of cyclooxygenase inhibitors on the vasopressin induced ACTH and corticosterone response during crowding stress.

The aim of the present study was to compare the effect of social stress on the corticotropin releasing hormone (CRH) and arginine vasopressin (AVP)-induced pituitary-adrenocortical activity. Also the significance of prostaglandins (PG) generated by constitutive and inducible cyclooxygenase (COX-1 and COX-2) in the stimulation of hypothalamic-pituitary-adrenal (HPA) axis by AVP under basal and crowding stress conditions was investigated. The control rats were housed 7 in a standard cage and stressed rats were crowded 24 in a cage of the same size during 7 days. The activity of HPA axis was determined by measuring plasma ACTH and serum corticosterone levels 1 h after i.p. AVP administration. Indomethacin (2.0 mg/kg i.p.), a non-selective COX inhibitor, piroxicam (0.2, 2.0, and 5.0 mg/kg), a more potent COX-1 than COX-2 inhibitor, and compound NS-398 (0.2 and 2.0 mg/kg) a selective COX-2 inhibitor, were administered i.p. 15 min prior to AVP (5.0 microg/kg i.p.) to control or crowded rats. The obtained results indicate that social stress for 7 days considerably inhibits the stimulatory action of AVP on ACTH secretion, while it intensifies the CRH-induced ACTH secretion. Indomethacin, piroxicam and NS-398 significantly diminished the AVP-elicited ACTH and corticosterone secretion in non-stressed rats. None of these COX antagonist induced any significant inhibition of the AVP-induced ACTH and corticosterone secretion in stressed rats. Therefore, PG generated by COX-1 or COX-2 do not participate to a significant extent in the HPA stimulation by AVP during crowding stress. These results suggest that social crowding stress desensitizes the PG stimulatory mechanism which considerably mediates the AVP-induced HPA stimulation under basal conditions. The results contrast with a lack of any involvement of PG in the CRH-induced stimulation of HPA response under basal or crowding stress conditions.     

Effect of L-NAME, a specific nitric oxide synthase inhibitor, on corticotropin-releasing hormone-elicited ACTH and corticosterone secretion.

This study was designed to determine the role of endogenous nitric oxide (NO) in the corticotropin-releasing hormone (CRH)-induced ACTH and corticosterone secretion, as well as possible involvement of hypothalamic dopamine and noradrenaline in that secretion in conscious rats. CRH given i.p. stimulated dose-dependently the pituitary-adrenocortical activity measured 1 h later. Dexamethasone (0.2 mg/kg i.p.) injected 1 h before CRH (1 microg/kg i.p.) totally abolished the CRH-elicited ACTH and corticosterone secretion, indicating a predominantly pituitary site of CRH-evoked stimulation. L-arginine (120 mg/kg i.p.) and N(omega)-nitro-L-arginine methyl ester (L-NAME 5-10 mg/kg i.p.) did not markedly affect the basal plasma ACTH and corticosterone levels. L-NAME given 15 min before CRH markedly, but not significantly, augmented the CRH-induced ACTH response, and enhanced more potently and significantly the corticosterone response. Pretreatment with L-arginine, a substrate for NOS, slightly diminished the CRH-induced ACTH response and considerably reduced the corticosterone response. L-arginine also significantly reversed the L-NAME-evoked increase in the CRH-induced ACTH and corticosterone secretion. L-NAME did not markedly alter the CRH-induced hypothalamic dopamine and noradrenaline levels, while L-arginine significantly increased noradrenaline level. However, those alterations were not directly correlated with the observed changes in ACTH and corticosterone secretion. These results indicate that in conscious rats NO plays a marked inhibitory role in the CRH-induced ACTH secretion and inhibits more potently corticosterone secretion. Hypothalamic dopamine and noradrenaline do not seem to be directly involved in the observed alterations in ACTH and corticosterone secretion.     

Behavioral and neuroendocrine actions of the Met-enkephalin-related peptide MERF

The effects and the mediation of the action of the proenkephalin derivative Met(5)-enkephalin-Arg(6)-Phe(7) (MERF) on the hypothalamo-pituitary-adrenal (HPA) system and open-field behavior were investigated in mice. Intracerebroventricular injection of the heptapeptide increased square crossing, rearing, and plasma corticosterone level. To characterize the receptors involved in these neuroendocrine processes, animals were pretreated either with the nonselective opioid antagonist naloxone or the kappa-antagonist nor-binaltorphimine (nor-BNI). Both antagonists dose-dependently attenuated the HPA activation elicited by MERF. Naloxone also blocked the behavioral responses, but nor-binaltorphimine did not elicit a significant inhibition. The dopamine antagonist haloperidol and a corticotropin-releasing hormone (CRH) antagonist were also preadministered to shed light on the transmission of the actions of MERF. Both the motor responses and the HPA activation were diminished by the preadministration of the CRH antagonist, while haloperidol attenuated only square crossing and rearing. To investigate the direct effect of MERF on the dopaminergic system, dopamine release of striatal slices was measured in a superfusion system. Neither the basal nor the electric impulse-evoked dopamine release was modified by MERF. The results suggest that opioid-mediation predominate in the neuroendocrine actions of MERF, and the effect of the heptapeptide on the HPA system seems to be mediated by kappa-receptors. In the behavioral responses evoked by MERF, both CRH release and the action of the dopaminergic neurons of the subcortical motor system might be involved. MERF also appears to activate the paraventricular CRH neurons, but dopaminergic transmission does not seem to play a significant role in its hypothalamic action.     

Somatostatin analogue (SMS 201-995) decreases plasma levels of corticotropin (ACTH) and corticotropin-releasing hormone in a patient with ectopic ACTH-producing tumors

Effects of long-acting somatostain analogue (SMS 201-995) on plasma corticotropin (ACTH) and corticotropin-releasing hormone (CRH) levels were studied in a patient (63-year-old woman) with ectopic ACTH-producing tumors associated with type I multiple endocrine neoplasia (MEN-I). The patient had undergone bilateral adrenalectomy. Plasma CRH, as well as plasma ACTH, beta-endorphin and alpha-MSH, increased. The hormone levels were dramatically decreased by acute administration of SMS 201-995. Moderately higher doses of dexamethasone (0.05 or 0.1 mg/kg a day) did not decrease plasma CRH or ACTH. An extremely high dose of dexamethasone (0.2 mg/kg a day), however, decreased plasma ACTH, but failed to decrease plasma CRH. Acute administration of SMS 201-995 further lowered the level of plasma ACTH even in this condition. In addition to the decrease in ACTH, SMS 201-995 decreased plasma CRH. Chronic administration of SMS 201-995 continuously decreased plasma CRH, ACTH and beta-endorphin. The decrease in these hormone concentrations accompanied the disappearance of hyperpigmentation. These results suggested that SMS 201-995 inhibits hypersecretion not only of ACTH but also of CRH, and that the agent is therapeutically useful in normalizing the hypersecretion of these hormones.     

Adrenocorticotropin administration increases testosterone secretion in adult male rats

It appears that the effect of acute administration of pituitary-adrenal hormones on the pituitary-gonadal axis is species-dependent. However, no information is available with regard to the effect of acute adrenocorticotropin (ACTH) administration on testosterone secretion in rats. The present data indicate that acute ACTH administration can increase serum testosterone levels without modifying luteinizing hormone (LH) levels. Since this rise was not observed in castrated rats, it must be assumed that increased serum testosterone was of gonadal origin. The action of ACTH on testosterone secretion was likely an indirect one since there is no evidence at present for a direct, short-term action of the pituitary-adrenal axis on Leydig cell function.     

Sex differences in morphine-induced analgesia of visceral pain are supraspinally and peripherally mediated

Increasing evidence suggests there is a sex difference in opioid analgesia of pain arising from somatic tissue. However, the existence of a sex difference in visceral pain and opioid analgesia is unclear. This was examined in the colorectal distention (CRD) model of visceral pain in the current study. The visceromotor response (vmr) to noxious CRD was recorded in gonadally intact male and female rats. Subcutaneous injection of morphine dose-dependently decreased the vmr in both groups without affecting colonic compliance. However, morphine was significantly more potent in male rats than females. Because systemic morphine can act at peripheral tissue and in the central nervous system (CNS), the source of the sex difference in morphine analgesia was determined. The peripherally restricted mu-opioid receptor (MOR) antagonist naloxone methiodide dose-dependently attenuated the effects of systemic morphine. Systemic administration of the peripherally restricted MOR agonist loperamide confirmed peripherally mediated morphine analgesia and revealed greater potency in males compared with females. Spinal administration of morphine dose-dependently attenuated the vmr, but there was no sex difference. Intracerebroventricular administration of morphine also dose-dependently attenuated the vmr with significantly greater potency in male rats. The present study documents a sex difference in morphine analgesia of visceral pain that is both peripherally and supraspinally mediated.     

The involvement of nitric oxide and prostaglandins in the cholinergic stimulation of hypothalamie-pituitary-adrenal response during crowding stress.

The aim of the present study was to determine the effect of social crowding stress and significance of nitric oxide (NO) and prostaglandins (PG) generated by constitutive and inducible nitric oxide synthase (NOS) and cyclooxygenase (COX) in the stimulation of hypothalamic-pituitary-adrenal (HPA) axis by cholinergic muscarinic receptor agonist carbachol. Inhibitors of neuronal NOS (nNOS) L-NNA, general NOS L-NAME and inducible NOS (iNOS) aminoguanidine, as well as inhibitors of COX-1, piroxicam, and COX-2, compound NS-398 were administered 15 min prior to carbachol to control or crowded rats (24 rats in cage for 7, during 3 and 7 days). In stressed rats L-NAME, L-NNA and aminoguanidine significantly intensified the carbachol-induced ACTH and corticosterone secretion, like in control rats. Piroxicam, markedly decreased the carbachol-induced ACTH and corticosterone response under either basal or stress conditions. Compound NS-398 did not markedly alter the carbachol-induced HPA response in control and stressed rats. Crowding stress (3 days) significantly impaired the i.c.v. prostaglandin E(2)-induced ACTH response. Corticotropin releasing hormone (CRH) receptor antagonists, alpha-helical CRH [9-14], given i.c.v. did not alter the PGE(2)-evoked corticosterone response in either control or stressed rats, indicating that hypothalamic CRH is not involved in the PGE(2)-induced central stimulation of HPA axis. In control rats L-NAME considerably enhanced, while L-arginine, a physiological NOS substrate, abolished the PGE(2)-induced ACTH and corticosterone response. In stressed rats this NOS blocker significantly increased and L-Arg reduced the stimulatory effect of PGE(2) on ACTH and corticosterone secretion. The carbachol-induced corticosterone response was significantly increased by pretreatment with nNOS inhibitor L-NNA and was considerably reduced by indomethacin, a general COX inhibitor. Pretreatment with both antagonists left the carbachol-induced corticosterone level unchanged, suggesting an independent and reciprocal effect of NO and PG in the cholinergic stimulation of pituitary-adrenocortical response. These results indicate that in the stimulatory action of muscarinic agonist, carbachol, NO is an inhibitory transmitter under basal and crowding stress conditions. This psychosocial stress does not functionally affect the NOS/NO systems. Prostaglandins are involved in the cholinergic muscarinic-induced stimulation of HPA response to a significant extent in non-stressed rats. PGE(2) may be involved in the carbachol-elicited HPA response under basal and stress conditions. Prostaglandins released in response to muscarinic stimulation did not evoke the hypothalamic CRH mediation. NO significantly impairs and PG stimulates the carbachol-induced HPA response in rats under basal and social stress conditions.