The effect of serotonin agonist 1-(trifluoromethylphenyl)-piperazine on corticotropin releasing factor and arginine vasopressin in rat hypothalamic nuclei

Effects of 1-(m-trifluoromethylphenyl)-piperazine, a serotonin agonist, were examined on rat plasma levels of adrenocorticotropin (ACTH) and arginine vasopressin (AVP), and on hypothalamic contents of corticotropin releasing factor (CRF) and AVP, to investigate the role of brain serotonin in ACTH regulation. Both plasma ACTH and AVP levels increased markedly 30 min after injection of the compound and were still elevated at 80 min. CRF and AVP contents in the median eminence decreased 30 min after injection but returned to the basal levels by 80 min. The AVP content in the supraoptic nucleus was elevated 80 min after injection. The CRF and aVP content did not significantly change in the paraventricular, suprachiasmatic and arcuate nuclei. Serotonin or 1-(m-trifluoromethylphenyl)-piperazine did not stimulate the release of ACTH in pituitary cell cultures. These results suggest that both CRF and AVP were secreted into the portal vessels by 1-(m-trifluoromethylphenyl)-piperazine to release ACTH from the anterior pituitary and that both the ACTH and AVP release were stimulated via the brain serotonergic mechanism.     

Plasma concentrations of adrenocorticotropin-related peptides in lambs injected with ovine corticotropin releasing factor or vasopressin

Synthetic ovine corticotropin-releasing factor (oCRF) and arginine vasopressin (AVP) were intravenously injected each alone or in combination (each peptide: 1 microgram/kg body weight) in lambs on days 1, 3, 7 and 20 after birth. Plasma samples were collected just before and 10 and 30 min after injection. Plasma concentrations of cortisol and aldosterone were measured. Adrenocorticotropin (ACTH)-related peptides were isolated by Sephadex G50 column chromatography and measured by radioimmunoassay. Three different peaks with an ACTH immunoreactivity were found in lamb plasma: a "big" ACTH molecular form (Mr = 30,000), an "intermediate" (Mr = 8000) and a "little" (Mr = 4500). In 1 and 3 days-old lambs, both CRF and AVP increased preferentially "intermediate" ACTH. In 7 and 20 days-old lambs, an increase in "little" ACTH occurred after CRF whereas "intermediate" ACTH rose after AVP. The rise in plasma levels of different molecular forms of ACTH after stimulation by CRF or AVP could suggest that the biological pathway of ACTH synthesis, storage and release may occur in different intracellular pools or rather in different pituitary cells. Intermediate ACTH stimulated adrenal secretion of cortisol as soon as the first day of postnatal life and increased plasma aldosterone concentration in 7 and 20 day-old lambs. At these stages aldosterone level did not change after a rise in "little" ACTH.     

新生大鼠下丘脑CRF和AVP神经元对急性低氧的应答

目的:观察肾上腺摘除新生大鼠下丘脑促肾上腺皮质激素释放激素(CRF)和精氨酸加压素(AVP)神经元对急性低氧的应答.方法:在低压氧舱中模拟高海拔低氧,用放免法测定AVP和CRP含量.结果:新生大鼠暴露于急性低氧环境下(模拟5 000 m和7 000 m海拔高度,24 h),其下丘脑CRP在3 d和7 d龄大鼠中无明显变化,但14d、21 d和28 d时低于对照;下丘脑AVP在3 d大鼠中亦无变化,但14 d时低于对照,7 d、21 d及28 d时高于对照.两者对低氧的应答模式随日龄而变化.摘除肾上腺后,14 d、21 d及28 d大鼠下丘脑CRF和AVP含量均显著低于同龄完整大鼠,此时暴露于急性低氧环境下,CRF和AVP无进一步的变化.结论:摘除肾上腺抑制下丘脑CRF和AVP的发育,影响它们对低氧应激的正常应答.     

Time course of vasopressin and oxytocin secretion after stress in adrenalectomized rats.

To characterize the participation of vasopressin (AVP) and oxytocin (OT) in hypothalamus-pituitary-adrenal regulation after adrenalectomy (ADX), we evaluated corticosterone, ACTH, AVP and OT plasma concentrations and AVP and OT content of the paraventricular nucleus (PVN) at different periods (3 h, 1, 3, 7 and 14 days) in sham or ADX rats under basal conditions and after immobilization stress. ADX animals showed undetectable corticosterone levels, while sham animals showed a marked increase in corticosterone and ACTH 3 h after surgery, then lowering to basal control levels. ADX rats showed high basal ACTH levels with a triphasic response without changes after immobilization. After three hours, the ADX group showed higher OT levels than the sham group. OT was increased after immobilization stress in sham and ADX groups. AVP plasma levels did not change throughout the basal or stress studies in either group. There was a decrease in hypothalamic AVP content 1 and 3 days after ADX under basal and stress conditions. Plasma osmolality showed a significant decrease in the ADX group at 3, 7, and 14 days. In conclusion, there are different pituitary-adrenal axis set points after removal of the glucocorticoid negative feedback. The role of vasopressinergic and oxytocinergic neurons in the ACTH secretion after ADX or immobilization stress appears to differ. Magnocellular AVP is unlikely to contribute to ACTH secretion in response to ADX or immobilization stress. On the other hand, OT is elicited by immobilization stress and might contribute to the ACTH secretion during short-term ADX.     

Central catecholaminergic control of ACTH secretion

Plasma adrenocorticotropic hormone (ACTH) has been measured after an intra-third ventricular administration of noradrenaline, an adrenergic agonist or an adrenergic antagonist. Centrally administered noradrenaline caused a significant increase in ACTH secretion. The alpha-agonist phenylephrine also increased the ACTH level. However, neither the alpha-antagonist phentolamine nor beta-agonist isoproterenol affected the ACTH level. The beta-antagonist propranolol evoked a significant elevation in ACTH. Passive immunoneutralization was examined with anti-rat corticotropin-releasing factor (CRF) rabbit serum, anti-arginine vasopressin (AVP) rabbit serum and normal rabbit serum (NRS) on the intra-third ventricular noradrenaline-induced ACTH secretion to study the involvement of endogenous CRF. An intra-third ventricular administration of noradrenaline caused a significant increase of ACTH levels in NRS-injected rats and anti-AVP-injected rats, whereas an i.v. anti-rat CRF injection significantly reduced the intra-third ventricular noradrenaline-induced ACTH secretion. These results suggest that central catecholamine stimulated ACTH secretion via the alpha-adrenergic mechanism and that endogenous CRF is at least partly involved in the noradrenaline-induced ACTH secretion.     

Role of arginine vasopressin in control of ACTH and LH release during stress

To determine the role of arginine vasopressin (AVP) in stress-induced release of anterior pituitary hormones, AVP antiserum or normal rabbit serum (NRS) was micro-injected into the 3rd ventricle of freely-moving, ovariectomized (OVX) female rats. A single 3 microliter injection was given, and 24 hours later, the injection was repeated 30 min prior to application of ether stress for 1 min. Although AVP antiserum had no effect on basal plasma ACTH concentrations, the elevation of plasma ACTH induced by ether stress was lowered significantly. Plasma LH tended to increase following ether stress but not significantly so; however, plasma LH following stress was significantly lower in the AVP antiserum-treated group than in the group pre-treated with NRS. Ether stress lowered plasma growth hormone (GH) levels and this lowering was slightly but significantly antagonized by AVP antiserum. Ether stress also elevated plasma prolactin (Prl) levels but these changes were not significantly modified by the antiserum. To evaluate any direct action of AVP on pituitary hormone secretion, the peptide was incubated with dispersed anterior pituitary cells for 2 hours. A dose-related release of ACTH occurred in doses ranging from 10 ng (10 p mole)-10 micrograms/tube, but there was no effect of AVP on release of LH. The release of other anterior pituitary hormones was also not affected except for a significant stimulation of TSH release at a high dose of AVP. The results indicate that AVP is involved in induction of ACTH and LH release during stress. The inhibitory action of the AVP antiserum on ACTH release may be mediated intrahypothalamically by blocking the stimulatory action of AVP on corticotropin-releasing factor (CRF) neurons and/or also in part by direct blockade of the stimulatory action of vasopressin on the pituitary. The effects of vasopressin on LH release are presumably brought about by blockade of a stimulatory action of AVP on the LHRH neuronal terminals.     

Corticotropin-releasing hormone and pituitary-adrenocortical responses in chronically stressed rats

Brain corticotropin-releasing hormone (CRH) concentration and pituitary adreno-cortical responses were examined in chronically stressed rats: body restraint stress (6 h/day) for 4 or 5 weeks. Stressed rats showed a reduction in weight gain. CRH concentration in the median eminence and the rest of the hypothalamus were not different between control and chronically immobilized rats. The anterior pituitary adenocorticotropic hormone (ACTH) concentration was elevated in chronically stressed rats, whereas plasma ACTH and corticosterone levels did not differ from the control values. The median eminence CRH concentration was reduced to the same extent at 5 min after onset of ether exposure (1 min) in chronically immobilized rats and controls. However, plasma ACTH and corticosterone showed greater responses to ether stress in chronically immobilized rats than in control rats. Plasma ACTH and corticosterone responses to exogenous CRH were not different between control and chronically immobilized rats, while the response to arginine vasopressin (AVP) was significantly greater in chronically immobilized rats. These results suggest that chronic stress caused an increase in the ACTH-secreting mechanism and that pituitary hypersensitivity to vasopressin might at least be partly responsible for this.     

Immunoreactive delta sleep-inducing peptide in the rat hypothalamus, pituitary and adrenal gland: effects of adrenalectomy

Immunoreactive (IR) delta sleep-inducing peptide (DSIP) was examined by immunocytochemistry in the rat pituitary and adrenal gland and found to be colocalized with IR thyroid-stimulating hormone in the pituitary and with noradrenaline in the adrenal medulla. IR-DSIP was also detectable in nerve fibers in the posterior pituitary. By radioimmunoassay, IR-DSIP was quantified in plasma and tissue extracts after uni- or bilateral adrenalectomy. Significantly elevated plasma levels of IR-DSIP were measured 5 days after bilateral adrenalectomy (p less than 0.001). IR-DSIP was increased (p less than 0.05) in pituitary extracts from bilaterally adrenalectomized rats after 5 days, but not after 14 or 28 days. Sham- and unoperated animals did not significantly differ in plasma or tissue concentration of IR-DSIP. High-performance liquid chromatography of C18 SEP-PAK purified hypothalamus extracts revealed a single peak of IR-DSIP material of lower hydrophobicity than synthetic DSIP. The elevated concentration of IR-DSIP in the rat pituitary and plasma after bilateral adrenalectomy is consistent with the previously suggested role of DSIP to influence the activity of the hypothalamic-pituitary-adrenal axis.     

Effects of lithium on the hypothalamo-pituitary-adrenal axis

The effect of lithium on the hypothalamo-pituitary-adrenal axis was studied in vivo and in vitro. The levels of plasma vasopressin, ACTH and corticosterone increased after the administration of lithium (LiCl 4 mmol/kg BW, 11 days) in rats, while the tissue vasopressin concentration in the median eminence, the rest of the hypothalamus and the posterior pituitary was decreased. The CRF concentration in the posterior pituitary increased markedly, but it did not change significantly in the median eminence or the rest of the hypothalamus. The elevated plasma ACTH level might be at least partly due to the increased vasopression secretion. Lithium stimulated ACTH secretion per se and also enhanced vasopressin-induced ACTH secretion in cultured pituitary cells and in half pituitary incubations, while it did not affect CRF-induced ACTH secretion. Lithium inhibited CRF-induced cAMP accumulation in half pituitary incubations, while lithium and vasopressin did not affect cAMP accumulation per se or even when administered together. The results suggest that lithium-induced ACTH release is via a cAMP-independent mechanism. Thus, it is possible that lithium stimulates ACTH release by acting directly on the corticotroph, stimulating vasopressin release and potentiating vasopressin-induced ACTH release.     

Pituitary and adrenal responses to ovine corticotropin releasing factor and vasopressin injected into young and adult guinea-pigs

Comparison of effects of synthetic ovine corticotropin releasing factor (oCRF), Arginine-Vasopressin (AVP) and the combination of both peptides have been tried in adult and 7-days-old guinea-pigs. On plasmas collected 15 min after interscapulary injection, cortisol, aldosterone and ACTH were measured. The different circulating forms of ACTH were isolated by Sephadex G50 column chromatography, with 1% formic acid and measured by radioimmunoassay. Thus, in the guinea-pig plasma, we detected three immunoreactive forms of ACTH: a "big" molecular form (Mr greater than 20000), an "intermediate" (Mr = 9500) and a "little" ACTH form (Mr = 4500) which was eluted in the same fractions as human 1-39 ACTH. In adult guinea-pigs, CRF increased total ACTH and the "intermediate" form and also plasma cortisol concentrations whereas AVP remained without significant effect excepted a rise in cortisol levels. Injected together, CRF and AVP enhanced plasma concentrations of total ACTH, of the three circulating forms and of cortisol. In 7-days-old guinea-pigs, both CRF and AVP increased plasma concentrations of total, of "intermediate" ACTH and of cortisol and aldosterone whereas the combination of both peptides enhanced dramatically plasma concentration of total ACTH suggesting a magnifying effect of AVP on CRF activity still more efficient in young than in adult guinea-pigs.     

In vivo and in vitro release of ACTH by synthetic CRF

The 41-residue corticotropin releasing factor (CRF) was synthesized by the solid phase method. The synthetic CRF and arginine vasopressin (AVP) were examined for ACTH releasing activity and effects on the release of 5 other pituitary hormones in vivo and in vitro. Injection of the CRF into pharmacologically blocked rats increased plasma corticosterone levels in a dose-related manner. The minimum effective dose was 1.6 x 10(-12) mol/100 g body weight. CRF also significantly stimulated release of ACTH-like immunoreactivity in a dose-related manner from rat pituitary quarters beginning at a concentration of 10(-9) M. AVP, a peptide known to have CRF activity, exhibited slightly lower corticotropin releasing activity than the CRF at equimolar dose levels. Secretion of other pituitary hormones was not appreciably altered by either the CRF or AVP.     

Glucocorticoids regulate peptidyl-glycine alpha-amidating monooxygenase gene expression in the rat hypothalamic paraventricular nucleus

Peptidyl-glycine alpha-amidating monooxygenase (PAM) is a posttranslational processing enzyme which catalyzes the formation of biologically active alpha-amidated peptides. The two major neuropeptides involved in the regulation of ACTH secretion [CRF and arginine vasopressin (AVP)], synthesized in the parvocellular part of the hypothalamic paraventricular nucleus (PVN), are amidated, and their synthesis and/or release is negatively regulated by glucocorticoids. In this study, using in situ hybridization, we have shown that PAM mRNA is abundantly expressed in the hypothalamic paraventricular and supraoptic nucleus. Surgical adrenalectomy (ADX) induced increases in PAM, CRF, and AVP mRNA in the parvocellular part of the PVN, while corticosterone treatment normalized these values. PAM and AVP gene expression were not changed in the magnocellular part of the PVN or in the supraoptic nucleus. These observations suggest that in addition to stimulation of CRF and AVP synthesis, ADX induces an increase in PAM synthesis in the PVN and, thus, support the hypothesis of increased secretion of both CRF and AVP after ADX.     

Cortisol responsiveness to insulin-induced hypoglycemia in Cushing's syndrome with huge nodular adrenocortical hyperplasia

A 51-yr-old male patient with a 3 yr history of Cushing's syndrome is described. The baseline plasma cortisol level was elevated, while the plasma ACTH levels remained at an undetectable level. Dynamic testing of pituitary-adrenal function revealed no suppression after 8 mg of dexamethasone, and there was no response to metyrapone or CRF, while plasma cortisol showed a hyperresponse to synthetic ACTH. Plasma cortisol responded to insulin-induced hypoglycemia without an obvious ACTH response. These and the computerized tomography data suggested a "huge" bilateral nodular adrenocortical hyperplasia which was later confirmed by surgery. The left and right adrenal glands weighed 55 and 76 g, respectively. In vitro experiments, using the adrenal tissue, showed that there was an adrenal cortisol response to 1-39 ACTH but not to regular insulin, arginine vasopressin, angiotensin II, norepinephrine or epinephrine. These results indicate that plasma cortisol responded to a slight hypoglycemia-induced plasma ACTH change which was not detected in the ACTH radioimmunoassay or to factors other than ACTH which might be induced by hypoglycemia.     

Estrogen and androgen influence hypothalamic AVP and CRF concentrations in fetal and adult sheep

The present study tested the hypothesis that action of sex steroids on the hypothalamus-pituitary-adrenal (HPA) axis is measurable in the hypothalamus. Late-gestation fetal sheep were treated (5 mg/21 days) with either estradiol, androstenedione, or tamoxifen and compared to age-matched control fetuses. Tamoxifen significantly increased hypothalamic corticotropin releasing factor (CRF) and arginine vasopressin (AVP) concentrations, and androstenedione significantly decreased hypothalamic CRF concentration. Adult sheep were treated with estrone (10 mg/21 days), and responded with significant increases in hypothalamic AVP concentration, but not in immunoreactive ACTH concentration or processing within the pituitary. The results demonstrate that the effect of estrogen on the HPA axis is measurable in the hypothalamus, and is therefore not primarily at the anterior pituitary.     

Effects of experimental hypothyroidism on the development of the hypothalamo-pituitary-adrenal axis in the rat

Hypothyroid pups were obtained by adding methimazole in the mother's drinking water from day 15 of gestation and sacrificed at 4, 8 or 15 days. Circulating corticosterone decreased at all ages, while CBG concentrations diminished at day 4, increased at day 8 and did not change at day 15 in hypothyroid rats. As opposed to controls, plasma ACTH concentrations decreased steadily with age while there was an accumulation of ACTH in the anterior pituitary of hypothyroid 15-day-old rats. Anterior pituitary POMC contents were unaffected by the treatment. In the hypothalamic PVN, CRF mRNA levels in the total population of CRF-synthesizing cells and in the CRF+/AVP+ subpopulation were below those of controls whatever the age considered while AVP mRNA in the CRF+/AVP+ subpopulation did not change at day 4 and decreased at day 8 and 15 in hypothyroid animals. Both the number of cell bodies expressing detectable levels of CRF mRNA and the percentage of CRF and AVP colocalization decreased at day 4 and were unchanged thereafter. CRF and AVP immunoreactivity in the zona externa of the median eminence increased with age but was not affected by methimazole treatment. The concentration of AVP mRNA in the magnocellular cell bodies of the PVN and the SON as well as AVP immunoreactivity in the zona interna of the median eminence were not changed by the treatment at days 4 and 8. In hypothyroid 15-day-old rats, SON AVP mRNA increased, AVP immunoreactivity decreased while plasma osmolality was enhanced. In conclusion, our data demonstrate that experimental hypothyroidism impairs specifically the maturation of hypothalamic parvocellular CRF and AVP gene expression during the stress hyporesponsive period. These observations suggest that the physiological peak in plasma thyroxine concentrations that occur between day 8-12 may participate in the maturation of hypothalamic CRF- and AVP-synthesizing cells.     

Upregulation of CRH gene expression and downregulation of arginine vasopressin gene expression in the hypothalamus of bilateral nephrectomized rats

The expression of the corticotropin-releasing hormone (CRH) gene and the arginine vasopressin (AVP) gene in the hypothalamus examined in bilateral nephrectomized rats by in situ hybridization histochemistry. The expression of the CRH gene was significantly increased in the parvocellular part of the paraventricular nucleus (PVN) 12 and 20 h after bilateral nephrectomy in comparison with that after sham operation. The plasma concentration of adrenocorticotropic hormone (ACTH) in nephrectomized rats was significantly higher than that in sham operated rats 20 h after surgery. In contrast, the expression of the AVP gene in both the parvocellular and magnocellular parts of the PVN and throughout the supraoptic nucleus (SON) was significantly decreased 20 h after bilateral nephrectomy in comparison with that after sham operation. These results suggest that nephrectomy-induced upregulation of the CRH gene with elevation of plasma ACTH may be due to the activation of the hypothalamo-pituitary adrenal (HPA) axis.     

Osmotic stimulation affects neurohypophysial corticotropin releasing factor-41 content: effect of dexamethasone

In this study we examined the effects of 2% saline loading (S), partial restriction of water consumption (R) or a combination of S or R with dexamethasone (DEX) treatment for 14 days on corticotropin releasing factor (CRF)-41 content of the neurointermediate lobe (NIL) and supraoptic nuclei (SON) of male Wistar rats. Arginine vasopressin (AVP) and oxytocin (OXY) contents of the NIL and SON were also assayed as well as plasma corticosterone, ACTH, [Na+] and [Cl-] concentrations. S or R for 14 days resulted in an increase in CRF-41 content and a concomitant drop in AVP and OXY contents of the NIL. Dexamethasone treatment enhanced the effect of S but not of R on NIL CRF-41 content. Dexamethasone treatment abolished the decrease in the AVP content and partially reversed the decrease in the OXY content of the NIL in response to S but not in response to R. No changes were observed in CRF-41, AVP and OXY content of the SON. Unstressed plasma corticosterone concentrations were not changed in S rats but were elevated in R rats; DEX did not prevent this elevation. Plasma ACTH concentrations were low in all groups examined. Plasma [Na+] and [Cl-] increased in response to both S and R. Increases in [Na+] and [Cl-] evoked by S but not R were prevented by DEX treatment. The results show that in the NIL, osmotic stimulation decreases AVP and OXY content, while it increases the CRF-41 content.     

Continuous central vasopressin infusion increases peripheral fetal corticotropin and cortisol in the fetal sheep

In previous studies on regulation of fetal adrenocorticotropin (ACTH) secretion, corticotropin releasing factor (CRF) and arginine vasopressin (AVP) have been administered by peripheral intravascular infusion. In order to look at an alternate route of administration, we investigated the effect of continuous intracerebroventricular administration of AVP to the fetus on fetal plasma ACTH and fetal and maternal plasma cortisol concentrations. Sheep fetuses (n = 9) were instrumental with carotid artery and lateral cerebral ventricular catheters. Fetuses were given intracerebroventricular infusion from 125-134 days gestational age of artificial cerebrospinal fluid vehicle (n = 4), or AVP 250 mu U.min-1 continuously in artificial cerebrospinal fluid vehicle (n =5). Fetal blood was obtained daily between 09.00 and 12.00h and 20.00 and 23.00h. Over the infusion period, fetal plasma ACTH and cortisol concentrations in AVP infused fetuses increased (P less than 0.05) compared with the vehicle infused group. Gestation length for the fetuses in the AVP and vehicle infused groups were 139 +/- 4.9 (n =4) and 145 +/- 4.6 (n = 3) days respectively (n.s.). Fetal plasma AVP concentrations in the AVP infused group were not different from the vehicle infused group.     

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.