ACTH secretion from isolated hypophysial anterior lobes of male and female newborn rats: effects of corticotrophin-releasing factor, arginine vasopressin and oxytocin alone or in combination

Abstract

ACTH release by the anterior pituitary lobes of 8-day-old newborn rats (males and females) in the presence of rat corticotrophin-releasing factor (rCRF), arginine vasopressin (AVP) and oxytocin, given alone or in association, was measured in vitro. Rat CRF and AVP induced a dose-dependent release of ACTH in both sexes, while oxytocin was unable to stimulate ACTH secretion except at the highest dose tested. No sex-related difference was noted for any of the responses. Oxytocin (1 nmol/l) potentiated the response to rCRF (0.20 nmol/l) by the anterior pituitary lobes of females but not by those of males. This oxytocin potentiation was abolished when female newborn rats were injected at birth with testosterone (1 mg). AVP (1 nmol/l) alone stimulated ACTH release from the anterior pituitary lobes of the newborn rats of both sexes and markedly potentiated the ACTH response to rCRF. Although no difference between the sexes was noted for basal levels of AVP and oxytocin in the hypothalamus, the neurointermediate lobe and the peripheral plasma, the present data on the sex-related effect of oxytocin on the newborn adenohypophysis could, in part, explain why ACTH release in response to ether stress was previously reported to be more lasting in females than in males on day 8 postpartum.

Distribution of Corticotrophin‐Releasing Factor Type 1 Receptor‐Like Immunoreactivity in the Rat Pituitary

“…Ether exposure and immobilisation stimulate PRL secretion in male rats . A CRF antagonist, α‐helical CRF , has been shown to suppress immobilisation‐induced PRL release in the rat , and the CRF 1 antagonist CP‐154,526 has been shown to inhibit hypoxia‐induced PRL expression in the rat pituitary . Taken together with the results of the present study, this suggests that CRF stimulates PRL secretion through CRF 1 in lactotrophs during stress.…”

“…Furthermore, our previous study showed that female rats show more rapid and higher elevation of plasma ACTH than do male rats in response to footshock stress . However, no sex‐related difference is noted in the response to CRF of ACTH secretion from isolated anterior pituitary in vitro . Oestradiol causes a dysregulation of hypothalamic‐pituitary‐adrenal axis by inhibition of glucocorticoid feedback via oestrogen receptor acting at the level of the PVN .…”