Endocrinology
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Studies were performed to determine whether the isolated ovine anterior and intermediate pituitary might rhythmically secrete three POMC peptides, ACTH, ir-beta-endorphin (ir-beta-EP), and ir-alpha-melanocyte stimulating hormone (ir-alpha-MSH) in vivo. When blood was taken at 10-min intervals from four ewes with hypothalamo-pituitary-disconnection (HPD), a distinct POMC-peptide and cortisol ultradian rhythm was noted. A comparison of the four HPD ewes with five nonstressed hypothalamopituitary-intact (HPI) ewes revealed that the mean plasma levels of the three POMC-peptides and cortisol were increased, the mean ACTH and ir-alpha-MSH pulse amplitudes were increased, and the mean ir-beta-EP and ir-alpha-MSH interpulse intervals were decreased. ⋯ To determine whether the ACTH hypersecretion in the HPD ewe might reflect a net reduction in hypothalamic inhibitory influence over ACTH secretion, we examined the effects of dopamine (DA), somatostatin (SS-14), and rat atrial natriuretic peptide [rANF(1-28)] on the secretion of ACTH from cultured ovine anterior pituitary cells. DA and SS-14 did not exert a discernible effect on basal, CRF-, or arginine vasopressin (AVP)-stimulated ACTH secretion. Although basal ACTH secretion was unaffected by rANF(1-28) (10(-12)-10(-8) M), a significant inhibition of CRF- and AVP-stimulated ACTH release was observed.(ABSTRACT TRUNCATED AT 400 WORDS)