Studies of the regulation of the hypothalamic-pituitary adrenal axis in sheep with hypothalamic-pituitary disconnection. II. Evidence for in vivo ultradian hypersecretion of proopiomelanocortin peptides by the isolated anterior and intermediate pituitary

Abstract

Studies were performed to determine whether the isolated ovine anterior and intermediate pituitary might rhythmically secrete three POMC peptides, ACTH, ir-β-endorphin (ir-β-EP), and ir-α-melanocyte stimulating hormone (ir-α-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-α-MSH pulse amplitudes were increased, and the mean ir-β-EP and ir-α-MSH interpulse..