The effect of cholecystokinin octapeptide on pituitary-adrenal hormone secretion.

The purpose of this investigation was to determine the influence of cholecystokinin octapeptide (CCK-OP) on pituitary-adrenal hormone secretion. CCK-OP at a dose of 5 microgram/kg (i.p.) elevated plasma corticosterone from 27 to 43 microgram/100 ml in one experiment and from 12 to 50 microgram/100 ml in a second experiment. Lower doses of CCK-OP (0.5 microgram/kg) elevated corticosterone from 12 microgram/100 ml to 20 microgram/100 ml. CCK-OP (1, 10, and 100 ng/ml) had no effect on ACTH-induced corticosterone released by isolated adrenal cells in vitro when tested in the presence of 50 pg of ACTH1-24. 100 and 500 ng of CCK-OP resulted in an increased pituitary ACTH release equal to 123% (n.s.) and a 206% (P less than 0.05) of control, respectively. In comparison, a 3/5 hypothalamic stalk median eminence equivalent increased ACTH release to 313% of control (P less than 0.05). The exact mechanism of this CCK effect on pituitary ACTH release is unknown. Although it is likely that the direct effects on the pituitary in vitro represent a pharmacologic and not a physiologic effect of this peptide, in vivo doses are between doses used for pancreatic effects and satiety effects suggesting that there may be a physiologic stimulating action of this peptide on the hypothalamic-pituitary-adrenal axis but at a level above the adrenal and pituitary.