EFFECTS OF PNEUMADIN (PNM) ON THE ADRENAL-GLANDS .3. EVIDENCE THAT ANANTAGONIST OF VASOPRESSIN RECEPTORS PREVENTS THE STIMULATING ACTION OF PNM ON STEROID-SECRETION OF RAT ADRENAL-GLAND

Pneumadin (PNM) is a decapeptide originally isolated from mammalian lu ngs, that exerts a potent antidiuretic effect due to stimulation of th e release of arginine-vasopressin (AVP). The effects of the administra tion for 1 or 2 days of 1.5 nmol/100g body weight of PNM, [Deamino-Pen (1), Val(4), D-Arg(8)]-AVP, an antagonist of AVP receptors (AVP-A), or PNM plus AVP-A on the rat pituitary-adrenal axis were investigated. P NM evoked a transient decrease in the ACTH plasma concentration, but i t strongly enhanced the blood levels of aldosterone and corticosterone . AVP-A alone did not induce conspicuous changes in the pituitary-adre nal axis function (except a significant rise in ACTH secretion), but i t completely reversed all the effects of PNM. These findings show that PNM exerts a notable adrenocortical secretagogue effects in rats, tha t is probably mediated by the peptide-induced increase in AVP release.