Antidiuretic Responses to Neurohypophysial Hormones and Some of Their Synthetic Analogues in Dogs and Rats

Abstract

The known neurohypophysial hormones and several synthetic analogues containing substituted amino acids in the side chain were injected intravenously into hydra ted dogs and rats. The nature of the amino acid in the penultimate position of the peptide side chain (the 8-position) appears to determine the relative antidiuretic activities of the peptides in dogs and rats. Substitution of lysine for 8-arginine reduces antidiuretic activity in dogs more than in rats. Analogues with an 8-leucine are weak in both dog and rat antidiuretic activities. Peptides containing an 8-arginine moiety cause more prolonged antidiuresis in rats than do their 8- lysine or 8-leucine counterparts. This is not due to differing rates of disappearance of these peptides from the circulation.