Comparison of the Pharmacologic Properties of Oxytocin and Its Highly Potent Analogue, Desamino-oxytocin

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Abstract
The pharmacologic properties of desamino-oxytocin, which differs from oxytocin only at the 1 position, where the free amino group in the half-cystine residue is replaced by hydrogen, are compared with those of oxytocin. It has been found that the free amino group is not required for manifestation of the biologic activities of oxytocin which are studied herein. Replacement of the amino group in the oxytocin molecule by hydrogen results in an enhancement of its avian depressor, rat oxytocic, and rat antidiuretic activities and a decrease in its rat pressor activity. Milk-ejecting activity in lactating rabbits is not appreciably affected. The patterns of response to equivalent units of oxytocin and desamino-oxytocin are practically identical. Increased antidiuretic and decreased pressor activities also occur upon replacement of the amino group in the 1 position of lysine-vasopressin with hydrogen to give l-desamino-8- lysine-vasopressin.