Effects of oxytocin antagonists on the saluresis accompanying carotid occlusion

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Abstract
Synthetic analogues of oxytocin and vasopressin antagonistic to the action of the parent molecules were infused into chloralosed cats. Three of these (2-O-methyltyrosine oxytocin, 2-O-ethyl-tyrosine oxytocin and 2-p-ethylphenylalanine oxytocin) were per se only slightly pressor and did not change base-line salt excretion. They completely and reversibly inhibited the saluresis-but not the accompanying rise in arterial pressure-associated with short periods of carotid occlusion. These same analogues also completely and reversibly inhibited the pressor effects of single iv doses of vasopressin and oxytocin, but the saluretic effect only of injected oxytocin was eliminated. The size (as opposed to polarity or chemical activity) of the p-phenyl substituent of the 2-position amino acid in oxytocin would appear to determine the difference between agonistic and antagonistic receptor interaction on the basis of steric permissance or hindrance. It is suggested from these results that the saluretic factor present in jugular vein plasma during carotid occulsion is chemically related to, but probably not identical with, oxytocin, and originates in the posterior hypothalamus.