Pharmacologic Activities of the 8-Citrulline Analogues of Oxytocin and Vasopressin

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Abstract
The activities of the 8-citrulline analogues of oxytocin and vasopressin were compared with 3 natural hormones: oxytocin, arginine vasotocin and arginine vasopressin. The substitution of citrulline for the 8-leucine in oxytocin reduces oxytocic and milk-ejecting activities with some increase in vasopressor and antidiuretic activities, which, however, are far lower than those of arginine vasotocin. If citrulline replaces the 8-arginine of arginine vasopressin, vasopressor and antidiuretic activities are not more than one tenth of that of arginine vasopressin. The oxytocic response to both analogues is enhanced in the presence of magnesium ions. Only arginine vasotocin has a very high potency in increasing the permeability of the isolated frog bladder. The citrulline analogues, in comparison with arginine vasopressin, have a short half-life of activity in antidiuretic assays in the rat.