1 Synthetic analogues of oxytocin and of lysine-vasopressin with an hydroxyl group in either the L or D configuration replacing the primary amino group have been tested for biological activity. 2 [1-(L-2-Hydroxy-3-mercaptopropanoic acid)] oxytocin ([L-Hmp1]oxytocin) was 1.5 to 2 times more potent than oxytocin on the rat uterus in situ, the rat mammary strip and the rat mammary gland in situ and 3 times more potent on the rat isolated uterus.3 The pressor activity of [14L-2-hydroxy-3-mercaptopropanoic acid}8-lysine]vasopressin ([L-Hmp', Lys8] vasopressin) was 2.2 and the antidiuretic activity 2.1 times that of lysine-vasopressin. 4 The [D-Hmp'] analogues of oxytocin and vasopressin were much less potent than the analogues. 5 The responses to oxytocin and its hydroxy analogues in vivo were qualitatively indistinguishable but the pressor and antidiuretic responses to the hydroxy analogues of lysine-vasopressin were prolonged compared with those to the parent hormone. 6 The hydroxy analogues of oxytocin and lysine-vasopressin were not inactivated by pregnancy plasma oxytocinase. 7 The results are discussed in relation to the importance of the primary amino group for the biological activity and metabolism of the neurohypophysial hormones.
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