Absolute oxytocic potencies of highly purified neurohypophysial hormones and analogues were determined on isolated rat uteri suspended in van DykeHastings solution. Assays were performed in bath solutions with and without magnesium ions. In a concentration of 0.5 raM/1. magnesium ions were found to augment the response to the U.S.P. Standard, oxytocin, lysine and arginine vasopressins and all the analogues tested, but there was considerable variation between substances in the degree to which this potentiation occurred. Advantages inherent to the solution of van Dyke and Hastings are discussed, and reasons are presented for utilizing this solution without magnesium for assays of oxytocin and posterior pituitary extracts.

The pattern of pharmacological activities in the chicken ncurohypophysis has been studied and described. These activities correspond to those of a mixture of oxytocin and arginine vasotocin, an analogue of oxytocin synthesized by Katsoyannis and du Vigneaud. Paper chromatographic and enzymatic studies, together with the demonstration of inactivation by thioglycollatc, furnish additional evidence suggesting that oxytocin and arginine vasotocin may be neurohypophysial hormones in the chicken, Galhis domesticus. P RESSOR and diuretic responses to the intravenous injection of chickenposterior pituitary extracts were originally demonstrated by Herring in 1908 (1). Mackenzie (2) found that such extracts also had potent galactogogue (milk-ejection) activity. Antidiuretic and oxytocic activities in extracts of fowl posterior pituitaries were first demonstrated by de Lawder, Tarr and Geiling (3), and Geiling subsequently reported that these activities were about one-half as strong as those present in U.S.P. Posterior Pituitary Powder (4). Frog water-balance activity was first described in the bird pituitary by Heller (5). Water-balance activity was far greater than in mammalian extracts of equivalent oxytocic and antidiuretic potency.Detailed pharmacological and chemical studies of neurohypophysial hormones from vertebrates other than mammals have not been reported. In the present study we used manifold assays, chromatography and inactivation by trypsin and thioglycollate to characterize neurohypophysial hormones of the domestic chicken.

No abstract

No abstract

No abstract