QUANTITATIVE COMPARISON OF SUBSTANCES RELATED TO OXYTOCIN: A NEW TEST

Abstract

A method is described for inducing labor in non-anesthetized rabbits on the 31st day of pregnancy by administering drugs with oxytocin-like activity. Use of the method permits a quantitative comparison and statistical evaluation to be made of the relative potencies of certain oxytocic substances. The method was applied to synthetic oxytocin (Syntocinon), natural oxytocin (Pitocin) and to valyl-oxytocin. The latter polypeptide was twice as potent as oxytocin when tested by this method compared with the activity determined by the standard blood pressure of the chicken or rat uterus in in vitro tests. Vasopressin (Pitressin) was inactive when assayed in non-toxic doses by this method. Methyler-gometrine (Methergin) induced labor in about 50% of animals tested, but only in doses within the toxic range.