Abstract
Carbobenzoxylated peptides containing tyrosine inhibited competitively the action of oxytocin on the isolated rat uterus. Among these peptides carbobenzoxy-L-tyrosyl-L-tyrosinate was the most active and 30.4 times as potent as p-nitrophenol on the molar basis. This peptide had non-competitive inhibitions to ACh and barium chloride, but had more active and competitive antagonism to oxytocin when assayed by using their doseresponse curves. On the other hand, it had no inhibition to the avian depressure by oxytocin and to the raising blood pressure by vasopressin. Di-carbobenzoxy-L-cystinyl-di-L-tyrosine ethyl ester, having a low activity for inhibition of contraction by oxytocin, inhibited about 50 per cent of avian depressure by oxytocin, and almost inhibited the raising blood pressure by vasopressin in dog and rabbit.
