抄録
In experiment with excised uterus strip of a rat, action of oxytocin was not inhibited by majority of amino acids constituting oxytocin and vasopressin but phenoltype compounds, such as nitrophenols, tyramine, and L-tyrosine ethyl ester, all inhibited the action of oxytocin competitively in 10-5 to 5×10-5g./cc. concentration. These had non-competitive inhibition on acetylcholine and barium chloride. Degree of dissociation and inhibitive power of phenol derivatives were approximately in direct proportion so that the active site of oxytocin was assumed to be in tyrosine in the oxytocin molecule.
Amine compounds like urethan, glycine ethyl ester, and methionine ethyl ester had no inhibitive action on oxytocin even in a high concentration of 10-4g./cc. and it was therefore assumed that the free amino group of cystine in the oxytocin molecule is not the active site. One of the phenol derivatives, estradiol, indicated competitive inhibition againt oxytocin in 10-6g./cc. concentiation.
