Lack of antagonism between thioglycerol and an oxytocin analogue not containing a disulphide bond.

1. The antagonistic effect of thioglycerol against oxytocin and an analogue of oxytocin not containing a disulphide bridge (desamino-1-carba-oxytocin) has been compared in the rat isolated depolarized uterus.2. Thioglycerol clearly differentiated between the two compounds, 40 mM producing a dose ratio of 12 with oxytocin but only 1.5 with the carba compound.3. It was confirmed that thioglycerol produces no appreciable destruction of oxytocin in vitro.4. The mode of action of thiols in antagonizing specifically S-S polypeptides is discussed. It is concluded that they probably do not produce their effect either by inactivating receptors or by inactivating S-S polypeptides in solution. A possible mechanism is that thiols potentiate the destruction of S-S polypeptides at the receptor site.