Potentiation of Oxytocin and Prostaglandins-Evoked Responses by ( + ) Inpea on Isolated Rat Uterus: Its Specificity and Selectivity

Abstract

Abstract-The effect of (-{-) INPEA on various stimulant drugs was examined on isolated rat uterus. Addition of (;) INPEA (1 > 10-5 g/ml) to the organ bath, pro duced marked potentiation in the contractile responses of oxytocin and prostaglan dins. Potentiation was less significant to 5-HT, vasopressin, angiotensin and brady kinin. (-) INPEA did not potentiate the responses of oxytocin on isolated rat mam mary strip and the responses of prostaglandins on rat stomach (fundus) strip, guinea pig tracheal chain and guinea-pig ileum. The significance of these findings has been discussed.(_') INPEA (1-4'-nitrophenyl-2-isopropyl aminoethanol) hydrochloride, an adre nergic beta receptor blocking agent has been clinically evaluated in angina pectoris and cardiac arrhythmias and was shown to be effective (1, 2). Its beta blocking effect has been reported to be considerably less than the reference beta blocker, propranolol (3).While studying the pharmacological properties of INPEA, Saini and Sharma (4) observed a marked difference in the pharmacological activity between its optical isomers. Both In the present study' a number of uterine stimulants and a number of tissues respon sive to oxytocin or prostaglandins were used to investigate the specificity and selectivity respectively, if any, of the (=) INPEA-induced potentiation. MATERIALS AND METHODS Specificity of (-'-) INPEA-induced potentiationThe potentiating effect of (-!-) INPEA on the contractile responses evoked by various agonists was studied on isolated rat uterus preparation, as described by Holton (7). Oest rus induced rats (oestradiol dipropionate 200 ,ug, s.c., 15 hr prior to starting the experiment)of Charles-Foster strain weighing 150-200 g were used. The animals were stunned by a blow on the head and a small piece (2 cm) of the cervical end of the uterine horn was re moved and suspended in an organ bath (10 ml) containing de Jalon's solution (9 g NaCI,