Pharmacological Studies on the Action of Relaxin upon KCl-Contracted Rat Uterus

Abstract

The pharmacological mechanism of the relaxing action of the ovarian hormone, relaxin, was studied in KCl-contracted rat uteri in vitro. Rat uterine segments were contracted by superfusion with a physiological solution in which 15% of the normal NaCl content was replaced by an equimolar amount of KCl. The effect of relaxin in reversing this contraction was achieved by a direct action upon the tissue and (.apprx. 45% at the concentration of relaxin used) by the liberation of endogenous catecholamines which relax the uterus via .beta.-adrenergic activity. The effect of relaxin was reduced by propranolol and it was not blocked by indomethacin, cimetidine or diphenhydramine. The effect of the ovarian peptide on uterine segments was potentiated in the presence of theophylline and indomethacin in the superfusing fluid. This effect of theophylline was insensitive to .beta.-adrenergic blockade. Evidently, relaxin relaxes the KCl-contracted rat uterus by a direct inhibitory action upon the uterine muscle and by facilitating the release of intramural catecholamines. Relaxin may act via the production of cAMP.