Relaxin inhibits myometrial activity in the ovariectomized non-pregnant ewe

Myometrial activity was abolished abruptly but reversibly in 4 out of 5 ewes by the intravenous injection of 1 mg (500 GPU) porcine relaxin. Recovery began only after about 90 min and was not complete until 3-4 h after the injection. During the relaxin-induced inhibition the myometrium responded to oxytocin administered intravenously in doses of 250 mU. One ewe received intrauterine infusions of 2.5 and 5.0 microgram PGF-2 alpha per min during the period of relaxin inhibition: the former dose evoked a slight, and the latter a marked, response from the myometrium. The rate of rise of intrauterine pressure and the mean amplitude of pressures cycles were significantly depressed at 1, 1.5 and 2 h after the relaxin injection.