The effect of relaxin on in vivo uterine electromyographic activity in the conscious ovariectomized ewe is oestrogen-dependent.

Electromyographic (EMG) activity of the uterus was recorded in vivo in 4 conscious ovariectomized ewes treated with oestrogen (one injection of 100 micrograms of oestradiol benzoate). Doses of 500 micrograms of purified porcine relaxin were injected intravenously 12, 16, 20, 24, 28 and 32 hrs after oestrogen treatment. Relaxin had an inhibitory effect on uterine activity between 16 and 32 hrs after oestrogen treatment. Because the period during which relaxin had a biological effect corresponded to the moment when oestrogen-induced uterine activity was maximal, it is suggested that the ability of relaxin to inhibit uterine activity in the ewe is oestrogen-dependent.