THE EFFECT OF PROLONGED ADMINISTRATION OF RELAXIN ON SOME FUNCTIONAL PROPERTIES OF THE NON-PREGNANT MOUSE AND RAT UTERUS

Abstract

Motility and tone of the non-pregnant rat and mouse uterus were studied in vitro and in vivo as influenced by relaxin. In the in vitro experiments the following functional qualities were recorded: frequency, mean amplitude, uterine work (total amplitude × load applied to the frontal writing levers), tone. The in vivo experiments included: recording of the spontaneous uterine motility in rats at a low constant intrauterine pressure. volume-pressure curves from the rat uterus by using a constant infusion devise and a strain gauge pressure transducer. Uterine work of the mouse uterus in vitro after a single subcutaneous injection of relaxin in saline was markedly reduced for a period of one hour but reached normal values 3–6 hours after the injection. The motility inhibiting effect could also be elicited by subcutaneous injection of relaxin in repository suspension. Frequency, mean amplitude, uterine work and tone of the oestradiol-progesterone pretreated rat uterus in vitro was not significantly altered after prolonged administration of relaxin in a repository suspension. Uterine sensitivity to oxytocin in vitro and in vivo was not definitely influenced by prolonged action of relaxin. Uterine distensibility, as evaluated from volume-pressure curves, was markedly enhanced after prolonged pretreatment with relaxin. It is suggested that the increased distensibility may be due to the hypertrophy of the uterus induced by relaxin but also an actual modification of its functional properties in this respect. The necessity of distinguishing the immediate motility inhibiting effect of relaxin from prolonged action of this substance on the uterus is emphasized.