Uterine Size and Glycogen Content in Cycling and Pregnant. Rats: Influence of Relaxin

Abstract

Uterine weight and glycogen content were measured at stages of the estrous cycle and in the gravid and nongravid horns of unilaterally pregnant rats. The response of these parameters to administration of a purified preparation of porcine relaxin (relaxin B) was assessed during the estrus-diestrus interval and at Day 15 of gestation. Both uterine weight and glycogen content were greatest at proestrus and estrus and lowest at diestrus-1; when 0.1 mg of relaxin was administered beginning at estrus and injected over a 24 h period, the decline in uterine weight and glycogen was retarded. During gestation uterine weight declined prior to implantation and increased rapidly thereafter to a peak at Day 22 beyond which uterine size decreased through parturition. Uterine glycogen content followed similar increases except that the peak occurred on Day 23 and was sharply defined in advance of parturition at which time a rapid decline was observed. The increases in uterine weight and glycogen were significantly greater in the gravid horn than in the nongravid horn, and on the day of parturition both horns exhibited the highest glycogen concentration in the myometrium alone. Injection of relaxin at Day 15 of gestation increased uterine weight and glyco-gen content significantly in the myometrium of the nongravid horn without affecting the highly variable parameters in the gravid horn. Since uterine glycogen and tissue growth profiles parallel recently reported RIA relaxin concentrations in rats rather than changes in steroid hormone levels, these data suggest that relaxin may play a significant role in the uterine accommodation and glyco-gen storage which occur during late gestation