SUMMARY
A study was made of the effects of both systemic and intrauterine progesterone and medroxyprogesterone acetate (MPA) administration on the duration of pregnancy in the guinea-pig. In no case was pregnancy prolonged beyond normal term. When progesterone and MPA were administered to non-pregnant guinea-pigs (in doses up to 50 times that required to block myometrial activity in the rabbit) there was no effect on the amplitude and frequency of intrauterine pressure cycles recorded in vivo by means of intrauterine balloons. The response of the uterus to a standard dose (20 m-u.) of oxytocin was unchanged by progesterone. The administration of progesterone by an intrauterine, instead of a systemic, route did not alter the result. It is concluded that progesterone is not a myometrial blocking agent in the guinea-pig.
Summary. Theca and granulosa layers were isolated from the preovulatory follicles of prepubertal gilts which were untreated (Group A), killed 72 h after 1000 i.u. PMSG (Group B), killed 84 h after PMSG (Group C), or killed 84 h after PMSG + 500 i.u. hCG given at 72 h (Group D). The tissues from individual follicles were cultured for 24 h alone (C), with FSH (F) or with LH (L), and the content of immunoreactive relaxin in the culture media was measured by RIA. Concentrations of relaxin-like material were close to the limit of detection of the assay in all granulosa cell cultures, and in the thecal cultures from the untreated gilts. However, thecal cultures from all 19 treated gilts produced relaxin. The mean \m=+-\ s.e.m. concentrations (pg/follicle) in Groups AC, BC, CC and DC were 26\m=.\5\m=+-\3\m=.\04,93\m=.\1 \ m=+-\ 4\m=.\6, 138 \ m=+-\ 16\m=.\4and 285\m=.\6 \ m=+-\ 54\m=.\1 respectively. Therefore relaxin production was stimulated by PMSG (P < 0\m=.\05), with hCG treatment in vivo leading to a further significant increase (P < 0\m=.\05). In-vitro treatment with gonadotrophins had no effect in Groups A, C and D, but in Group-B gilts LH produced a significant (P < 0\m=.\05) rise in relaxin levels. These studies indicate that the theca is the principal source of relaxin in the porcine preovulatory follicle. The increased production before ovulation suggests that relaxin may be involved in follicular growth or rupture.
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