No abstract

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.

No abstract

No abstract

This study was undertaken to examine the possibility that the prolonged anovulatory period frequently experienced by the post-partum cow is due to a disruption of function at the ovarian level promoted by the high, suckling-induced, blood prolactin concentrations. Fifteen cows, less than 35 days post partum, were allocated to three groups (1, 3 and 5) and given no hormonal treatment, prostaglandin plus pregnant mare serum gonadotrophin (PMSG) treatment or injected with 2-bromo-ex-ergocryptine to reduce circulating prolactin levels. Ten synchronized cyclic cows were allocated to two groups (2 and 4) and given prostaglandin or prostaglandin plus PMSG treatment. All cows were ovariectomized 1 or 2 days after treatment and Graafian follicles less than 9 mm in diameter were selected after dissection from the ovaries. The follicles were cultured for 18 h with or without prolactin (1 fLgfml) and steroid accumulation in the culture medium estimated. The follicles were then separated into theca and granulosa which were incubated for 40 min with LH (1 fLgfml) or FSH (5 fLgfml). Cyclic AMP concentrations were estimated as an indication of tissue responsiveness to gonadotrophins.The secretion of oestradiol-17 p, progesterone, testosterone or androstenedione during 18 h culture did not differ between follicles isolated from post-partum or cyclic cows. The presence of prolactin in the culture medium had no overall effect on steroid secretion although some specific effects within each group were noticed. Incubation with LH increased cyclic AMP levels in the theca but the granulosa did not respond. Likewise FSH increased cyclic AMP levels in granulosa preparations but not in theca. There were no differences in response between post-partum and cyclic cows, but exposure of the follicles to prolactin in vitro did significantly reduce the LH-induced increase in cyclic AMP levels in isolated theca.We have concluded that endogenous prolactin may modify but does not inhibit the resumption of ovarian function following parturition in the beef cow.