Steroid and pituitary hormone concentrations in the fluid of preovulatory bovine follicles relative to the peak of LH in the peripheral blood

Abstract

Summary. Preovulatory bovine follices (n = 73) were collected at different times after the onset of oestrus until shortly before ovulation, which occurred at 24 \m=+-\1 \ m=. \ 4h after the peak concentration of LH in the peripheral blood. Non-atretic antral follicles (n = 9) of 15\p=n-\19mm were also collected from cows during the luteal phase of the oestrous cycle. Follicular fluid concentrations of dehydroepiandrosterone, androstenedione and oestrone, and of LH, FSH and prolactin were compared in 2-h periods relative to the LH plasma peak. Before the LH surge the concentrations of the steroids were much higher than in non-atretic luteal-phase follicles of similar size. From 0 to 6 h after the LH peak the steroid concentrations decreased sharply to remain low until ovulation; only that of androstenedione increased again after 14 h to remain constant. The ratio between the concentrations of androstenedione and dehydroepiandrosterone remained constant until 14 h after the LH peak; at 14 h it increased about 4-fold and remained high until ovulation. The ratio between the oestrone and androstenedione concentration increased gradually to a 10-fold higher value until at 14 h an abrupt decrease was observed. These changes indicate that after the LH peak androgen production is directly inhibited and, at a slower rate, the aromatizing activity. Androstenedione appeared to be the major aromatase substrate.Before the plasma LH peak the follicular fluid concentration of FSH was higher than in luteal-phase follicles; the concentrations of LH and prolactin were not different from those in luteal-phase follicles. About 4 h after the LH plasma peak the LH concentration in follicular fluid reached a maximum, which was one seventh of that in peripheral blood; it remained elevated until 20 h. The FSH concentration was higher after the LH plasma peak than before; just before ovulation it was still 2-fold higher. The concentration of prolactin fluctuated throughout the preovulatory development from the onset of oestrus until ovulation. It is suggested that oestradiol biosynthesis in bovine preovulatory follicles is terminated by an inhibitory action of the preovulatory LH peak on androgen production.

Changes in pulsatile secretion patterns of LH, FSH, progesterone, androstenedione and oestradiol in cows after superovulation with PMSG

“…Therefore, the decrease in the androstenedione blood concentration during the follicular phase in treated as well as in control heifers can be related to increased oestradiol production by individual preovulatory follicles. This is supported by the higher concentrations of oestradiol, exceeding those of androstenedione, in follicular fluid of preovulatory follicles collected shortly before the LH surge (Dieleman et al, 1983b;Fortune & Hansel, 1985;Bevers et al, 1988b). Our data with regard to androstenedione are in agreement with studies of Schenken & Hodgen (1983) showing that hyperstimulation of follicular growth in monkeys by exogenous FSH had no effect on the peripheral blood concentrations of androstenedione.…”

“…The tip of the catheter was located in the vena cava near the bifurcation with the vena ovarica. Correct placing was assessed according to Walters et al (1984) (Dieleman et al, 1983b).…”

“…Plasma concentrations of FSH were estimated as described by Cheng (1978) and validated in our laboratory (Dieleman et al, 1983b). Plasma concentrations of LH and PMSG were estimated by previously validated RIA methods (Dieleman et al, 1983b;.…”

“…Plasma concentrations of LH and PMSG were estimated by previously validated RIA methods (Dieleman et al, 1983b;. The intra-and interassay coefficients of variation for the FSH, LH and PMSG RIA were <9 and <13% respectively.…”

FSH influences follicle viability, oestradiol biosynthesis and ovulation rate in Romney ewes

“…Also, the exogenous ovine FSH regimen was effective when administered for 24 h but not when administered for only 6 h. These findings suggest that during the 6 h treatment regimen the dose of ovine FSH may have been too low and/or that the granulosa cells were not exposed to the additional FSH for a sufficient period of time. The latter is a possibility because of the time required for proteins to traverse to the granulosa cells from the peripheral circulation (Cran, Moor & Hay, 1976 Dobson, Gibb, Kieboom & Thurley, 1981;Dieleman, Bevers, Poortman & van Toi, 1983).…”