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

Preovulatory bovine follices (n = 73) were collected at different times after the onset of oestrus until shortly before ovulation, which occurred at 24 +/- 1 X 4 h after the peak concentration of LH in the peripheral blood. Non-atretic antral follicles (n = 9) of 15-19 mm 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.(ABSTRACT TRUNCATED AT 250 WORDS)