Modulatory action of FSH on LH-induced follicular growth in rats.

Three to four ovaries from rats on the day of di-oestrus I were placed in perifusion culture at 10:30 h and exposed to (1) no gonadotrophin (in-vitro controls); (2) tonic FSH (200 ng RP-1/ml); (3) tonic LH (30 ng RP-1/ml); (4) tonic FSH + tonic LH; or (5) tonic FSH plus hourly pulses of LH (amplitude = 50 ng/ml). The total amount of LH administered was 3060 ng RP-1 regardless of mode of delivery. After culture for 3 h, the ovaries were prepared for histological analysis. Compared to in-vitro controls, tonic LH stimulation increased the number of follicles with greater than 1.6 X 10(5) granulosa cells (P less than 0.05); it was estimated that each follicle in the larger size class increased by 5.5 +/- 2.7 X 10(4) cells. Tonic FSH or tonic FSH + tonic LH treatment did not promote growth into the 1.6 X 10(5) cell class. In the presence of tonic FSH, hourly LH pulses induced follicular growth similar to that observed after tonic LH treatment. The data demonstrate that LH promotes the growth of follicles in vitro. FSH modulates this stimulatory action of LH, allowing it to be expressed when LH is administered in hourly pulses.