Role of LH pulse amplitude in controlling rat ovarian oestradiol-17β secretion in vitro

Ovaries from di-oestrous rats were removed and placed in perifusion culture: 4-6 ovaries were cultured for 3 h with (1) no gonadotrophin; (2) tonic FSH (200 ng/ml); (3) tonic LH (30 ng/ml); (4) tonic FSH and tonic LH; (5) tonic FSH and hourly pulses of 40 ng LH/ml; or (6) tonic FSH and hourly pulses of 50 ng LH/ml. The total amount of LH administered was 3060 ng LH, regardless of mode of delivery. Perifusate was collected every 10 min and assayed for oestradiol-17 beta by RIA. The total amount of oestradiol-17 beta secreted was not altered by any treatment except when LH was administered in hourly pulses with an amplitude of 50 ng/ml; the total amount of oestradiol-17 beta secreted in 3 h was increased by 300% (P less than 0.05). Without gonadotrophic stimulation, oestradiol-17 beta was secreted at a constant rate (4.48 +/- 0.21 pg/mg 10 min-1). Tonic gonadotrophin stimulation did not alter this pattern. However, pulses of 50 ng LH/ml but not 40 ng LH/ml resulted in periodic increases in oestradiol-17 beta secretory rates. Thus, oestradiol-17 beta secretion is stimulated by LH pulses with the degree of stimulation dependent, in part, on the amplitude and/or the rate of change of the LH pulse.