Effect of the gonadotrophin surge at pro-oestrus on steroidogenesis and gonadotrophin binding of preantral follicles in the cyclic hamster.

The present study describes the acute changes in steroids and human chorionic gonadotrophin (hCG) and FSH binding of preantral follicles induced by the gonadotrophin surges on the day of pro-oestrus. Preantral follicles were isolated by microdissection before (09.00-10.00 h), during (15.00-16.00 h) and after (21.00-22.00 h) the LH surge on pro-oestrus. Follicles at each time-period were pooled and steroid concentrations and gonadotrophin receptors determined. Before the LH surge, concentrations of progesterone and androstenedione were 40.8 +/- 6.1 (S.E.M.) and 10.7 +/- 3.9 fmol/follicle respectively. At the peak of the LH surge, progesterone and androstenedione concentrations in preantral follicles increased to 848 +/- 186 and 129 +/- 33 fmol/follicle respectively. Immediately after the LH surge, progesterone increased to 1238 +/- 97 fmol/follicle whereas androstenedione declined to 13.3 +/- 2.1 fmol/follicle. Oestradiol was less than 6 fmol/follicle throughout these periods. Binding of hCG and FSH to preantral follicles increased after the surge (hCG, 56 +/- 2.6 c.p.m./follicle; FSH, 29.8 +/- 4.0 c.p.m./follicle) when compared with values obtained before the surge (hCG, 15.8 +/- 4.0 c.p.m./follicle; FSH, 14.1 +/- 1.9 c.p.m./follicle). Also, hCG binding increased significantly (P less than 0.05) from 09.00 to 21.00 h (56 +/- 2.6 c.p.m./follicle). In order to ascertain which follicular compartments were affected by the LH and FSH surges on pro-oestrus, granulosa cells and thecae from preantral follicles were isolated and steroid concentrations and LH and FSH binding measured.(ABSTRACT TRUNCATED AT 250 WORDS)