Relationship Between the Preovulatory Luteinizing Hormone (LH) Surge and Androstenedione Synthesis of Preantral Follicles in the Cyclic Hamster: Detection by In Vitro Responses to LH 1

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Abstract
Preantral follicles of cyclic hamsters were isolated on proestrus, estrus and diestrus I, incubated for 3 h in 1 ml TC-199 containing 1 .mu.g ovine luteinizing hormone (LH) (NIH-S22), and the concentrations of progesterone (P), androstenedione (A) and estradiol (E2) determined by radioimmunoassay. At 0900-1000 h on proestrus (pre-LH surge) preantral follicles produced 2.4 .+-. 0.3 ng A/follicle per 3 h, < 100 pg E2/follicle and < 250 pg P/follicle. At the peak of the LH surge (1500-1600 h) preantral follicles produced 1.8 .+-. 0.2 ng P and 1.9 .+-. 0.1 A and < 100 pg E2/follicle. After the LH surge (1900-2000 h proestrus and 0900-1000 h estrus) preantral follicles were unable to produce A and E2 but produced 4.0 .+-. 1.0 and 5.0 .+-. 1.1 ng P/follicle; respectively. By 1500-1600 h estrus, the follicles produced 8.1 .+-. 3.1 ng P/follicle, but synthesized A (1.6 .+-. 0.2 ng/follicle) and E2 (362 .+-. 98 pg/follicle). On diestrus I (0900-1000 h), the large preantral-early antral follicles produced 1.9 .+-. 0.3 ng A, 2.4 .+-. 0.4 ng E2 and 0.7 .+-. 0.2 ng P/follicle. There was a shift in steroidogenesis by preantral follicles from A to P coincident with the LH surge; then, a shift from P to A to E2 after the LH surge. The LH/FSH surges were blocked by administration of 6.5 mg phenobarbital (PB)/100 g body wt at 1300 h proestrus. On Day 1 of delay (0900-1000 h) these follicles produced large quantities of A (2.2 .+-. 0.2 ng/follicle) and small amounts of E2 (273 .+-. 27 pg/follicle) but not P (< 250 pg/follicle). PB treatment with LH or LH/FSH induced the secretion of P; but not FSH + PB. LH + PB and/or FSH + PB induced A/E2 secretion by the follicles. Incubation of granulosa cells and theca at 0900 h and 1500 h estrus (when A production reappeared) indicated that theca was the major site of P and A synthesis in the preantral follicles. The LH surge enhances P production and inhibits A production in theca of preantral follicles and possibly regulates the onset of A/E2 synthesis during follicular development.

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