Effect of Alterations in Pulsatile Luteinizing Hormone Release on Ovarian Follicular Atresia and Steroid Secretion on Diestrus 1 in the Rat Estrous Cycle1

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Abstract
The importance of pulsatile luteinizing hormone (LH) release on diestrus 1 (D1; metestrus) in the rat estrous cycle to ovarian follicular development and estradiol (E2) secretion was investigated. Single injections of a LHRH antagonist given at -7.5 h prior to the onset of a 3 h blood sampling period on D1 reduced mean blood LH levels by decreasing LH pulse amplitude, while frequency was not altered. Sequential injections at -7.5 and -3.5 h completely eliminated pulsatile LH secretion. Neither treatment altered the total number of follicles/ovary > 150 .mu. in diameter, the number of follicles in any size group between 150 and 551 .mu., or plasma E2, progesterone or FSH levels. Both treatments with LHRH antagonist significantly increased the percentage of atretric follicles in the ovary. Apparently, pulsatile LH release is an important factor in determining the rate at which follicles undergo atresia on D1; reductions in LH pulse amplitude alone are sufficient to increase the rate of follicular atresia on D1; an absence of pulsatile LH release for a period of up to 10 h on D1 is not sufficient to produce a decline in ovarian E2 secretion, most likely because the atretic process was in its early stages and had not yet affected a sufficient number of E2-secreting granulosa cells to reduce the follicle''s capacity to secrete E2; and suppression or elimination of pulsatile LH release on D1 is not associated with diminished FSH secretion.