EVIDENCE THAT CHANGES IN LUTEINIZING-HORMONE SECRETION REGULATE THE GROWTH OF THE PREOVULATORY FOLLICLE IN THE EWE

The level of LH [luteinizing hormone] secretion preceding the preovulatory LH surge was studied as to whether it is an important determinant of follicular maturation and corpus luteum function in the ewe. Whether the pattern of LH delivery to the ovary (pulsatile vs. constant) is a critical factor in the maturation of a preovulatory follicle was examined. To accomplish this, progesterone-primed anestrous ewes were repeatedly injected i.v. with LH or LHRH, or given an i.v. infusion of LH, over a 72 h period. These animals, together with the appropriate controls, were exposed to a sexually active ram so that estrous activity could be recorded. All ewes were subjected to intensive blood sampling regimes so that the plasma levels of LH and progesterone could be determined and compared to those which occurred in the same breed of sheep during the estrous cycle. The plasma LH levels preceding the preovulatory LH surge are an important determinant of follicular maturation as judged by subsequent corpus luteum function. Follicular maturation can be achieved with widely differing patterns of LH delivery to the ovary during the preovulatory period; a strict pulsatile delivery of LH may not be an absolute requirement.