However, when ewes were treated with an LHRH antagonist on Day 13, progesterone secretion declined rapidly with concurrent regression of the CL. Episodic release of LH pulses is required for CL development but is not required to maintain luteal function in cattle. When episodic release of LH was inhibited by treatment with an LHRH antagonist from Days 2 to 7 or 7 to 12 of the estrous cycle, there was diminished luteal function compared with that in untreated control females. Treatment with LHRH antagonist on Days 12-17 of the estrous cycle, however, did not affect luteal function as determined by concentrations of progesterone in blood plasma.
Episodic release of LH pulses before the preovulatory surge of gonadotropins may be important for inducing maturation of the dominant ovarian follicle. Women who were infertile due to luteal phase deficiency had a greater frequency of release of LH pulses during the early follicular phase in comparison to women with typical luteal function. There were, however, fewer LH pulses during the early follicular phase of the menstrual cycle in women with a subfunctional CL than in women with typical luteal function. Normal development and function of the CL, therefore, require a frequency of LH pulses in an optimal range, and deviations from this pattern of LH pulses can be detrimental for development of the structure and function of luteal tissue. There is little information about the role of episodic release of LH pulses during the follicular phase and the periovulatory stages of reproductive cycles on luteal development and function; therefore, the specific objective of the present study was to assess the role of episodic LH pulses before, during, and after the preovulatory surge of LH on development and function of the CL of cattle.