Effect of ovariectomy and ovarian steroid replacement of patterns of plasma LH in the bovine

Includes bibliographical references (leaves 52-58)A study was designed to evaluate the pulsatile patterns of plasma LH in five mature Jersey cows on day 3 of two consecutive estrous cycles, and at different time intervals following ovariectomy (4, 42 and >59 days postovariectomy). The patterns of LH from these bleeding periods were compared to determine if individual animals have inherent patterns of LH release from the pituitary when ovarian steroid feedback is minimal or absent. Additionally, these bleeding periods served as a time study of the effect of ovariectomy on the pulsatile patterns of LH. The animals were also used to study the feedback effects of progesterone on the patterns of plasma LH in short-term (11 days postovariectomy) and long-term (49 days post-ovariectomy) ovariectomized cows. A final study was performed to determine if a combination of estrogen with progesterone might enhance any feedback effect of progesterone. Ovarian steroids were administered with a Progesterone Releasing Intravaginal Device (PRID) which was inserted one week before the scheduled bleeding periods. Blood samples were collected from an indwelling jugular cannula at 10-min intervals during each of the bleeding periods. Concentrations of plasma LH and progesterone were quantitated by validated radioimmunoassays. No apparent inherent pattern of plasma LH was observed within individual cows when ovarian steroid feedback was minimal or absent, suggesting that the mechanism controlling pulsatile LH release is more complex than simple addition or removal of ovarian steroids. ..