Function of Ovine Corpora Lutea after Administration of Luteinizing Hormone-Releasing Hormone

Abstract

Ewes were treated with an agonistic analog of luteinizing hormone-releasing hormone (LH-RH) during the luteal phase (d 10) of the estrous cycle. Function of natural and hormonally-induced corpora lutea (CL) was evaluated by measurements of progesterone in sera or luteal tissue. Synthesis and secretion of progesterone by natural CL were not chronically altered by LH-RH. Likewise, there was no in vitro effect of LH-RH on luteal function. When natural CL were surgically removed, newly formed CL functioned at a defective level. Hysterectomy shortly after ovulation did not significantly influence such luteal activity. Induction of ovulation by LH-RH during the follicular phase (d 16) in uterus-intact ewes was followed by normal profiles of luteal secretion of progesterone; serum concentrations of progesterone in animals that were hysterectomized increased in association with development of the CL, but then plateaued at a subnormal level. There were no differences in patterns of secretion of luteinizing hormone in response to LH-RH due to stage of the estrous cycle. Follicles stimulated to ovulate during the luteal phase contained low numbers of steroidogenically-deficient granulosal-lutein cells. These results indicate that: ovine CL are not sensitive to exogenous LH-RH; luteal dysfunction is a consequence of ovulation during the luteal phase, and the etiology of this abnormality appears to be linked with the developmental status of the ovulatory follicle; and CL that are formed from ovulation of a matured follicle begin to develop normally, but then function at a defective rate in the absence of the uterus.