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Effects of Intermittent Injections of LHRH on Specific Binding of ¹²⁵I-Labeled Gonadotropins to Granulosa and Theca, and Concentrations of Steroids in Serum and Ovarian Follicles During Postpartum Anovulation in Suckled Beef Cows^1,2,

Michigan State University^,7 East Lansing 48824 and U.S. Department of Agriculture^,6 Clay Center, NE 68933

Abstract

To examine ovarian follicular response to low-dose injections of luteinizing hormone-releasing hormone (LHRH), 32 anovulatory, suckled beef cows were allotted to one of four treatment groups and injected with either saline or 500 ng LHRH every 2 h for 48 or 96 h, starting 21.4 ± .4 d after parturition. Two hours after the last injection of LHRH, cows were ovariectomized and 10 to 15 ovarian follicles per pair of ovaries were removed and categorized by diameter as small (1.0 to 3.9 mm), medium (4.0 to 7.9 mm) or large (8.0 mm). Injections of LHRH did not affect (P>.10) steroid levels in small follicles or numbers of gonadotropin receptors in small and medium follicles. Concentrations of progesterone in fluid of medium follicles increased 1.5-fold (P<.05) after 96 h of LHRH, whereas concentrations of estradiol and androstenedione were unchanged. In fluid of large follicles, concentrations of progesterone were fourfold greater (P<.05) in LHRH-treated than in control cows at 48 h, but by 96 h progesterone was twofold greater (P<.05) in control than LHRH-treated cows. In large follicles, concentrations of estradiol were unchanged (P>.10) after 48 h of LHRH injections but after 96 h estradiol was twofold greater (P<.05) in LHRH-treated than control cows. Increased concentrations of estradiol in large follicles coincided with increased numbers of binding sites for human chorionic gonadotropin (hCG) but not follicle stimulating hormone (FSH) in granulosa and theca. At 96 h, a greater proportion (P<.05) of LHRH-treated than control cows had at least one large follicle with concentrations of estradiol greater than progesterone (estrogen-active). The high concentrations of estradiol in estrogen-active follicles in LHRH-treated cows were associated with greater binding capacity of FSH to granulosa cells than found in estrogen-inactive (progesterone > estradiol in fluid) follicles. We suggest that increased capacity of large follicles to produce initially progesterone and bind hCG, then produce subsequently greater amounts of estradiol and bind FSH may be important steps in initiating ovulation in anovulatory cows treated with low-dose injections of LHRH.

¹ Michigan Agr. Exp. Sta. Journal Article No. 11696.

² We thank Steven Lyth, Larry Chapin and Kathy Koudele for expert technical assistance; Dr. M. R. Sairam, Montreal, Quebec, Canada, for supplying highly purified ovine FSH; Dr. G. D. Niswender, Colorado State Univ., for supplying androstenedione antiserum; and the Natl. Pituitary Agency, NIAMDD, for supplying hCG (CR-119) and bovine LH.

³ Present address: M. S. Hershey Medical Center, Pennsylvania State Univ., Hershey, PA 17033.

⁴ Present address: Merck, Sharp and Dohme Res. Lab., Merck and Co., Inc., Rahway, NJ 07065.

⁵ To whom reprints request should be addressed.

⁶ Roman L. Hruska U. S. Meat Anim. Res. Center.

⁷ Dept. of Anim. Sci.

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