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Regression of Induced Corpora Lutea by Human Chorionic Gonadotropin in Prepuberal Gilts¹

University of Georgia, Athens 30602 and US Department of Agriculture, Athens, GA 30613

Abstract

The effect of daily injections of human chorionic gonadotropin (HCG) on luteal maintenance in hysterectomized prepuberal gilts induced to ovulate and in hysterectomized mature gilts was studied. Twenty-four prepuberal gilts, 120 to 130 d of age, were induced to ovulate with 1,000 IU pregnant mare serum gonadotropin followed 72 h later with 500 IU HCG. Nine of the 24 prepuberal gilts (bred controls) were artificially inseminated on d 0 (d 0 = d after HCG). Mature gilts that had displayed one or more estrous cycles of 17 to 22 d were used (d 0 = onset of estrus). All gilts, except the bred controls, were totally hysterectomized on d 6 to 9 and their corpora lutea (CL) marked with charcoal. From d 10 through 29, eight prepuberal and 10 mature hysterectomized gilts received daily injections of 500 IU HCG in saline while seven prepuberal and eight mature hysterectomized gilts received daily injections of saline vehicle. Jugular blood samples were quantitated by radioimmunoassay for estrogen and 13,14-dihydro-15-keto prostaglandin F₂ (PGFM), a metabolite of prostaglandin F₂. One bred control gilt was pregnant on d 30, indicating that the prepuberal gilts used in the experiment were prepuberal. All mature gilts and six of seven prepuberal gilts that received saline had maintained CL to d 30. Eight of 10 mature gilts that received HCG had maintained CL to d 30, while only two of eight (P<.05) prepuberal gilts that received HCG maintained CL to d 30. All gilts receiving HCG had numerous follicles and accessory luteal structures. Serum estrogen concentrations in the HCG-treated mature gilts increased by d 12 and remained elevated. Serum estorgen concentrations in the HCG-treated prepuberal gilts increased by d 11, remained elevated through d 23 and returned to control concentrations by d 24. Serum PGFM concentrations did not differ among treatments. These results indicate that daily HCG administration caused regression of induced CL of prepuberal gilts but not of spontaneous CL of mature gilts.

¹ This research was supported by State and Hatch funds allocated to the Georgia Agr. Exp. Sta. and by USDA funds. The authors thank Dr. Terry E. Riser, Dept. of Anim. and Dairy Sci., Univ. of Georgia for his advice in conducting this research, Dr. Kenneth Kirton, The Upjohn Co., Kalamazoo, MI, for providing PGFM antiserum, Dr. Dennis N. Marple, Auburn Univ., Auburn, AL for providing estrogen antiserum, and Mary A. Hart, C. Richard Barb, Doris M. Powell and Bennett Johnson for excellent technical assistance.

² Dept. of Anim. and Dairy Sci., Univ. of Georgia, Athens 30602.

³ Anim. Physiol. Res. Unit, USDA, ARS, Richard B. Russell Agr. Res. Center, Athens, GA 30613.

⁴ Present address: Laboratory of Reproductive Physiology, School of Veterinary Medicine, Univ. of Pennsylvania, Philadelphia.