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Ovarian Response to Pregnant Mare Serum Gonadotropin and Porcine Pituitary Extract in Gilts Actively Immunized against Gonadotropin Releasing Hormone^1,2,

North Carolina State University³, Raleigh 27695-7621

Abstract

Two experiments were conducted to determine the effect of exogenous gonadotropins on follicular development in gilts actively immunized against gonadotropin releasing hormone (GnRH). Four gilts, which had become acyclic after immunization against GnRH, and four control gilts were given 1,000 IU pregnant mare serum gonadotropin (PMSG), while four additional control gilts were given saline. Control animals were prepuberal crossbred gilts averaging 100 kg body weight. Control gilts given saline had ovaries containing antral follicles (4 to 6 mm in diameter). Control gilts given PMSG exhibited estrus and their ovaries contained corpora hemorrhagica and corpora lutea. PMSG failed to stimulate follicular growth in gilts immunized against GnRH, and ovaries contained regressed corpora albicantia and small antral follicles (<1 mm in diameter). Concentrations of luteinizing hormone (LH) and estradiol-17ß (E₂) were non-detectable in gilts immunized against GnRH and given PMSG. In the second experiment, five gilts actively immunized against GnRH were given increasing doses of PMSG every third day until unilateral ovariectomy on d 50. PMSG failed to stimulate follicular growth, and concentrations of follicle stimulating hormone (FSH), E₂ and LH were not detectable. Six weeks later, gilts were given a booster immunization and then were given 112 µg LH and 15 µg FSH intravenously every 6 h for 9 d. The remaining ovary was removed on d 10. Although LH and FSH concentrations were elevated, administration of gonadotropins did not stimulate follicular growth or increase E₂ concentrations. These results indicate that neither PMSG or exogenous LH and FSH can induce E₂ synthesis or sustain follicular development in gilts actively immunized against GnRH.

¹ Paper no. 10919 of the Journal Series of the North Carolina Agric. Res. Serv., Raleigh, NC 27695-7601. The use of trade names in this publication does not imply endorsement by the North Carolina Agric. Res. Serv. of the products named, nor criticism of similar ones not mentioned.

² Acknowledgement is made to Dr. R. R. Kraeling for giving the pituitary powder; Dr. G. D. Niswender for supplying antisera to luteinizing hormone, Dr. L. E. Reichert, Jr. for providing purified porcine LH (LER 786-3); Dr. D. J. Bolt, USDA Hormone Program, for donating porcine FSH antisera and purified porcine FSH; Vickie Hedgpeth and Robin Scott for technical assistance; and Pearl Wilkins for secretarial assistance.

³ Dept. of Anim. Sci.