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Biology of Reproduction, Vol 15, 141-146, Copyright © 1976 by Society for the Study of Reproduction

Pituitary-Testicular Responses in Rams to Prolonged Infusions of Luteinizing Hormone-Releasing Hormone (LHRH)

WILLIAM J. BREMNER 1, J. K. FINDLAY 1, I. A. CUMMING 1, B. HUDSON 1, , and D. M. de KRETSER 1

1 Medical Research Center, Prince Henry’s Hospital, Melbourne, 3004, Reproduction Research Section, University of Melbourne, and Department of Agriculture, S. S. Cameron Laboratory, Werribee, 3030, and Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, 3052


Luteinizing hormone releasing hormone (LHRH) was administered to adult rams as constant intravenous infusions lasting 4 to 6 h. Dosages of 0.05, 0.1, 0.5 and 1.0 ug/min were used. All studies were undertaken during the period of decreasing day length (January to June). Plasma luteinizing hormone (LH) values during administration of the two highest dosages revealed a biphasic pattern of increase during the first 2 h of the infusion, as has been found in similar studies in humans. LH values were maximal at approximately 2frac12 h of the infusions, then decreased in spite of continued LHRH administration, thereby demonstrating the development of pituitary refractoriness during prolonged LHRH administration. A similar refractory period has not been noted during analogous studies in men. Plasma follicle stimulating hormone (FSH) values generally increased gradually during LHRH infusions, with no evidence of a biphasic pattern. No FSH increase was noted in some studies, even at the highest LHRH dosage used.

Plasma testosterone (T) levels increased sharply 15-30 min after the initial rise in LH values. Maximal levels of T obtained were 3- to 5-fold greater than basal values and were considerably higher than those found during similar studies in men. These results suggest that T production from the ram testis is more sensitive to gonadotrophin stimulation than is that from the human testis. In spite of the prolonged elevations in gonadotrophins and the marked increases in plasma T levels, plasma estradiol levels were consistently close to or below assay sensitivity (15 pg/ml).

Note:
ACKNOWLEDGMENTS We appreciate the technical assistance of Mrs. Anne Davies, Ms. Ausma Dulmanis, Mr. Peter Langdon and Mr. R. W. Baxter, the typing of Mrs. Jill Volfsbergs and the illustrations of Ms. Anne Hayres. We are grateful to Dr. H. Papkoff for his gift of highly purified ovine FSH (49 x NIH-FSH-S1) and ovine LH (2 x NIH-LH-S1), to Hoechst Pharmaceuticals for their gift of synthetic LHRH, and to the National Institutes of Health for their gift of the gonadotrophin standards. This work was supported by grants from the National Health and Medical Research Council of Australia and the Australian Wool Research Trust Fund.

Submitted on January 14, 1976
Accepted on April 6, 1976






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Copyright © 1976 by the Society for the Study of Reproduction.