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In Vitro Testosterone Secretion by Testicular Tissue from Young Bulls and the Effects of Chronic and Acute Exposure to Estradiol - 17β¹

University of Nebraska, Lincoln 68583 and and US Department of Agriculture, Clay Center, NE 68933

Abstract

The possibility that estradiol- 17β may directly influence testicular steroidogenesis in bulls was investigated in vitro. Testicular tissues were incubated for 4 h and regression coefficients (b, ng•ml^-1•h^-1) based on the increase in testosterone in the medium were used to describe testosterone secretion rates. In the first experiment, testicular tissues from control bulls and bulls chronically implanted with estradiol were incubated in the absence (basal conditions) or presence of 10 mlU/ml human chorionic gonadotropin (hCG). Under basal conditions, testosterone secretion rates were similar for tissues from control (b = 24.1 ± 6.0) and implanted (b = 34.7 ± 6.0) bulls. Testosterone secretion rates were increased approximately fourfold during incubation with hCG; tissues from implanted animals secreted testosterone at a higher rate (P<.05) than control tissues (b = 120.7 ± 6.0 vs 81.6 ± 6.0). In a second experiment, testicular tissues were obtained from control bulls and incubated both with and without hCG (10 mlU/ml) and with and without estradiol (concentrations ranging from 3.7 nM to 37 µM). In this experiment, basal secretion rate (b = 12.6 ± 3.6) was increased threefold during incubation with hCG (b = 37.8 ± 3.6). Estradiol failed to inhibit hCG-stimulated testosterone secretion when bovine testicular tissue was incubated with 0, 3.7 and 370 nM estradiol. In contrast, 37 µM estradiol suppressed (P<.05) testosterone secretion, perhaps reflecting a pharmacologic effect The results suggest that neither chronic nor acute exposure to estradiol direcdy affects testosterone secretion by the bovine testis. It is proposed, therefore, that the negative effects of chronic estradiol treatment on testicular development, previously reported in young bulls, are mediated by changes in luteinizing hormone secretion rather than by direct actions on the testes.

¹ Published as Paper No. 6625, Journal Series, Nebraska Agr. Exp. Sta. We are grateful to Cindy Rainbolt for technical assistance and Michael MacNeil for advice on analysis of data. We also thank Kathy Leising for typing the manuscript.

² Dept. of Anim. Sci., Univ. of Nebraska.

³ A University of Nebraska Research Fellow located at the Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, NE.

⁴ Roman L. Hruska U.S. Meat Animal Research Center, ARS, USDA.

⁵ Reprint requests: Dr. B. D. Schanbacher, Roman L. Hruska U.S. Meat Animal Research Center, P.O. Box 166, Clay Center, NE 68933.