In vitro testosterone secretion by testicular tissue from young bulls and the effects of chronic and acute exposure to estradiol-17 beta.

The possibility that estradiol-17 beta may directly influence testicular steroidogenesis in bulls was investigated in vitro. Testicular tissues were incubated for 4 h and regression coefficients (b, ng X ml-1 X 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 mIU/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 less than .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 mIU/ml) and with and without estradiol (concentrations ranging from 3.7 nM to 37 microM). 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 microM estradiol suppressed (P less than .05) testosterone secretion, perhaps reflecting a pharmacologic effect. The results suggest that neither chronic nor acute exposure to estradiol directly affects testosterone secretion by the bovine testis.(ABSTRACT TRUNCATED AT 250 WORDS)