Steroid Production by the Bovine Testis and Steroid Transfer Across the Pampiniform Plexus1

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Abstract
Plasma concentrations of 8 steroids were measured in blood from the testicular vein, testicular artery and systemic circulation of standing conscious bulls. Testosterone (including .apprx. 5% dihydrotestosterone) concentration in testicular venous blood was 75-575 ng/ml. Concentration of other steroids in venous blood were correlated (r > 0.89) with those of testosterone. Steroid concentrations (ng/ml) in testicular venous blood averaged (N = 10-12): 5-androstenediol, 14.7; progesterone, 5.7; androstenedione, 6.4; testosterone plus dihydrotestosterone, 184; 3.alpha.-androstanediol, 7.0; 3.beta.-androstanediol, 10.4; and estradiol plus estrone, 0.020. Except for androstenedione, the concentration of each steroid was about 2-5.times. that in rete testis fluid. Based on data from 5 conscious bulls and 2 bulls anesthesized with halothane and given HCG [human chorionic gonadotropin], testosterone and estrogens were transferred from testicular venous to testicular arterial blood across the pampiniform plexus. Similar transfer of adrostenedione and progesterone was not detected. There was more (P < 0.01) testosterone in testicular arterial blood than in systemic blood (9.1 vs. 4.8 ng/ml; N = 35), although the mass of steroid transferred represented only 0.8% of that in testicular venous plasma. For both testosterone and estrogens, the percentage of steroid transferred across the pampiniform plexus was independent of venous steroid concentration. The transfer of estrogens could serve as a short feed-back loop to modulate Leydig cell function. Transfer of testosterone may provide the proximal epididymis with twice the concentration of androgen that is available in systemic blood.

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