Effects of Hemicastration or hCG-treatment on Steroids in Testicular Vein and Jugular Vein Blood of Stallions

The relationships among testicular vein and jugular vein concentrations of androgens and estrogens were studied in anesthetized stallions. Blood was sampled from a vein on the surface of the testis and simultaneously from an artery on the surface of the testis and from the jugular vein. Concentrations of total 173hydroxy-androgens and total estrogens were measured for all samples and testosterone, dihydrotestosterone, 3a-andostanediol, 33androstanediol, and 5-androstenediol were quantified In selected samples. Following halothane anesthesia and hemicastration of 19 stallions, the testosterone concentration in jugular blood dropped over 3 hours but returned to normal within two days. Although jugular levels of total 1 7-hydroxy-androgens were normal (-1.4 ng/ml) 12 days after hemicastration, the concentration of total 1 7f3hydroxy-androgens in testicular vein blood was sixfold greater (P < 0.01) than it had been at hemlcastratlon (368 vs 62 nglml). The ratio of testosterone to 5a-reduced-androgens was similar in testicular vein blood from the first and second testes. Apparently, the clearance rate for testosterone had changed from --2.4 I/minI stallion to -6.2 1/mm/stallion in 12 days. Concentrations of total estrogens in testicular vein blood were similar for the first and second testes (27,400 pg/mI) as compared with the values for jugular vein and testicular artery blood (63 and 293 pg/mI, respectively). Clearance rate of estrogens (-23.3 1/mm in Intact stallions) ap-