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

Abstract

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 17β‐hydroxy‐androgens and total estrogens were measured for all samples and testosterone, dihydrotestosterone, 3α‐andostanediol, 3β‐androstanediol, 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 17β‐hydroxy‐androgens were normal (∼1.4 ng/ml) 12 days after hemicastration, the concentration of total 17β‐hydroxy‐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 5α‐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/min/stallion in 12 days. Concentrations of total estrogens in testicular vein blood were similar for the first and second testes (27, 400 pg/ml) 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) apparently decreased by 50%. Although anesthesia plus hemicastration may have altered blood flow to the remaining testis, a change in blood flow could not account for the concurrent increase in testosterone and decrease in estrogen clearance rates. Injection of 1500 IU of hCG markedly increased (P < 0.01) the concentration of total 17β‐hydroxy‐androgens in testicular vein blood 1 hour later, but the concentration of total estrogens was unaltered 1 or 2 hours after treatment. We concluded that the concentrations of total 17β‐hydroxy‐androgens and total estrogens in jugular blood bear little relationship to their concentrations a few minutes earlier in venous blood draining the testis.