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1 Animal Reproduction Laboratory,
Department of Physiology and Biophysics,
Colorado State University, Fort Collins,
Colorado; and the Section of Clinical
Reproduction, School of Veterinary
Medicine, University of Pennsylvania,
Kennett Square, Pennsylvania
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 17
-hydroxy-androgens and total estrogens were
measured for all samples and testosterone,
dihydrotestosterone, 3
-andostanediol, 3
-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 17
-hydroxy-androgens
were normal (
1.4 ng/ml) 12 days after
hemicastration, the concentration of total 17
-hydroxy-androgens in testicular vein blood was
sixfold greater (P < 0.01) than it had been at
hemicastration (368 vs 62 ng/ml). The ratio of
testosterone to 5
-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 l/min/
stallion to
6.2 l/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/ml, respectively). Clearance rate
of estrogens (
23.3 l/min 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 17
-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 17
-hydroxy-androgens
and total estrogens in jugular blood bear little
relationship to their concentrations a few minutes earlier in venous blood draining the testis.
Key words: stallion, androgens, estrogens, testicular vein, hemicastration, hCG-treatment
Submitted on May 20, 1980
Revised on October 20, 1980
Accepted on November 10, 1980
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