Evidence for activation of the central nervous system-pituitary mechanism for gonadotropin secretion at the time of puberty in the male rat
Date
1986-07Author
Dorsa, Daniel M.
Southworth, Molly B.
Bremner, William J.
Matsumoto, Alvin M.
Karpas, Anthony E.
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Show full item recordAbstract
During sexual development in the male rat, serum testosterone (T) levels
increase markedly at 45-60 days of age. At the time of the pubertal rise
in T levels, activation of the hypothalamic-pituitary axis is difficult to
demonstrate, since there is little change in serum LH levels and a
decrease in serum FSH levels. We determined whether experimental
maintenance of stable pubertal T levels in these animals as they passed
through the normal age of puberty would allow demonstration of a major
increase in serum gonadotropin levels. At 14-15 days of age, male rats
were castrated and outfitted with either T-containing or empty Silastic
capsules. Another group of rats was left intact and outfitted with empty
capsules. At various times between 29 and 58 days of age, blood was drawn
for measurement of serum LH, FSH, and T levels. In the T-implanted
castrated rats, serum T levels were comparable to those in midpubertal
intact rats, without significant differences among age groups. In this
setting of stable T levels, serum LH and FSH were suppressed to levels at
or below those in pubertal intact rats until 51 days of age, when they
increased significantly into the untreated castrate range. In contrast,
untreated castrate animals demonstrated markedly reduced serum T and
elevated LH and FSH levels that did not change significantly throughout
the entire study. In intact rats, serum T levels were stable until 58 days
of age, when they increased over 2-fold; serum LH levels did not change
significantly with age, and serum FSH levels decreased significantly by 54
days of age. A separate group of rats was castrated and outfitted with
T-containing Silastic capsules at 21 days of age. In these animals, there
were significant increases in hypothalamic LHRH, norepinephrine (NE), and
dopamine levels and NE turnover rate at 56 compared to 36 days of age. We
conclude that stable pubertal levels of T are able to suppress
gonadotropin levels in castrated rats until the normal age of puberty, at
which time LH and FSH levels increase markedly. This decrease in
sensitivity of the hypothalamic-pituitary axis to T negative feedback at
puberty is accompanied by increases in hypothalamic LHRH, NE, and dopamine
levels and NE turnover rate. These results provide direct evidence for
activation of the central nervous system-pituitary mechanism regulating
gonadotropin secretion at puberty in the male rat.(ABSTRACT TRUNCATED AT
400 WORDS)