Endocrinology, Vol 101, 1210-1215, Copyright © 1977 by Endocrine Society
The interaction of the photoperiod and testosterone in regulating serum gonadotropin levels in castrated male hamsters
FW Turek
Castrated adult male golden hamsters maintained on either a stimulatory (LD
14:10) or a nonstimulatory (LD 6:18 ) light cycle for 10 weeks following
surgery were implanted sc with empty or testosterone-filled Silastic
capsules of various lengths. Capsules which maintained circulating androgen
levels between 0.5 and 1.7 ng/ml reduced serum levels of LH and FSH in
castrated animals exposed to LD 6:18 but not in animals maintained on LD
14:10. When serum androgen levels were maintained at about 3 ng/ml, serum
gonadotropin levels were reduced 30-- 35-fold in nonphotostimulated
hamsters but only 2--3-fold in photostimulated animals. Maintenance of
serum androgen levels at 14--17 ng/ml induced a maximum decrease in serum
LH and FSH in animals exposed to either photoperiod. These results indicate
that exposure to short days for 10 weeks renders the
hypothalamic-hypophyseal axis of the castrate hamster extremely sensitive
to the negative feedback effect of testosterone. This alteration in steroid
feedback sensitivity may be one way in which the photoperiod acts to alter
neuroendocrine-gonadal activity in seasonally breeding animals.
