AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 5 963-R970, Copyright © 1986 by American Physiological Society
Decreased testosterone levels do not mediate short-photoperiod-induced brown fat changes
K. S. Kott, B. J. Moore and B. A. Horwitz
Previous studies showed that short photoperiod increased brown fat (BAT)
mass and reduced gonadal size and gonadal hormone secretion in hamsters.
The present study investigated the possibility that the effects on BAT were
dependent on reduced levels of gonadal hormones. BAT from male Syrian
hamsters exposed to short photoperiod for 10 wk was significantly greater
in mass, protein content, and total maximal citrate synthase and
beta-hydroxyacyl-CoA dehydrogenase activities than was BAT from
long-photoperiod hamsters, These differences between short- and
long-photoperiod exposure were observed in hamsters housed at 21 as well as
at 8 degrees C. Short photoperiod also increased the total recovered
mitochondrial GDP binding, a finding consistent with increased BAT
thermogenic capacity. These short-photoperiod effects were neither mimicked
by castration of long-photoperiod hamsters nor prevented by high levels of
testosterone administered to short-photoperiod animals. Castration did
attenuate the effects of short photoperiod on BAT growth if, after surgery
and prior to short-photoperiod exposure, the animals were housed at a long
photoperiod for 2-3 wk. In contrast, in hamsters immediately placed at
short photoperiod after surgery, castration did not inhibit
short-photoperiod effects. The present three experiments demonstrate that,
in addition to increasing BAT mass, short photoperiod elevates the
thermogenic capacity of BAT, and this elevation does not require the
absence or a much reduced testosterone level.
