AJP - Regulatory, Integrative and Comparative Physiology, Vol 245, Issue 3 357-R363, Copyright © 1983 by American Physiological Society
Increased beta-adrenergic receptors in brown fat of winter-acclimatized Alaskan voles
D. D. Feist
To assess a possible mechanism for the enhanced thermogenesis of
cold-acclimated and winter-acclimatized red-backed voles (Clethrionomys
rutilus), beta-adrenergic receptors of brown fat were characterized by
specific binding of (-)-[3H]-dihydroalprenolol [( 3H]DHA) to isolated brown
fat membranes from 23 degrees C-acclimated controls, cold-acclimated (5 wk
or 5 mo at 5 degrees C), wild summer, and winter-acclimatized voles.
Scatchard analysis to determine the equilibrium dissociation constant (Kd)
and the maximum number of binding sites (Bmax) for control brown fat
membranes gave a Kd of 4.45 nM [3H]DHA and Bmax of 249 fmol [3H]DHA bound
per milligram of protein. beta-Adrenergic agonists competed for specific
binding sites with an order of potency typical of the beta 1 subtype of
adrenergic receptors: (-)-isoproterenol greater than (-)-norepinephrine
greater than or equal to (-)-epinephrine. After cold acclimation for 5 wk
or 5 mo, the Kd and Bmax for adrenergic binding sites were similar to those
of controls. Brown fat mass was 1.5 times greater than that of controls
after 5 wk cold acclimation but similar to controls after 5 mo cold
acclimation. Winter voles had 1.7 times higher Bmax and 1.6 times more
brown fat than summer voles. Thus seasonal acclimatization to winter in
red-backed voles appears to involve an increase in beta-adrenergic
receptors in brown fat, but cold acclimation does not. The results suggest
quantitative and possibly qualitative differences in neural and hormonal
stimulation of brown fat between cold acclimation and winter
acclimatization in voles.
