AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 2 396-R404, Copyright © 1989 by American Physiological Society
Effects of norepinephrine and denervation on brown adipose tissue in Syrian hamsters
J. M. Hamilton, T. J. Bartness and G. N. Wade
Department of Psychology and Neuroscience, University of Massachusetts, Amherst 01003.
Daily injections of either 0.8 or 3.2 mg norepinephrine (NE)/kg for 2 wk
failed to stimulate brown adipose tissue (BAT) growth, GDP binding, or
cytochrome-c oxidase activity (COA) in Syrian hamsters (Mesocricetus
auratus). However, a single injection of 1.6 mg NE/kg produced a small
(23%) but significant acute increase in BAT GDP binding without affecting
COA. Thus there is some loss of sensitivity to NE with chronic treatment in
Syrian hamsters. Unilateral sympathectomy by surgical denervation of the
interscapular BAT (IBAT) resulted in decreased GDP binding and COA in the
denervated pad. Chronic NE treatment in hamsters with denervated IBAT only
partially reversed the denervation-induced decreases in GDP binding and
COA. It therefore appears that NE is not solely responsible for the
maintenance and stimulation of thermogenic activity and COA in Syrian
hamster BAT. Denervation of IBAT also resulted in elevated levels of
lipoprotein lipase (LPL) in this tissue, a surprising finding since brown
and white adipose tissue LPL activity were both stimulated by chronic NE
treatment. Therefore, although NE has a stimulatory effect on LPL activity,
the primary influence of the neural input to IBAT on this enzyme is
inhibitory. These data exemplify dramatic differences between rats and
hamsters in the mechanisms controlling BAT thermogenesis and white and
brown adipose tissue LPL activity.
