AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 6 1118-R1125, Copyright © 1986 by American Physiological Society
Insulin and metabolic efficiency in rats. II. Effects of NE and cold exposure
T. J. Bartness, C. J. Billington, A. S. Levine, J. E. Morley, N. E. Rowland and D. M. Brown
The role of insulin in metabolic efficiency (ME, i.e., efficiency of body
wt gain) was examined under conditions of maximal energy expenditure in
control and diabetic rats. Long-lasting insulin was administered using a
protocol that did not affect food intake and increased ME in both groups.
Half the animals were injected chronically with norepinephrine (NE). NE
alone in controls decreased body weight and ME and increased brown adipose
tissue (BAT) growth, thermogenic potential [cytochrome c oxidase activity
(COA)], and lipoprotein lipases (LPL) activity; however, in diabetics, body
weight, ME, and food intake all decreased and only BAT LPL activity and DNA
content increased. The combination of NE and insulin increased BAT protein
and COA in diabetics; in controls, all BAT measures were further increased
and ME was intermediate to that of either treatment alone. Cold exposure
decreased body weight and ME, increased food intake and qualitatively
produced similar increases in BAT growth, COA, and LPL activity in both
controls and diabetics. In diabetics, combined cold exposure and insulin
did not affect the increase in BAT growth or LPL activity resulting from
either treatment alone, but in controls this combination decreased BAT
growth and COA. It is concluded that, even under conditions of maximal
energy expenditure, both extremes of basal insulin status result in
decreased BAT growth and thermogenic potential, but have opposite effects
on ME.
