AJP - Endocrinology and Metabolism, Vol 247, Issue 1 94-100, Copyright © 1984 by American Physiological Society
Defective brown adipose oxygen consumption in obese Zucker rats
B. E. Levin, M. B. Finnegan, E. Marquet and A. C. Sullivan
The thermogenic capacity and morphologic characteristics of interscapular
brown adipose tissue (IBAT) were assessed in 3- to 4-mo-old male, lean and
obese Zucker rats. Pads from obese rats were threefold heavier and
contained similar numbers of cells but an average of 50% fewer multilocular
cells than pads from lean rats and 40% less mitochondrial protein per pad.
The maximal number of beta-adrenoreceptor binding sites, as assessed by
[125I]iodocyanopindolol binding to isolated brown adipocytes from obese
rats was 50% of that in lean rats on a per cell and per pad basis. Basal
and norepinephrine (NE)-stimulated in vitro oxygen consumption in isolated
brown adipocytes from lean rats correlated directly with the proportion of
mutilocular cells present. This correlation was not seen in cells from
obese rats that had a 50% decrease in their basal respiratory rates and
could not be further stimulated by excess NE or fatty acid. Electron
micrographs of IBAT from obese rats revealed distorted mitochondrial shapes
and cristae patterns and the presence of numerous inclusion bodies. Because
NE-stimulated lipolysis had previously been shown to be normal in the obese
Zucker rat, these data suggest that defective BAT thermogenesis in the
obese rat is due to an inability of mitochondria to utilize free fatty
acids for the production of enhanced oxygen consumption.
