AJP - Endocrinology and Metabolism, Vol 243, Issue 3 217-E224, Copyright © 1982 by American Physiological Society
Abnormal brown adipose composition and beta-adrenoceptor binding in obese Zucker rats
B. E. Levin, K. Comai, R. A. O'Brien and A. C. Sullivan
The composition, morphology, beta-adrenergic receptor binding, and in vitro
lipolysis were examined in lean and obese, 5- to 6-mo-old male Zucker rat
interscapular brown adipose tissue (IBAT). IBAT pads from obese rats were
heavier (283%), had more lipid (700%), and more (75%)( and larger (83%)
adipocytes than those from lean rats. Also, IBAT from obese rats had no
multiloculated cells, and 50% of their IBAT adipocytes were the size of
white fat cells. High affinity binding for (-)-[3H]dihydroalprenolol (KD,
15-18 nM), as well as the estimated KD values for binding and the 1/2 Vmax
values for adrenergic agonist-induced lipolysis were similar in isolated
IBAT cells from lean and obese rats. However, adipocytes from IBAT in obese
rats had 75% fewer high affinity beta-adrenergic binding sites per cell
(Bmax) compared to those in lean rats. These findings are most compatible
with the infiltration of IBAT by white adipocytes. Such infiltration would
be expected to reduce the overall thermogenic capacity of IBAT in obese
Zucker rats and thereby contribute to the maintenance of their obesity.
