AJP - Regulatory, Integrative and Comparative Physiology, Vol 246, Issue 5 747-R752, Copyright © 1984 by American Physiological Society
Isoproterenol-induced blood flow in rats acclimated to room temperature and cold
S. J. Wickler, B. A. Horwitz, S. F. Flaim and K. F. LaNoue
Blood flow was measured with labeled microspheres in cold (6 degrees C)-
and room-temperature-acclimated rats at rest and during infusion of the
beta-agonist, isoproterenol. Isoproterenol elicited decreased mass-specific
blood flows (ml . g-1 . min-1) to liver (55% of control), kidney (48%), and
white fat (64%) in room-temperature-acclimated (RT) rats. Blood flow was
similarly decreased in liver (51%), kidney (37%), and white fat (70%) in
cold-acclimated (CA) rats. In contrast, isoproterenol increased blood flows
to brown fat and cardiac and skeletal muscles. The blood flows to cardiac
muscle during isoproterenol infusion were comparable in both RT (12.7 ml .
g-1 . min-1) and CA (11.7 ml . g-1 . min-1) animals, representing increases
of 2.9- and 2.6-fold above control values, respectively. Blood flow to
skeletal muscle was also similarly elevated in RT and CA animals,
representing increases 5.9 and 5.6 times those of their respective control
values. In contrast, although isoproterenol greatly stimulated (ca. 8-fold)
blood flow to brown fat (interscapular plus cervical depots) in RT animals,
it had a greater effect on these two depots in the CA rats (18-fold
increase). These data emphasize the importance of brown fat as a major
effector of nonshivering thermogenesis as well as the importance of
beta-adrenergic receptors in mediating the metabolic response of
nonshivering thermogenesis.
