AJP - Regulatory, Integrative and Comparative Physiology, Vol 232, Issue 3 101-R109, Copyright © 1977 by American Physiological Society
Coupling of signals to brown fat: alpha- and beta-adrenergic responses in intact rats
K. E. Flaim, B. A. Horwitz and J. M. Horowitz
The present study examines the effects of alpha- and beta-adrenergic
antagonists (phentolamine and propranolol, respectively) and agonists
(phenylephrine, isoproterenol) on the neurally induced temperature changes
and membrane potentials of interscapular brown adipocytes. These studies,
performed in vivo with anesthetized rats, indicate that both alpha- and
beta-adrenergic components are associated with the biphasic temperature
changes observed following sympathetic activation of the tissue.
Specifically, the initial transient temperature decrease seen after brown
fat stimulation appeared to reflect vasoconstriction mediated primarily via
alpha-receptors, while the subsequent rise in tissue temperature was
associated primarily (though perhaps not entirely) with beta-adrenergic
pathways. In contrast, the redistribution of ions across the membrane of
the brown adipocyte, a phenomenon manifested as a membrane depolarization,
was elicited by phenylephrine (an alpha-agonist) as well as by
isoproterenol (a beta-agonist), with the magnitude of the
isoproterenol-induced depolarization being comparable to that of the
phenylephrine-induced effect.
