Coupling of signals to brown fat: alpha- and beta-adrenergic responses in intact rats

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.