Prepontine knife cut-induced hyperthermia in the rat. Effect of chemical sympathectomy and surgical denervation of brown adipose tissue.

Abstract

The effect of brown adipose tissue (BAT) denervation on the prepontine knife cut-induced hyperthermia was studied. The knife cut has earlier been shown to induce a steady state hyperthermia of 3 to 4 degrees C, as a result of marked activation of the BAT. Before the lesion, the interscapular BAT (IBAT) temperature was lower than the colonic temperature, but the temperature gradient reversed a few minutes after the lesion and the fractional blood flow increased 12-fold. Bilateral sectioning of the 5 nerves supplying IBAT did not modify either the magnitude or the kinetics of the IBAT hyperthermic response. The IBAT fractional blood flow, which was 15 times higher in denervated than in intact tissue before the lesion, scarcely increased following the lesion despite the sharp increase in the tissue's metabolic activity. Chemical sympathectomy with 6-hydroxydopamine suppressed the hyperthermic response. Propranolol or hexamethonium injected i.v. during the steady state hyperthermia resulted in a rapid drop in IBAT temperature and in a reversal of the gradient between IBAT and colonic temperature both in denervated and in intact IBAT. Injection of desipramine, an inhibitor of noradrenaline reuptake, resulted in itself in an increase of temperature in both intact and denervated tissue, which is circumstantial evidence for the presence of a functional residual innervation in the latter.(ABSTRACT TRUNCATED AT 250 WORDS)