Prepontine knife cut-induced hyperthermia in the rat

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 induced a steady state hyperthermia of 3 to 4°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. These results indicate that vasomotor fibres run within intercostal nerves supplying IBAT and since severing of these nerves did not prevent the sympathetic stimulation of the tissue, it can be inferred that the residual innervation entering the IBAT along with the blood vessels is conveying stimulating signals originating in peripheral structures. The observation made by Moragas and Toran (1985) of a very active lipolysis in BAT from anencephalic infants are discussed in the context of these findings.