Free fatty acid mobilization in rats following intracerebroventricular norepinephrine

The possible involvement of central synaptic transmitters in lipomobilization was investigated by injecting norepinephrine or carbachol into the cerebrospinal fluid of conscious, unrestrained rats. Intracerebroventricular administration of minute amounts of norepinephrine (25-400 nmol in 5 microliters) induced a rapid increase in plasma free fatty acids (FFA) and glycerol. Small increases in blood sugar levels were induced only by the higher doses of norepinephrine. Plasma FFA response to the catecholamine was dose related in the range of 25-100 nmol of hormone. Previous intraventricular administration of propranolol, but not of phentolamine, completely blocked the lipomobilzing effect of intraventricular norepinephrine. In contrast to norepinephrine, carbachol (27 or 54 nmol) injected intraventricularly did not affect plasma FFA or glycerol levels, but markedly increased blood sugar levels. Increase of plasma FFA and glycerol by intraventricular norepinephrine and blockade of the response by propranolol suggest the involvement of a beta-adrenergic mechanism in the centrally mediated lipolysis activation. On the basis of these and previous results, it is hypothesized that central beta-adrenergic synapses relay impulses generated in receptors specifically involved in lipomobilization to the sympathetic fibers of adipose tissue.