Central injections of noradrenaline and adrenaline differentially affect plasma free fatty acid and glucose in conscious pigeons (Columba livia)

Abstract

The possible involvement of central noradrenergic and/or adrenergic circuits in central mechanisms controlling free fatty acids and glucose levels was investigated in conscious pigeons. The effects of intracerebroventricular injections of noradrenaline (80 nmol) or adrenaline (80 nmol) on plasma free fatty acids and glucose concentrations were examined. The possible role of the autonomic nervous system, of sympathetic terminals and of pituitary hormone release in the metabolic responses induced by intracerebroventricular injections of adrenaline and noradrenaline was investigated by systemic pretreatment with a ganglionic blocker (hexamethonium, 1 mg/100 g), guanethidine (5 mg/100 g), and somatostatin (15 μg/100 g), respectively, 15 min before intracerebroventricular administration of adrenaline, noradrenaline or vehicle. Intracerebroventricular noradrenaline injections strongly increased plasma free fatty acid concentration but evoked no change in blood glucose levels, while adrenaline treatment increased glycemia without affecting free fatty acid levels. Hexamethonium did not block the increase in plasma free fatty acids induced by noradrenaline, while somatostatin pretreatment abolished noradrenaline-induced lipolysis during the experimental period. Adrenaline-induced hyperglycemia was blocked by systemic injections of somatostatin, hexamethonium and guanethidine. The present results suggest that: (1) adrenergic and noradrenergic mechanisms may participate in central control of blood glucose and free fatty acids, respectively, as observed in mammals, (2) noradrenaline-induced lipolysis may be mediated by pituitary mechanisms, and (3) postganglionic sympathetic fibers, possibly innervating the endocrine pancreas, may be involved in adrenaline-induced hyperglycemia.