Effects of exogenous acidic fibroblast growth factor (aFGF), which is increased in the brain by food intake, on the plasma levels of catecholamines and on sympathetic efferent outflow were examined in anesthetized rats. A guide cannula was inserted into the cerebral third ventricle, and a vascular indwelling catheter was inserted into the right atrium from the jugular vein. Plasma epinephrine (Epi) and norepinephrine (NE) increased markedly in a dose-dependent manner for up to 120 min after intracerebroventricular or intravenous administration of aFGF (6-667 fmol/rat). Concomitant increases occurred in the efferent activity in the sympathetic nerves supplying the adrenal, spleen, and interscapular brown adipose tissue after the above administrations of aFGF. Both intravenous and intracerebroventricular administration of 10 ng basic FGF (bFGF) also increased sympathetic adrenal efferent activity and plasma Epi and NE concentrations. However, the increases induced by 10 ng bFGF were smaller than those induced by 10 ng aFGF. Bilateral splanchnicotomy completely prevented the increases in Epi induced by intracerebroventricular or intravenous aFGF but had less effect on the increases in NE. Pretreatment with an antibody against corticotropin-releasing factor (CRF), given via the intracerebroventricular route, significantly attenuated the increases in Epi and NE evoked by intracerebroventricular or intravenous administration of aFGF. Hepatic vagotomy also greatly reduced the increases in both catecholamines and the increases in sympathetic efferent firing rates evoked by intravenous administration of aFGF. These findings indicate that 1) aFGF administered intracerebroventricularly activates adrenomedullary secretion and sympathetic outflow via CRF release and 2) aFGF injected intravenously also induces sympathoadrenomedullary activation via centrally released CRF. The idea is discussed that sympathetic activation induced either by endogenous aFGF after feeding or by exogenously administered aFGF may play roles both in energy expenditure after overeating and in the modulation of immune functions.