We have examined whether or not the release of catecholamines into the blood circulation of rabbits during fever is mediated by prostaglandins. The plasma levels of catecholamines (epinephrine and norepinephrine) were measured in 2 ml of blood withdrawn from the marginal ear vein. At an ambient temperature of 21 +/- 1 degree C, intravenous injection of either lipopolysaccharide (LPS, 4 micrograms/kg) or human recombinant interleukin-1 beta (rIL-1 beta, 1 microgram/kg) produced a biphasic fever accompanied by an increase in the plasma level of catecholamines. Pretreatment with intravenous indomethacin (1 mg/kg) markedly suppressed the increase in catecholamines induced by LPS and rIL-1 beta. In contrast, although intracerebroventricular injection of rIL-1 beta (20 ng) produced fever, it did not produce a significant change in plasma catecholamine levels. Similarly, intrahypothalamic injection of prostaglandin E2 (200, 800 ng) induced fever, but did not cause a significant change in catecholamine concentrations. These results suggest that IL-1 acts via prostaglandins on the peripheral tissues to release catecholamines into the circulation.