Pyrogens Enhance β-Endorphin Release in Hypothalamus and Trigger Fever That Can Be Attenuated by Buprenorphine

Abstract

ABSTRACT: At first, we investigated whether both β-endorphin release level in the hypothalamus and body temperature can be altered after intracerebroventricular (i.c.v.) injection of either lipopolysaccharide (LPS), interleukin-1β (IL-1β), or prostaglandin E2 (PGE2) in rats. It was found that in the rat, i.c.v. administration of either LPS (0.5 μg in 10 μl), IL-1β (10 ng in 10 μl), or PGE2 (200 ng in 10 μl), in addition to producing fever, upregulated the immunoreactivity of β-endorphin in the preoptic anterior hypothalamus of rat brain. Secondarily, we assessed whether the fever induced by either LPS, IL-1β, or PGE2 can be altered by pretreatment with buprenorphine (an opioid receptor antagonist). The results revealed that i.c.v. administration of buprenorphine (1 – 10 μg in 10 μl) alone had an insignificant effect on the body temperature. However, the fever induced by i.c.v. injection of either LPS, IL-1β, or PGE2 was significantly attenuated by pretreatment with i.c.v. injection of buprenorphine 1 h before the pyrogen injection in rats. The results suggest that pyrogens enhance β-endorphin release in the hypothalamus and trigger fever which can be attenuated by buprenorphine, an opioid receptor antagonist.