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Abstract. At first, we investigated whether both b-endorphin release level in the hypothalamus and body temperature can be altered after intracerebroventricular (i.c.v.) injection of either lipopolysaccharide (LPS), interleukin-1b (IL-1b), or prostaglandin E 2 (PGE 2 ) in rats. It was found that in the rat, i.c.v. administration of either LPS (0.5 m g in 10 m l), IL-1b (10 ng in 10 ml), or PGE 2 (200 ng in 10 ml), in addition to producing fever, upregulated the immunoreactivity of b-endorphin in the preoptic anterior hypothalamus of rat brain. Secondarily, we assessed whether the fever induced by either LPS, IL-1b, or PGE 2 can be altered by pretreatment with buprenorphine (an opioid receptor antagonist). The results revealed that i.c.v. administration of buprenorphine (1 -10 m g in 10 ml) alone had an insignificant effect on the body temperature. However, the fever induced by i.c.v. injection of either LPS, IL-1b, or PGE 2 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 b-endorphin release in the hypothalamus and trigger fever which can be attenuated by buprenorphine, an opioid receptor antagonist.

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