Involvement of opioid receptors in nucleus tractus solitarii in modulating endotoxic hypotension in rats.

Opioid antagonists selective for the mu-receptor (naltrexone) and kappa-receptor (nalmefene), respectively, were unilaterally microinjected into the nucleus tractus solitarii (NTS) of the pentobarbital anaesthetized (50 mg/kg, i.p.) rat subjected to E. coli endotoxin (15 mg/kg, i.v.). Naltrexone (0.5 microgram) ameliorated or totally abolished the endotoxic hypotension and tachycardia, and nalmefene at a dose of 1/25 (0.02 microgram) that of naltrexone showed a similar effect. The results suggest that the kappa- and mu-opioid receptors in NTS are actively involved in mediating the hypotensive and tachycardiac effects induced by systemic endotoxin in rats.