Heroin modulates the expression of inducible nitric oxide synthase

The use of heroin (diacetylmorphine) is associated with a high incidence of infectious disease, and the immunologic alterations responsible for heroin -induced changes in resistance to infection have not been well characterize d. The present study tests the hypothesis that expression of inducible nitr ic oxide synthase (iNOS) is modulated by the administration of heroin. The initial study using rats showed that heroin administration (0, 0.01, 0.1, o r 1.0 mg/kg s.c.) results in a pronounced reduction in lipopolysaccharide ( LPS)-induced expression of iNOS mRNA in spleen, lung, and liver tissue as m easured by RT-PCR, Heroin also produced a reduction in the level of plasma nitrite/nitrate, the more stable end-product of nitric oxide degradation. I n a subsequent study, administration of the opioid receptor antagonist, nal trexone (0.1 mg/kg) prior to the injection of heroin (1.0 mg/kg) blocked th e heroin-induced reduction of iNOS expression and plasma nitrite/nitrate le vels indicating that the effect is mediated via the opioid-receptor. This s tudy provides the first evidence that heroin induces an alteration of iNOS expression. and suggests that a reduction in nitric oxide production may be involved in the increased incidence of infectious diseases amongst heroin users. (C) 2000 Elsevier Science B.V. All rights reserved.