• Am. J. Physiol. Regul. Integr. Comp. Physiol. · Feb 2002

    Antipyretic role of the NO-cGMP pathway in the anteroventral preoptic region of the rat brain.

    • Alexandre A Steiner, Jose Antunes-Rodrigues, Samuel M McCann, and Luiz G S Branco.
    • Departamento de Fisiologia, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, 14040 - 904 Ribeirão Preto, São Paulo, Brazil.
    • Am. J. Physiol. Regul. Integr. Comp. Physiol. 2002 Feb 1;282(2):R584-93.

    AbstractWe tested the hypothesis that nitric oxide (NO) acts in the anteroventral preoptic region (AVPO) modulating fever. To this end, body core temperature (T(c)) of rats was monitored by biotelemetry before and after pharmacological modulation of the NO pathway. Nitrite/nitrate and cGMP in the anteroventral third ventricular region (AV3V), where the AVPO is located, were also determined. Intra-AVPO microinjection of the NO synthase (NOS) inhibitor N(G)-monomethyl-L-arginine (L-NMMA, 12.5 microg) did not affect basal T(c), but it enhanced the early stage of lipopolysaccharide (LPS) fever, indicating that NO plays an antipyretic role in the AVPO. In agreement, intra-AVPO microinjection of the NO donor sodium nitroprusside (5 microg) reduced T(c). The antipyretic effect of NO seems to be mediated by cGMP because 1) NO has been shown to activate soluble guanylate cyclase, 2) intra-AVPO microinjection of 8-bromo-cGMP (8-BrcGMP) reduced T(c), and 3) the changes in AV3V levels of nitrite/nitrate and cGMP were similar in the course of fever. Additionally, we observed that nitrite/nitrate and cGMP levels decreased in the AV3V after, but not before, the onset of LPS fever, showing that the activity of the NO-cGMP pathway is reduced in the AV3V after intraperitoneal LPS, a mechanism that could contribute to the genesis and maintenance of fever. It was also observed that the efficacy of 8-BrcGMP in reducing T(c) in the AVPO is increased after LPS, emphasizing that the NO-cGMP pathway is antipyretic. This response could explain why intra-AVPO L-NMMA enhanced the early stage of LPS fever, even though the activity of the NO pathway before the onset of fever was unchanged. In summary, these data support an antipyretic role of the NO-cGMP pathway in the AVPO.

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