Inhibition by lithium of the nitrergic relaxation of rat anococcygeus muscle

Abstract

In the present study, we evaluated the effect of lithium on the nitric oxide (NO)-mediated nonadrenergic noncholinergic (NANC) relaxation of rat anococcygeus muscle. The isolated precontracted (phenylephrine, 7.5 μM) rat anococcygeus muscle were relaxed via electrical field stimulation (5 Hz) in the absence or presence of lithium (0.5, 1, and 5 mM) or in tissues excised from ex vivo lithium (600 mg/L in drinking water for 30 days)-treated animals. Effects of the NO synthase (NOS) inhibitor l-NAME (0.03 and 100 μM) or guanylyl cyclase inhibitor ODQ (1 μM) and NO precursor l-arginine (1 mM) on relaxations were investigated. Effect of either in vitro (1 and 5 mM) or ex vivo lithium treatment on relaxation to the NO donor sodium nitroprusside (SNP; 0.1–1000 μM) was also investigated on phenylephrine-contracted strips. The NANC relaxation was significantly reduced by in vitro (1 and 5 mM; up to P < 0.01) and ex vivo lithium treatment ( P < 0.001). l-NAME (100 μM and 1 mM) and ODQ (1 and 10 μM) significantly inhibited NANC relaxations in either control or lithium-treated strips. Combination of lithium (0.5 mM) with l-NAME (0.03 μM) significantly ( P < 0.001) reduced the NANC relaxation. Although 1 mM l-arginine had no effect on relaxations, it prevented their inhibition by both in vitro (1 and 5 mM) and ex vivo lithium of relaxations. SNP produced concentration-dependent relaxation in precontracted rat anococcygeus muscle which was not altered by lithium treatment. Reverse transcription polymerase chain reaction (RT-PCR) revealed a significant increase in the neuronal NOS expression in the anococcygeus muscle of ex vivo lithium-treated animals compared with controls. Our experiments suggested that both ex vivo and in vitro lithium administration attenuated the NO-mediated neurogenic relaxation of isolated rat anococcygeus muscle.