Dissociation of hypertension and enhanced clonidine-induced antinociception in spontaneously hypertensive rats.

Abstract

In the present study, we evaluated the relationship between hypertension and the antinociceptive effect of clonidine in genetically hypertensive rats. Intraperitoneal (i.p.) administration of clonidine (0.69 mg/kg) produced hypoalgesia without lowering blood pressure in conscious spontaneously hypertensive (SH), spontaneously hypertensive-stroke prone (SH-SP) and Wistar-Kyoto (WKY) rats. The antinociceptive effect of clonidine, measured by the hot plate method, was greater in the hypertensive rats (SH-SP) than in their normotensive controls (WKY). The enhancement of clonidine-induced antinociception in these genetically hypertensive rats was not altered after acute lowering of blood pressure with guanethidine. Furthermore, the development of this hyper-antinociceptive effect of clonidine was earlier than that of hypertension in SH rats. In conclusion, our data suggest that the enhanced antinociceptive effect of clonidine in hypertensive animals is not directly related to blood pressure.