Involvement of spinal alpha adrenoceptors in mediation of the hypotensive action of guanabenz in rats.

The effects of intrathecal, intracisternal and intravenous injections of yohimbine (10 micrograms) on hypotensive and bradycardic responses to the alpha agonist guanabenz (10 micrograms/kg, i.v.) were studied in anesthetized rats. The depressor response to guanabenz was inhibited by intrathecal pretreatment with yohimbine, while this pretreatment did not affect the bradycardic response to guanabenz. Intracisternal pretreatment with yohimbine inhibited both cardiovascular responses to guanabenz, whereas intravenous pretreatment with yohimbine affected neither. Guanabenz (1 microgram) decreased blood pressure when injected intrathecally but did not affect it when injected intravenously. These results suggest that in rats spinal alpha adrenoceptors are involved in mediation of the hypotensive action of the alpha agonist guanabenz injected systemically.