Participation of sympathetic and vagal tones in the hypotensive and bradycardic effects of some 5-HT1-like receptor agonists in the rat.

In normotensive anaesthetized rats, 8-OH-DPAT, RU 24969 and 5-MeODMT, three 5-HT1-like receptor agonists, decreased blood pressure and heart rate. The decrease in blood pressure was suppressed by pithing or pretreatment with hexamethonium. Bilateral section of the vagus nerves, pretreatment with a beta-adrenoceptor blocking agent or with atropine, combination of bivagotomy plus beta-adrenoceptor blockade strongly reduced the bradycardia. These results are compatible with a centrally-mediated decrease in sympathetic tone and increase in vagal tone, as the cause of the hypotension and bradycardia induced by these 5-HT1-like receptor agonists in normotensive anaesthetized rats.