Comparison of effects of some 5-HT1 agonists on blood pressure and heart rate of normotensive anaesthetized rats.

The present experiments served to compare the effects of the 3 5-HT1 agonists, 8-OH-DPAT, 5-MeODMT and TFMPP on the blood pressure and heart rate of normotensive anaesthetized rats. All the agonists induced, after i.v. injection, a decrease in blood pressure and heart rate. The hypotensive effects of 5-MeODMT and TFMPP were preceded by an increase, suppressed by both ketanserin and methysergide. The decrease in blood pressure induced by 5-MeODMT and 8-OH-DPAT was not antagonized by ketanserin, cocaine (and methysergide for 8-OH-DPAT) but was antagonized by methysergide (for 5-MeODMT) and spiroxatrine (for both). Bradycardia was not susceptible to ketanserin and cocaine (for 5-MeODMT) or to ketanserin and methysergide (for 8-OH-DPAT) but to methysergide and spiroxatrine (for 5-MeODMT) and cocaine and spiroxatrine (for 8-OH-DPAT). These results suggested that the hypotension and bradycardia induced by 5-MeODMT and 8-OH-DPAT are due to the stimulation of '5-HT1-like' receptors and probably to the 5-HT1A subtype; the 5-MeODMT-induced hypertension being ascribed to the stimulation of 5-HT2 receptors.