[Hemodynamic profile of 8-OH-DPAT and 5-HT1 agonists in the anesthetized dog]

In anaesthetized dogs, intravenous administration of 8-OH-DPAT (1-300 micrograms/kg i.v.) induced dose-dependent decrease in blood pressure (BP) and total peripheral resistance (TPR). Heart rate (HR) and cardiac output (CO) changed little. 5-Carboxamidotryptamine (5-CT) (0.3-3 micrograms/kg i.v.) dose-dependently decreased BP and TPR but increased HR, CO, myocardial contractility and pulmonary arterial pressure (PAP). 5-MeODMT and RU 24969 decreased BP only after the highest dose used (300 micrograms/kg i.v. and 1 mg/kg i.v. respectively) but significantly increased PAP at all doses used. These results indicated that in dogs as in other animal species, 8-OH-DPAT decreases BP by systemic vasodilatation without a reflex activation of the myocardium. This lack of a reflex tachycardia suggests a centrally-mediated effects of 8-OH-DPAT. In contrast to 8-OH-DPAT, the vasodilatation induced by 5-CT triggers a reflex tachycardia. The increase in PAP induced by 5-MeODMT, RU 24969 and--to a lesser extent--5-CT, may be due to a direct stimulation of 5-HT2 receptors. However, a 5-HT1 component could not be ruled out.