Systemic and Regional Haemodynamic Effects of 1–(2, 5–Dimethoxy-4–IODO-Phenyl)-2–Aminopropane (DOI) and α-Methyl-5–HT, in the Anaesthetised Rat

Abstract

The present experiment was performed to investigate the haemodynamic effects of 1–(2, 5–dimethoxy-4–iodophenyl)-2–aminopropane (DOI) and α-methyl-5–hydroxytryptamine (α-methyl-5–HT) in the anaesthetised normotensive rat. DOI (1–300 μg/kg i. v.) increased mean arterial pressure (MAP), total peripheral resistance (TPR) and decreased cardiac output (CO) and heart rate (HR). DOI increased all vascular resistances investigated (hindquarters, mesenteric and renal). Alpha-methyl-5–HT (10–300 μg/kg i. v.) dose-dependently increased MAP, TPR, all regional vascular resistances and decreased CO and HR. The bradycardia induced by α-methyl-5–HT was suppressed by bivagotomy. Both DOI and α-methyl-5–HT were more effective on renal vascular bed than hindquarters and mesenteric vascular beds. The effects of DOI and α-methyl-5–HT were antagonised by spiperone (10 or 100 μg/kg i. v.) and LY 53857 (10 μg/kg i. v.). Intracerebroventricular administration of DOI (100 μg/kg) increased MAP, TPR, regional vascular resistances and did not change HR and CO. Pretreatment with xylamidine (10 μg/kg i. v.), a selective peripheral 5–HT₂ receptor antagonist, blocked i. v. and i. c. v. effects of DOI.

Key Words:

• DOI
• α-methyl-5–HT
• haemodynamics
• 5–HT₂ receptors