The central action of the 5-HT₂ receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) on cardiac inotropy and vascular resistance in the anaesthetized cat

Abstract

1. Experiments were carried out to determine the effects of the application of the selective 5-HT₂ receptor agonist DOI intravenously (in the presence of the peripherally acting 5-HT₂ receptor antagonist, BW501C67, 1 mg kg⁻¹, i.v.) or to the `glycine sensitive area' of the ventral surface (30 μg each side) on the left ventricular inotropic (left ventricular dP/dt max) and vascularly isolated hindlimb responses in anaesthetized cats. For the ventral surface experiments, NMDA (10 μg each side) was applied to act as a positive control. In all experiments heart rate and mean arterial blood pressure were held constant to exclude any secondary effects caused by changes in these variables.

2. DOI (n=6) i.v or on the ventral surface had no effect on left ventricular dP/dt max but caused a significant increase in hindlimb perfusion pressure of 40±9 and 50±14 mmHg, respectively. Respiration was unaffected. NMDA (n=6), applied to the ventral surface, caused significant increases in both left ventricular dP/dt max and hindlimb perfusion pressure of 1950±349 mmHg s⁻¹ and 69±17 mmHg respectively, with no associated change in left ventricular end-diastolic pressure. The amplitude of respiratory movements increased.

3. It is concluded that activation of 5-HT₂ receptors at the level of the rostral ventrolateral medulla (RVLM) excites sympathetic premotor neurons and/or their antecedents controlling hindlimb vascular resistance but not those controlling the inotropic effects on the left ventricle.

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