The effect of almitrine bismesylate on the steady-state responses of arterial chemoreceptors to CO 2 and O 2 in the cat

Abstract

The interaction between almitrine bismesylate, a pharmacological stimulant of peripheral chemo-receptors, and varying levels of oxygen (P O 2 50–600 Torr) and carbon dioxide (P CO 2 10–65 Torr)_on steady state carotid chemoreceptor discharge was investigated in pentobarbitone-anaesthetized cats. Almitrine was given as constant intravenous (50 μg/kg per min for 4 min) and intracarotid infusions (4–16 μg/kg per min) at different levels of alveolar P O 2 ad P CO 2 . Almitrine always excited discharge. The intracarotid infusions at the lower infusion rate (4–8 μg/kg per min) and the i.v. infusions increased the slope of the isoxic response to CO 2. This effect could be reversed by raising P O 2 to high levels. Higher infusion rates of almitrine (16 μg/kg per min) displaced the CO 2 response curve upwards but did not increase its slope above that obtained in control conditions at end-tidal P O 2 of 50 Torr. However, as these higher infusion rates caused levels of discharge greater than those achieved during control conditions, their effects on control CO 2 sensitivity could not be ascertained. Our results suggest that almitrine excites carotid body chemoreceptors by a mechanism similar to that of hypoxia and not like that of carbon dioxide.