Effects of blood gas/pH abnormalities on the cardiovascular actions of verapamil in rats.

1. The effects of hypoxaemia, hyperoxaemia, alkalosis, acidosis, hypocarbia with alkalosis or hypercarbia with acidosis on the blood pressure and pulse rate responses to verapamil were studied in chloralose-anaesthetized rats. 2. At a fixed stroke volume (10 mL/kg) and rate (80 strokes/min; except for the hypocarbic group at 160 strokes/min), hypoxaemia, hyperoxaemia, hypercarbia with acidosis, or hypocarbia with alkalosis was induced by artificial ventilation with gas mixtures containing 17% O2, 28% O2, 23% O2, with 5% CO2, or 17% O2, without CO2 respectively. Acidosis or alkalosis was produced by intravenous infusion of 1 mol/L HCl or 1 mol/L NaHCO3 respectively, in animals artificially ventilated with room air. 3. Changes in individual blood gas/pH parameters had no significant effect on blood pressure except for acidosis which caused a significant decrease. Effects on pulse rate were significant increases in the alkalosis and hypercarbia groups, decrease in the acidosis group, while in other conditions no significant changes were recorded. 4. In the controls, intravenous injections of verapamil 20-320 micrograms/kg caused dose-dependent increases in mean blood pressure, while effects on pulse rate were not marked. 5. The hypotensive responses to verapamil were significantly alleviated or enhanced in the presence of alkalosis or acidosis respectively. Verapamil also caused greater falls in pulse rate during acidosis. Effects of Po2 changes were not statistically significant. The influence of PCO2 changes remained unclear. 6. The present findings suggest that changes in blood pH may play a more important role than Po2 alterations in affecting the cardiovascular responses to verapamil in the presence of blood gas abnormalities.