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Cardiovascular responses to verapamil and nifedipine in hypoventilated and hyperventilated rats

1 The influence of hypoventilation or hyperventilation on blood pressure and pulse rate responses to verapamil and nifedipine was studied in chloralose‐anaesthetized rats. 2 Artificial ventilation with room air at a fixed volume of 10 ml kg−1 successfully induced combinations of hypoxaemia, hypercarbia and acidosis at a ventilator rate of 37 strokes min−1 and of hyperoxaemia, hypocarbia and alkalosis at 160 strokes min−1. 3 Hypoventilation caused significant decreases in both the blood pressure and pulse rate, whereas hyperventilation produced significant increases in these parameters. 4 In the controls, intravenous injections of graded doses of either verapamil or nifedipine caused dose‐dependent decreases in mean blood pressure. The effects on pulse rate were not marked. 5 The hypotensive effects of verapamil were significantly more intense in hyperventilated rats, whereas those of nifedipine were significantly less pronounced in hypoventilated animals. The hypoventilated rats exhibited a significant dose‐dependent decrease in pulse rate in response to verapamil administration. 6 It is concluded that cardiovascular responses to verapamil, nifedipine and probably other calcium antagonists are altered in the presence of blood gas abnormalities.