Cardiovascular actions of the dihydropyridine calcium antagonist nimodipine in the dog.

When injected i.v. into anaesthetized, open-chest dogs, isopropyl (2-methoxyethyl)-1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3, 5-pyridinedicarboxylate (nimodipine, Bay e 9736) (0.3-10 micrograms/kg) produced an increase in coronary sinus outflow and decreases in mean arterial blood pressure, coronary resistance, arterio-venous oxygen difference and heart rate in a dose-dependent manner, but virtually no change in myocardial oxygen consumption. At 3 micrograms/kg i.v. of the drug coronary resistance fell nearly to half the pre-drug value, coronary sinus outflow nearly doubled and heart rate decreased by about 10 beats/min. Myocardial oxygen consumption was slightly reduced at 30 micrograms/kg i.v. and atrioventricular (AV) conduction time was slightly increased at 10 and 30 micrograms/kg i.v. of the drugs. When the coronary vascular and cardiac effects of nimodipine were assessed in isolated, blood-perfused dog heart preparations, i.e., sinoatrial node, AV node and papillary muscle preparations, by intra-arterial administration, the following was revealed. In nearly twice the dose doubling coronary arterial blood flow, nimodipine produced a 15% decrease in sinus rate and a 15% increase in AV conduction time. However, in reducing the force of contraction of the papillary muscle by half the pre-drug value was needed nearly 17 times the dose of nimodipine doubling coronary arterial blood flow. Suppression of AV conduction by large doses of nimodipine was evident only when it was injected into the artery supplying the AV node but not into the artery supplying the His-Purkinje-ventricular system.(ABSTRACT TRUNCATED AT 250 WORDS)