Pharmacologic Profile of the Dihydropyrimidine Calcium Channel Blockers SQ 32,547 and SQ 32,946

SQ 32,926 and SQ 32,547, two dihydropyrimidine calcium channel blockers, were characterized as potent inhibitors of depolarization-induced contractions of isolated smooth muscle preparations. In rat aorta, the IC50 values were 5.5 nM for SQ 32,547 and 8.1 nM for SQ 32,926, values which compare favorably with that of 2.9 nM for nifedipine. The dihydropyrimidines were also tested in a model of stable angina: pacing-induced ischemia in dogs. Both SQ 32,547 and SQ 32,926 reduced the ST-segment elevation observed in vehicle-treated animals. No significant changes in hemodynamic status were detected, suggesting that a reduction in cardiac work secondary to afterload reduction was probably not a major contributor to the protective effects. Neither was increased coronary blood flow important for the antiischemic outcome because no significant effects of the dihydropyrimidines were observed on ischemic regional blood flow. SQ 32,547 was also studied in globally ischemic, isolated rat hearts. In this model, SQ 32,547 was protective because it significantly reduced contracture formation and lactate dehydrogenase (LDH) release. Washing out the effect of SQ 32,547 in isolated hearts and smooth muscles was difficult, presumably due to its lipophilicity. In the smooth muscle preparations, the effects of both nifedipine and SQ 32,926 were much more easily washed out. As with other calcium channel blockers, increasing the antiischemic effects of SQ 32,547 was associated with a higher cost in terms of cardiac function. In summary, the two novel dihydropyrimidines, SQ 32,547 and SQ 32,926 showed antiischemic properties in animal models.