Calcium antagonists have become widely used as antihypertensive treatment in diabetic patients, although data concerning a possible influence on glucose tolerance, insulin secretion, and platelet aggregation during long-term, placebo-controlled studies are lacking. Therefore, the effects of isradipine, a new calcium antagonist, on glucose tolerance and insulin secretion during a 75-g oral glucose tolerance test (OGTT) and on ADP- and collagen-induced maximum first-wave platelet aggregation (Tmax%) were studied in 11 type II diabetic patients with borderline hypertension. After a 2-week washout period, patients were treated with placebo or isradipine for 8 weeks in a double-blind, crossover study. Systolic blood pressure was lowered significantly after isradipine therapy compared to placebo (127 ± 3 vs. 139 ± 6 mm Hg; p < 0.05). Fasting blood glucose (153 ± 14 vs. 157 ± 16 mg/dl; NS), glucose levels, and basal (17 ± 4 vs. 17 ± 2 mU/ml; NS) and stimulated insulin during the OGTT remained unchanged after either treatment. Platelet aggregation after stimulation with different concentrations of ADP and collagen showed no significant differences. These data indicate that calcium antagonists have no adverse effects on glucose tolerance, insulin secretion, and platelet aggregation in type II diabetes mellitus, and are therefore useful in the treatment of hypertension in diabetic patients.
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