Impaired mechanical response to calcium of diabetic rat hearts: reversal by nifedipine treatment.

Streptozotocin-induced diabetic and age-matched control rats were treated with 0.03% nifedipine-containing chow for 6 weeks, and mechanical response to Ca2+ was studied using isolated working hearts. At 14 weeks of age, 7 weeks after a streptozotocin injection, diabetic rats had a lower body weight and heart weight than controls, and an increase in heart weight-to-body weight ratio. Nifedipine treatment did not alter these parameters of controls, but decreased the heart weight and heart weight-to-body weight ratio of diabetic rats without affecting the body weight. In diabetic rats, systolic blood pressure was decreased compared to controls (124 +/- 5 vs. 137 +/- 6 mm Hg, p < 0.01), and reduced more by nifedipine treatment (111 +/- 4 mm Hg, p < 0.01). In control rats, LV developed pressure, LV +/- dP/dt, and cardiac work were unchanged regardless of the increment in preload at 1.25, 1.88, and 2.50 mM Ca2+. However, the responses of diabetic rats were decreased with an increment in preload at 2.5 mM Ca2+. Nifedipine treatment produced a partial recovery of all four parameters at 2.5 mM Ca2+ in diabetic rats. The myocardial Ca2+ content and sarcolemmal lipid peroxidation were similar in hearts from control and diabetic rats at all Ca2+ concentrations and nifedipine treatment did not affect these values. Results suggest that chronic nifedipine treatment improve the contractility of diabetic rat hearts under high Ca2+ conditions.