Ultrastructural changes in myocardium of hypertensive rats treated with nifedipine

Spontaneously hypertensive rats (SHR) with high systolic pressure received calcium antagonist nifedipine in medium therapeutic doses for 2 weeks. Electron microscopy of the myocardium revealed considerable changes in the sarcoplasmic reticulum manifested in dramatic dilation of tubules, destruction of membranes, and appearance of amorphous matter of medium electron density in tubules in animals treated with nifedipine. Since sarcoplasmic reticulum plays an important role in calcium-dependent excitation-contraction coupling, the observed structural changes can underlie the negative inotropic effect of long-term nifedipine therapy.