DIETARY-SODIUM AND THE ANTIHYPERTENSIVE EFFECT OF NIFEDIPINE IN SPONTANEOUSLY HYPERTENSIVE RATS

To assess the interaction of dietary sodium and the antihypertensive response to a calcium antagonist, spontaneously hypertensive rats (SHR) were given a diet of regular or increased (120 v 342-mu-mol Na+/g food) sodium intake from 4 until 16 weeks of age. Nifedipine was added at 10 weeks of age. This level of sodium intake did not enhance the development of hypertension in SHR. In rats with the regular sodium intake, nifedipine caused only a minor decrease in blood pressure. In contrast, with increased sodium intake nifedipine caused a marked antihypertensive response, preventing the rise in blood pressure occurring between 10 and 16 weeks of age. This enhanced response was associated with a diminished blood pressure fall from ganglionic blockade. These results indicate that modest increases in sodium intake enhance the blood pressure response to a calcium antagonist possibly by potentiating its inhibitory effects on sympathetic activity.