Abstract
Spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) were placed on sodium restricted diets (9 and 17 umol/g) or on a regular sodium diet (101 umol/g) at 2, 4, 7, or 10 weeks of age, and continued until 16 weeks of age. Severe sodium restriction (9 umol/g) initiated at 2 or 4 weeks of age prevented hypertension development in SHR and severely retarded growth. Hypertension development was attenuated when 9 umol/g was initiated at 7 weeks of age, and was not affected when started at 10 weeks of age. Mean arterial pressure (MAP) in WKY receiving 9 umol Na/g initiated at 2 and 4 weeks of age was below normal, but was not affected when this diet was given at 7 or 10 weeks of age. Less severe sodium restriction (17 umol Na/g) resulted in a reduction in hypertension development when initiated at 2, 4, and 7 weeks of age, but not at 10 weeks of age. MAP was normal in WKY receiving 17 umol Na/g at all ages of diet initiation. When the 9 or 17 umol Na/g diet were initiated at 2, 4, and 7 weeks of age, the response of blood pressure to hexamethonium administration was blunted in SHR relative to both WKY receiving the same diet, and to control SHR receiving 101 umol Na/g. We conclude that both WKY and SHR require a minimum amount of dietary sodium for normal growth and for the achievement of normal BP in WKY, and hypertension in SHR. This sodium requirement decreases with age. SHR and WKY exhibit similar sensitivities to sodium intake with respect to body weight, but the effects on BP are more pronounced in SHR. The BP lowering effects of dietary sodium restriction may be due to a blunting of the pressor effectiveness of the sympathetic nervous system.
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