Sodium-neural interactions in the development of spontaneous hypertension

The influence of alterations in sodium intake on blood pressure and indices of peripheral sympathetic activity was studied during the development of hypertension in the SHR. Male SHRs were given a diet containing either low (0.05%), normal (0.29%) or high (3.4%) sodium content beginning at 7 weeks of age. Systolic blood pressure was measured weekly by the tail cuff method in conscious animals. Three weeks after initiation of the diets 24 hour urines were collected for analysis of catecholamines. Plasma catecholamines were measured and the blood pressure response to ganglionic blockade (hexamethonium bromide, 30 mgm/kg) determined. High sodium resulted in a marked increase in the severity of hypertension that was associated with an increase in plasma and urinary norepinephrine concentration and an exaggerated depressor response to ganglionic blockade. In addition, a highly significant positive correlation was seen between plasma norepinephrine concentration and systolic blood pressure. The results are compatible with the hypothesis that the increase in blood pressure in the SHR maintained on a high sodium intake is in part due to an increase in peripheral sympathetic activity.