The influence of low Na diet on the sympathetic nervous system and the alpha-receptor of renal basolateral membrane in spontaneously hypertensive rat.

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In Wistar rats bred successively on a diet containing the minimum sodium required for normal growth, blood pressure was lower and sympathetic nervous function was suppressed compared to those on normal sodium diet. However, SHR bred on the same sodium depleted diet grew up to hypertensive. To clarify why dietary sodium restriction has no effect to prevent hypertension in SHR, we studied an influence of sodium depletion on alpha-adrnergic receptors which were concerned with reabsorption of sodium in the renal tubules.Wistar Kyoto rat (WKY) and SHR were fed with a diet containing low Na (0.05%) or normal Na (0.4%). One day after the measurements of blood pressure, body weight and 24 hour urinary Na output at the age of 6, 8, 20 weeks, the kidneys were removed and the basolateral membranes of renal proximal tubules were preparated using Percall. Assay of adrenergic receptors was accomplished through the use of [^3H]-prazosin, alpha-1 antagonist, and [^3H]-rauwolscine, alpha-2 antagonist.B … More ody growth and blood pressure in WKY on low Na diet were similar to those on normal Na diet. Maximum binding (Bmax) for alpha-1 receptors was not different between the normal-and low-Na group at any age. Dissociation constants (Kd) increased at 8 weeks of age with no difference between the both groups. Bmax and Kd for alpha-2 receptor was similar between two groups in WKY.There was no difference in body growth and blood pressure between the low- and normal-Na group in SHR. Blood pressure increased to a hypertensive level at the age of 8 weeks. Urinary sodium excretion for 24 hours was less in SHR on low-Na than the expected. There was no significant difference in both Bmax and Kd for alpha-1 receptor between the normal-and low-Na group in SHR at any age. Bmax for the alpha-2 receptor increased markedly at 8 weeks of age in SHR on low-Na, while it increased slightly but significantly with aging in SHR on normal-Na diet. Bmax at 8 weeks of age on low-Na was higher than that in SHR on normal-Na diet or WKY on low-Na. Kd for alpha-2 receptor was similar between the 2 groups at all age of the week. The results suggest that SHR has access to increase alpha-2 receptors in the renal tubules even under sodium restriction, which might accelerate Na reabsorption and produce hypertension. Less