Renal dopamine and noradrenaline excretion during CNS-induced natriuresis in spontaneously hypertensive rats: influence of dietary sodium

Abnormalities in dopamine (DA) and noradrenaline (NA) activities and sodium handling may be involved in the pathogenesis of hypertension. The present study was designed to investigate whether any differences exist between nor motensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) in urinary excretion of DA, NA and sodium after 15 weeks on a low, medium or high sodium diet and during a subsequent elevation of the cerebroventric ular fluid sodium concentration (CNS-induced natriuresis). Seven features w ere noted: (1) Basal sodium and DA excretion after the diet regimen was cor related to the dietary sodium content in both strains, except that sodium a nd DA excretion in SHR showed no further increase after the high sodium die t over and above that after medium sodium diet. (2) For any given sodium di et, SHR excreted more DA and NA as compared with WKY. (3) Blood pressure in SHR, as opposed to that in WKY, was higher after medium and high sodium di et than after low sodium diet. (4) During CNS-induced natriuresis NA excret ion decreased or remained unchanged in WKY, but increased in SHR. (5) The D A/NA excretion ratio during CNS-induced natriuresis increased in WKY while decreased in SHR, which would not favour a natriuretic/vasodilatory respons e in the latter. (6) The ability of SHR to respond with CNS-induced natriur esis was attenuated after high sodium diet. (7) The magnitude of CNS-induce d natriuresis was in both strains correlated to the sodium diet; the higher the dietary sodium content, the greater the natriuretic response. In concl usion, the study shows some clear differences in the catecholamine and sodi um handling between WKY and SHR which may be involved in the pathogenesis o f hypertension in SHR. Furthermore, increased sodium in the diet sensitizes the brain and kidney to increase the ability to respond with natriuresis f or a given sodium stimulus.