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Abstract
Coruzzi P, Musiari L, Mossini GL, Ceriati R, Novarini A. Water immersion and salt-sensitivity in essential hypertension. Scand J Clin Lab Invest 1993; 53: 593-599.
It has been demonstrated that an exaggerated natriuretic response to central hypervolaemia is not necessarily associated with hypertension; many hypertensive subjects manifest either an appropriate or a blunted natriuresis in response to ECFV expansion attained by head-out water immersion. In this study, we tested the hypothesis that an underlying condition of salt-sensitivity may explain the heterogeneity of the natriuretic response of essential hypertension.
Both salt-sensitivity tests and 2h water-immersion studies were randomly performed in 18 untreated essential hypertensives under a selected and controlled diet. Salt-sensitivity was denned as a significant drop in mean arterial pressure of 10% or greater, calculated as the difference between the average of the 25 readings under the high and the low salt period.
Water immersion did result in a significant natriuretic and calciuretic response in the whole hypertensive group (n = 18, p < 0.001 and p < 0.05, respectively), while the examination of the individual excretion disclosed either exaggerated and appropriate or blunted urinary response. When the hypertensive group was classified in relation to salt-sensitivity, the greater fall in mean arterial pressure during low salt diet (salt-sensitivity) was associated with the more pronounced natriuretic response during water immersion (r = –0.66, p < 0.003). An identical correlation (r = -0.58, p < 0.01) was also found between changes in mean arterial pressure (low salt diet) and urinary calcium excretion (water immersion) in the same hypertensives. The water immersion-induced suppression of plasma aldosterone and the increase in plasma atrial natriuretic peptide did result from comparable magnitude in the salt-sensitive and in salt-resistant subjects.
Our data indicate that central hypervolaemia by water immersion is a reliable, alternative test of salt-sensitivity. Furthermore, it may be also suggested that not only renal sodium output but also urinary calcium excretion represent a truthful predictor of salt-sensitivity in essential hypertension.
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