Is salt sensitivity in essential hypertension affected by ageing

: To investigate the question of whether the salt sensitivity of blood pressure in human essential hypertension is affected by ageing, the salt-sensitivity index was determined in 54 hospitalized patients with essential hypertension, aged 26-67 years (mean +/- s.d. 46.9 +/- 9.5 years) as well as plasma inhibition of Na+,K+-ATPase (sodium-pump inhibitor), erythrocyte sodium and potassium concentrations and fractional excretion of lithium. The salt-sensitivity index was calculated as the percentage change in mean blood pressure when the dietary sodium content was increased from 34 mmol/day (low sodium) to 340 mmol/day (high sodium) for 8 days each. Despite wide range of ages, age showed no correlation with the salt-sensitivity index, the sodium-pump inhibitor, the erythrocyte Na+:K+ ratio or fractional excretion of lithium. Furthermore, the distribution of the salt-sensitivity index did not differ between older (greater than or equal to 45 years old) and younger (less than 45 years old) age groups. In contrast, the distribution of this index was correlated positively with the change in sodium pump inhibition induced by a sodium load (r = 0.415, P less than 0.05) and negatively with the fractional excretion of lithium (r = -0.725, P less than 0.01). The erythrocyte Na+:K+ ratio tended to be higher in patients with a salt-sensitivity index of 10% than in those with an index of less than 5%.(ABSTRACT TRUNCATED AT 250 WORDS)