Influence of sodium intake on the reliability of active renin as a measureof the renin-angiotensin system in essential hypertension

Plasma renin activity (PRA) active renin (AR), prorenin, and angiotensinoge n were assessed in 486 hypertensive and 175 normotensive subjects with a so dium intake of 10 or 200 mEq/d during supine and upright posture and after infusion of angiotensin II. PRA and AR levels were compared in hypertensive subjects in each condition. With low sodium intake, particularly while upr ight, there was a significant correlation between PRA and AR. In upright su bjects with low sodium intake who had a PRA of 2.4 ng/mL per hour or less ( 1.85 nmol.L-1.h(-1) or less), the correlation was also strong. With high so dium intake, the correlation was weaker With intermediate sodium excretion, the correlation was intermediate. Prorenin was less predictive of PRA than was AR, and angiotensinogen had a marginal role. Using PRA during sodium r estriction while upright as the standard for determining renin status, the precision of AR for predicting renin status was excellent. AR may be used f or surrogate assessment of the renin-angiotensin system activity when the s ystem is activated.