Characterization of Angiotensin-(1-7) in the Urine of Normal and Essential Hypertensive Subjects

A total of 31 healthy volunteers [39 ± 7 (SD) years] and 18 untreated essential hypertensive subjects [43 ± 9 years] collected urine for 24 h after a physical examination and laboratory tests. Radioimmunoassay measurements of angiotensin-(1-7) [Ang-(1-7)] in urine and plasma were done as described previously. Sitting systolic and diastolic blood pressures (± SD) averaged 118 ± 11/74 ± 7 mm Hg and 146 ± 16/96 ± 8 mm Hg in normal and essential hypertensive subjects, respectively (P< .001), whereas 24 h urinary volume was not different in normal and essential hypertensive subjects (P> .05). The concentration of Ang-(1-7) in the urine of normal subjects averaged 62.6 ± 22.6 pmol/L corresponding to a urinary excretion rate of 98.9 ± 44.7 pmol/24 h. Concurrent measurements of plasma Ang-(1-7) showed that the content of Ang-(1-7) in urine was 2.5-fold higher than that measured in the plasma. In contrast, untreated essential hypertensive subjects had lower concentrations and 24 h urinary excretion rates of Ang-(1-7) averaging 39.4 ± 18.0 pmol/L and 60.2 ± 14.6 pmol/24 h, respectively, (P< .001). Differences in the excretory rate of Ang-(1-7) between normal volunteers and essential hypertensive subjects were not modified by normalization of the data by urinary creatinine excretion rates. Urinary concentrations of Ang-(1-7) correlated inversely with systolic, diastolic and mean arterial pressures (r = −0.48, P< .001). Both urinary Ang-(1-7) [odds ratio of 0.92 (95% CI: 0.88–0.97)] and age were independent predictors of systolic blood pressure. These studies demonstrated the presence of Ang-(1-7) in urine and the existence of reduced levels of the heptapeptide in individuals with untreated essential hypertension. The relatively higher concentrations of Ang-(1-7) in urine compared to plasma agrees with data that showed that Ang-(1-7) may contribute to the regulation of blood pressure. The inverse association between Ang-(1-7) and arterial pressure provides a potential marker for the characterization of forms of essential hypertension associated with reduced production or activity of vasodilator hormones.