Molecular forms of plasma and urinary adrenomedullin in normal, essential hypertension and chronic renal failure

Human adrenomedullin precursor is converted to glycine-extended adrenomedullin (AM-Gly), an intermediate inactive form of adrenomedullin. Subsequently, AM-Gly is converted to active form of mature adrenomedullin (AM-m). The aim of the present study was to investigate (i) whether sex or age influences plasma and urinary AM-m and AM-Gly levels in normal subjects; (ii) the daytime variability of plasma AM-m and AM-Gly levels in normal subjects; (iii) AM-m and AM-Gly levels and its ratio in plasma and urine in normal subjects, individuals with essential hypertension (HT), and chronic renal failure (CRF); and (iv) the ratio of AM-m and AM-total (T) in plasma of various veins and aorta.

We measured plasma levels and urinary excretions of AM-m, AM-Gly and AM-T (AM-m + AM-Gly) by recently developed immunoradiometric assay in normal subjects (n = 81), HT (n = 28) and CRF (n = 30). We also determined the molecular forms of plasma adrenomedullin taken from various sites during angiography in patients with suspected renovascular hypertension (n = 9).

There were no differences in plasma and urinary excretions of two molecular forms of adrenomedullin among sexes or ages in normal subjects. There was no daytime variation of plasma two molecular forms of adrenomedullin in normal subjects. Plasma AM-m, AM-Gly and AM-T levels were increased in patients with HT and CRF compared with normal subjects, whereas urinary AM-m, AM-Gly and AM-T excretions were decreased in patients with HT and CRF compared with normal subjects. Urinary AM-m: AM-T ratios were significantly higher than plasma AM-m: AM-T ratios. Plasma AM-m and AM-T levels taken from various veins were similar, and they were significantly higher than those of aorta, although there were no differences in plasma AM-Gly levels between aorta and veins.

These results suggest that in normal subjects, and individuals with HT and CRF: (i) plasma and urinary excretions of AM-m and AM-Gly are not affected by age or sex; (ii) AM-m in parallel with AM-Gly is increased; (iii) urine contains a higher percentage of active adrenomedullin than plasma; and (iv) plasma AM-m may be partly metabolized in the lung.