Expression of angiotensin I-converting enzymes and bradykinin B2 receptors in mouse inner medullary-collecting duct cells.

We described in mouse inner medullary-collecting duct cells (mIMCD-3) the somatic and the N-domain ACE synthesis and its interaction with the kallikrein-kinin system co-localized in the same cells. We purified two ACE forms from culture medium, M1 (130 kDa) and M2 (N-domain, 60 kDa), and cellular lysate, C1 (130 kDa) and C2 (N-domain, 60 kDa). Captopril and enalaprilat inhibited the purified enzymes. The immunofluorescence studies indicated that ACE is present in the membrane, cytoplasm and in the cell nucleus. Kinin B1 and B2 receptors were detected by immunofluorescence and showed to be activated by BK and DesR9 BK, increasing the acidification rate which was enhanced in the presence of enalaprilat. The presence of secreted and intracellular ACE in mIMCD-3 confirmed the hypothesis previously proposed by our group for a new site of ACE secretion in the collecting duct.

The urinary activity of angiotensin-converting enzyme in preterm, full-term newborns, and children.

The urinary activity of the angiotensin-converting enzyme (U(ACE)) is not yet completely documented in human neonates. We measured the U(ACE) in 36 premature neonates on the 1st day and in the 1st, 2nd, 3rd, and 4th weeks of life, in 22 full-term neonates between the 1st and 2nd days, and in 30 nursing and preschool children between 1 month and 6 years of age. The urinary excretion of sodium (U(Na)/U(Cr)) and the potassium/sodium index (U(K)/U(Na)) were analyzed in the neonates. U(ACE) was greater in premature than in full-term neonates and greater in both than in older children (p<0.001). In the premature neonates, U(ACE) peaked at the 2nd week, the U(Na)/U(Cr) index decreased, and the U(K)/U(Na) index increased between the 1st day and the 2nd week (p<0.001). The U(Na)/U(Cr) index on the 1st day and in the 1st and 2nd weeks was greater in premature than in full-term neonates (p<0.001). There was no significant correlation between the U(ACE) and the U(Na)/U(Cr) index. In conclusion, the U(ACE) profile was shown to be age dependent and related to the postnatal renal development. The increase in U(ACE) activity may reflect the high activity of the neonatal intrarenal renin-angiotensin system (RAS).