Transendothelial transport of renin-angiotensin system components.

BACKGROUND: Vascular (interstitial) angiotensin (ANG) II production depends on circulating renin-angiotensin system (RAS) components. Mannose 6-phosphate (man-6-P) receptors and angiotensin II type 1 (AT(1)) receptors, via binding and internalization of (pro)renin and ANG II, respectively, could contribute to the transportation of these components across the endothelium. OBJECTIVE: To investigate the mechanism(s) contributing to transendothelial RAS component transport. METHODS: Human umbilical vein endothelial cells were cultured on transwell polycarbonate filters, and incubated with RAS components in the absence or presence of man-6-P, eprosartan or PD123319, to block man-6-P, AT(1) and angiotensin II type 2 (AT(2)) receptors, respectively. RESULTS: Apically applied (pro)renin and angiotensinogen slowly entered the basolateral compartment, in a similar manner as horseradish peroxidase, a molecule of comparable size that reaches the interstitium via diffusion only. Prorenin transport was unaffected by man-6-P. Apical ANG I and ANG II rapidly reached the basolateral fluid independent of AT(1) and AT(2) receptors. Basolateral ANG II during apical ANG I application was as high as apical ANG II, whereas during apical ANG II application it was lower. During basolateral ANG I application, ANG II generation occurred basolaterally only, in an angiotensin-converting enzyme (ACE)-dependent manner. CONCLUSIONS: Circulating (pro)renin, angiotensinogen, ANG I and ANG II enter the interstitium via diffusion, and interstitial ANG II generation is mediated, at least in part, by basolaterally located endothelial ACE.

Effect of brain death and non-heart-beating kidney donation on renal function and injury: an assessment in the isolated perfused rat kidney.

OBJECTIVES: Ischemic injury to the renal allograft prior to implantation is considered as the major cause of primary non and never-function (PNF) and delayed graft function (DGF). Evidence has been put forward that brain dead and non-heart-beating (NHB) donor organs are of marginal quality compared to living donors. The purpose of this study was to evaluate renal function and injury of brain dead and NHB donor kidneys using the isolated perfused rat kidney. MATERIAL AND METHODS: Fisher F344 rats were either maintained brain death for 4 hr or subjected to cardiac arrest for 45 min (NHB). Living rats served as controls. To omit additional effects of cold ischemia, kidneys were immediately reperfused. Renal function and injury were assessed by monitoring urine production, glomerular filtration rate (GFR), Na+ and K+ reabsorption, glucose metabolism and reabsorption, as well as release of brush border, lysosomal, and intracellular enzymes. RESULTS: Renal dysfunction and injury were most pronounced in NHB donor kidneys reflected by a highly reduced urine production, anaerobic glucose metabolism resulting in lactate formation, and significant higher luminal release of intracellular and lysosomal enzymes. Brain dead kidneys showed an increased urine production and were functionally abnormal in K+ reabsorption showing a net excretion of K+, probably as a result of ATP depletion. Loss of brush border occurred during brain death and cardiac arrest. CONCLUSIONS: Both, brain death and cardiac arrest have deleterious effects on renal function and renal injury. The ischemically injured NHB donor kidney was functionally inferior compared to the brain dead donor kidney and living donor kidneys. However, both brain dead and NHB kidneys showed considerable renal damage compared to kidneys from living donors.

Prorenin-induced myocyte proliferation: no role for intracellular angiotensin II.

Cardiomyocytes bind, internalize, and activate prorenin, the inactive precursor of renin, via a mannose 6-phosphate receptor (M6PR)--dependent mechanism. M6PRs couple directly to G-proteins. To investigate whether prorenin binding to cardiomyocytes elicits a response, and if so, whether this response depends on angiotensin (Ang) II, we incubated neonatal rat cardiomyocytes with 2 nmol/L prorenin and/or 150 nmol/L angiotensinogen, with or without 10 mmol/L M6P, 1 micromol/L eprosartan, or 1 micromol/L PD123319 to block M6P and AT(1) and AT(2) receptors, respectively. Protein and DNA synthesis were studied by quantifying [(3)H]-leucine and [(3)H]-thymidine incorporation. For comparison, studies with 100 nmol/L Ang II were also performed. Neither prorenin alone, nor angiotensinogen alone, affected protein or DNA synthesis. Prorenin plus angiotensinogen increased [(3)H]-leucine incorporation (+21 +/- 5%, mean +/- SEM, P<0.01), [(3)H]-thymidine incorporation (+29 +/- 6%, P<0.01), and total cellular protein (+14 +/- 3%, P<0.01), whereas Ang II increased DNA synthesis only (+34 +/- 7%, P<0.01). Eprosartan, but not PD123319 or M6P, blocked the effects of prorenin plus angiotensinogen as well as the effects of Ang II. Medium Ang II levels during prorenin and angiotensinogen incubation were <1 nmol/L. In conclusion, prorenin binding to M6PRs on cardiomyocytes per se does not result in enhanced protein or DNA synthesis. However, through Ang II generation, prorenin is capable of inducing myocyte hypertrophy and proliferation. Because this generation occurs independently of M6PRs, it most likely depends on the catalytic activity of intact prorenin in the medium (because of temporal prosegment unfolding) rather than its intracellular activation. Taken together, our results do not support the concept of Ang II generation in cardiomyocytes following intracellular prorenin activation.