Abstract-The cause of focal-segmental glomerulosclerosis as a consequence of physiological aging, which is believed to be inexorable, is unknown. This study investigated whether inhibition of endothelin-1, a growth-promoting peptide contributing to renal injury in hypertension and diabetes, affects established glomerulosclerosis and proteinuria in the aged kidney. We also determined the role of endothelin receptors for podocyte injury in vivo and in vitro. Aged Wistar rats, a model of spontaneous age-dependent glomerulosclerosis, were treated with the orally active endothelin subtype A (ET A ) receptor antagonist darusentan, and evaluation of renal histology, renal function studies, and expression analyses were performed. In vitro experiments using puromycin aminonucleoside to induce podocyte injury investigated the role of ET A receptor signaling for apoptosis, cytoskeletal injury, and DNA synthesis. In aged Wistar rats, established glomerulosclerosis and proteinuria were reduced by Ͼ50% after 4 weeks of darusentan treatment, whereas blood pressure, glomerular filtration rate, or tubulo-interstitial renal injury remained unaffected. Improvement of structural injury in glomeruli and podocytes was accompanied by a reduction of the expression of matrix metalloproteinase-9 and p21 Cip1/WAF1 . In vitro experiments blocking ET A receptors using specific antagonists or RNA interference prevented apoptosis and structural damage to podocytes induced by puromycin aminonucleoside. In conclusion, these results support the hypothesis that endogenous endothelin contributes to glomerulosclerosis and proteinuria in the aging kidney. The results further suggest that age-dependent glomerulosclerosis is not merely a "degenerative" but a reversible process locally confined to the glomerulus involving recovery of podocytes from previous injury. Key Words: arterial presure Ⅲ nephrosclerosis Ⅲ DNA Ⅲ kidney failure Ⅲ renal artery Ⅲ expression Ⅲ kidney Ⅲ renal disease A ging represents an important factor determining onset and course of disease and has become a significant issue in view of the anticipated increase of the aging population. Aging in humans and rodents progressively impairs renal function 1,2 and structure, the latter of which is characterized by damage of podocytes and mesangial matrix, as well as capillary hypertrophy and obliteration resulting in glomerulosclerosis. 2 The exact mechanisms underlying agedependent renal injury are unknown. In otherwise healthy individuals Ն65 years of age, even in the absence of known risk factors such as hypertension or diabetes, glomerulosclerosis is frequently present. 3 Currently, Ϸ1.4% of the US total population is affected, and the incidence is expected to increase to Ͼ2% within the next 15 years. 3 Glomerulosclerosis and proteinuria involve injury of podocytes, also known as glomerular epithelial cells that maintain an intact filtration barrier and control glomerular basement membrane turnover under normal conditions. 4 -7 In addition to cell-specific changes during aging, cell c...

We have developed a new preparation for in vivo visualization of the glomerular microcirculation, the vas afferens and the vas efferens. This preparation utilizes postischemic hydronephrosis (PIH) to destroy the renal tubular system while preserving a portion of the cortex. In this preparation, glomeruli and associated vasculature remained intact. Observations can be made with either incident light or transillumination. The inner diameter of the vas afferens, measured within 50 microns of the glomerular vascular pole, was 7.9 +/- 0.5 microns (N = 12; SEM) while that of the vas efferens was 7.7 +/- 0.5 microns (N = 12). Both vessels were narrower adjacent to the glomerulus; minimal diameters in this region were 4.5 +/- 0.5 microns (N = 10) and 4.3 +/- 0.5 microns (N = 11), respectively. A specialized round cell, which may act as a sphincter, was seen in the vas efferens. In a second series of experiments, blood velocity was measured in the vas afferens and efferens about 100 microns from the vascular pole. Mean control velocities at these sites were 5.9 +/- 0.9 (N = 14) and 4.6 +/- 1.3 (N = 9) mm X sec-1, respectively; diameters at these same sites were 10.3 +/- 0.6 microns and 11.2 +/- 0.7. During angiotensin II infusion (first series, 0.2 to 0.4 micrograms X min-1 X kg-1, i.v.) the vas efferens in the vicinity of the glomerulus constricted by 22% whereas the corresponding vas afferens showed no consistent response. During angiotensin II infusion, the filtration fraction (GFR/RPF) may, therefore, be elevated by an increased resistance in the vas efferens, particularly at the outflow point of the glomerulus. In the second series of experiments higher dosages of angiotensin II caused vasoconstriction of both vessels, especially at sites more distant from the glomerulus. Furthermore, the new approach is suitable for observing the flow direction within single capillaries of one third to one half of the glomerulus. Therefore, for the first time it is possible to determine the real flow direction in a three-dimensional way.

This study investigated effects of renal prostaglandins and their interaction with different vasoactive agents in regulating regional renal blood flow. Using intravenous infusions, we compared effects of different pressor hormones and a nitric oxide (NO) inhibitor under control conditions and after inhibition of cyclooxygenase. Because vasodilator effects of prostanoids are considered to be mediated via opening of ATP-dependent K+ channels, we also studied effects of a prostacyclin analogue (iloprost), a channel opener (lemakalim), and a channel blocker (glibenclamide). Blood flow in renal cortex (CBF) and medulla (MBF) was determined with previously described platinum electrodes inserted into the kidney of anesthetized rats. Angiotensin II and norepinephrine reduced predominantly only CBF (-24 and -19%, respectively). After indomethacin, which selectively reduced MBF (-25%), angiotensin II and norepinephrine also reduced MBF (-45 and -35%, respectively), whereas the corresponding changes in CBF were not affected by indomethacin. Arginine vasopressin and the NO inhibitor NG-nitro-L-arginine methyl ester reduced both CBF and MBF by approximately 30% both under control conditions and after indomethacin. Iloprost and lemakalim increased selectively MBF (15 and 27%, respectively), whereas glibenclamide selectively decreased MBF (-19%). Our data indicate that renal prostaglandins are predominantly involved in regulating medullary circulation. They probably exert their dilatory action on medullary vessels via opening of ATP-dependent K+ channels and are involved in antagonizing medullary effects of pressor hormones in an agonist-specific manner.