Ischemia/reperfusion (I/R) injury in the kidney involves hemodynamic and cellular dysfunctions as well as leukocyte infiltration. Functional recovery occurs via cell proliferation and/or migration. To determine the roles of hyaluronan (HA) and its main receptor CD44 in renal postischemic processes, we compared their localization and expression with that of neutrophils, macrophages, and PCNApositive (regenerative) cells as characterized by immunohistochemistry, up to 28 days after I/R in uninephrectomized rats. Observations covered all kidney zones, i.e. cortex (C), outer and inner stripes of outer medulla (OSOM, ISOM), and inner medulla (IM). In controls, HA was localized to the interstitium of IM and ISOM, and CD44 was mostly present on the basolateral membranes of collecting ducts in ISOM, the thin descending limb of Henle's loop and macula densa cells. After I/R, HA and CD44 staining appeared in C and OSOM at 12 h and persisted throughout the regenerative period, i.e. until day 7. Thereafter, they regressed but remained associated with remodeling areas. CD44 expression was found de novo on the apical pole of regenerating, not fully differentiated tubular cells and on some interstitial cells. It was prominent on all infiltrating neutrophils, as soon as 2 h post-I/R, and on 30% of the macrophages, including those in late HA-rich inflammatory granulomas. CD44 is probably involved in early leukocyte infiltration, in tubular regeneration, and in macrophage activity, while HA modifies the physico-chemical environment of interstitial and migrating cells. Based on its presence in remodeling areas, the HA-CD44 pair may be implicated in persistent postichemic inflammation as observed in chronic allograft nephropathy.

After the acute inhibition of prostanoid synthesis, adjustments of renal hemodynamics may not be characterized immediately. Therefore, time-related effects of indomethacin on hemodynamics and renal blood flow (RBF) autoregulation were studied in anesthetized euvolemic male rats injected intravenously with vehicle, indomethacin (3, 4, or 5 mg/kg body wt), or meclofenamate (4 or 5 mg/kg body wt). Hemodynamics and RBF autoregulation were not influenced by vehicle injection, nor by time (n = 6). In contrast, mean arterial pressure (MAP) decreased significantly from 117 +/- 4 to 103 +/- 3 mmHg, and RBF progressively and significantly increased from 8.00 +/- 0.34 to 9.17 +/- 0.50 ml/min in the 3 mg/kg body wt indomethacin group (n = 8). Treatment with the higher doses of indomethacin (n = 9) or meclofenamate (n = 6) did not change RBF, while MAP decreased by 15 mmHg. A time-dependent significant enhancement of RBF autoregulatory efficiency was found in the drug-treated rats. Changes in renal function and reductions of prostanoid excretion in urine, of plasma renin activity, or serum aldosterone were similar in the nonsteroidal antiinflammatory drug groups. In conclusion, our findings demonstrate important time-related adjustments of renal hemodynamics in male rats treated with indomethacin, especially with the lower dose (3 mg/kg body wt iv). The factor(s) responsible for the hemodynamic changes remains unknown.

Renal blood flow (RBF) autoregulatory efficiency may be enhanced during NO inhibition in the rat, as recently reported. Under these conditions, endothelin (ET) synthesis and release may be increased. Our purpose was therefore to determine the role of ET in RBF autoregulatory changes induced by NO inhibition. To address this point, ET(A/B) receptors were blocked in anesthetized rats with bosentan, or selectively with BQ-610 or BQ-788. NO synthesis was inhibited with N(G)-nitro-L-arginine methyl ester (L-NAME). Mean arterial pressure (MAP) was decreased after bosentan (-10 mmHg; P < 0.01) or increased after L-NAME (25 mmHg; P < 0.001). RBF measured with an electromagnetic flow probe was reduced by L-NAME (-50%) and by BQ-788 (-24%). The pressure limits of the autoregulatory plateau (P(A) approximately 100 mmHg) and of no RBF autoregulation (P(o) approximately 80 mmHg) were significantly lowered by 15 mmHg after L-NAME but were unchanged after bosentan, BQ-610, or BQ-788. During NO inhibition, autoregulatory resetting was completely hindered by bosentan (P(A) approximately 100 mmHg) and by ET(B) receptor blockade with BQ-788 (P(A) approximately 106 mmHg), but not by ET(A) receptor blockade with BQ-610 (P(A) approximately 85 mmHg). These results suggest that the involvement of ET in the RBF autoregulatory resetting occurs during NO inhibition, possibly by preferential activation of the ET(B) receptor. However, the relative contribution of ET receptor subtypes remains to be further specified.

This study examined the role of intrarenal ANG II in the renal vascular reactivity changes occurring in the remaining kidney undergoing adaptation following contralateral nephrectomy. Renal blood flow responses to intrarenal injections of ANG II (0.25 to 5 ng) were measured in anesthetized euvolemic male Wistar rats 1, 4, 12, and 24 wk after uninephrectomy (UNX) or sham procedure (SHAM). At week 4, renal vasoconstriction induced by 2 ng ANG II was greater in UNX (69 +/- 5%) than in SHAM rats (50 +/- 3%; P < 0.01). This response was inhibited, by 50 and 66%, and by 20 and 25%, in SHAM and UNX rats, after combined injections of ANG II and losartan, or PD-123319 (P < 0.05), respectively. Characteristics of ANG II receptor binding in isolated preglomerular resistance vessels were similar in the two groups. After prostanoid inhibition with indomethacin, renal vasoconstriction was enhanced by 42 +/- 8% (P < 0.05), only in SHAM rats, whereas after 20-HETE inhibition with HET0016, it was reduced by 53 +/- 16% (P < 0.05), only in UNX rats. These differences vanished after concomitant prostanoid and 20-HETE inhibition in the two groups. After UNX, renal cortical protein expression of cytochrome P-450 2c23 isoform (CYP2c23) and cyclooxygenase-1 (COX-1) was unaltered, but it was decreased for CYP4a and increased for COX-2. In conclusion, renal vascular reactivity to ANG II was significantly increased in the postuninephrectomy adapted kidney, independently of protein expression, but presumably involving interactions between 20-HETE and COX in the renal microvasculature and changes in the paracrine activity of ANG II and 20-HETE.

A B S T R A C T Intrarenal transport of urate-2-1'C was studied in anesthetized rats using the microinjection technic. During saline diuresis, small volumes of urate-2-14C (0.24-0.48 mM) and inulin-8H were injected into surface proximal and distal convoluted tubules, and ureteral urine was collected serially. Total (74-96%) and direct (57,84%) urate recovery increased significantly the more distal the puncture site. Delayed recovery (+20%) remained approximately the same regardless of localization of the microinjection. After proximal injections, total and direct recoveries of urate-2-14C were significantly higher in rats treated with probenecid, pyrazinoate, or PAH than during saline diuresis alone, while the excretion rates were comparable after distal injection. Delayed recovery was not altered by drug administration. The decreased proximal reabsorption of urate is presumably due to an effect of the drugs on the luminal membrane of the nephron. For perfusion at high urate concentrations, nonradioactive urate was added to the injectate (0.89-1.78 mM). Urate-2-14C recovery was almost complete and there was no delayed excretion, demonstrating saturation kinetics. These findings are compatible with a carriermediated mechanism for urate transport probably located at the luminal border of the proximal tubular epithelium. No definitive evidence for urate secretion was found in these studies. INTRODUCTIONAlthough the renal excretion of urate has been extensively studied, the site(s) and mechanism(s) for urate