Effects of atrial natriuretic factor, nitroprusside and acetylcholine on cGMP immunostaining in the isolated perfused rat kidney

Sildenafil attenuates renal ischemia reperfusion injury by decreasing leukocyte infiltration

The aim of the study was to investigate the effects of sildenafil citrate (SC) on renal ischemia reperfusion (I/R) injury in a rat model. Forty eight male Wistar albino rats were randomly assigned into six groups: sham, ischemia, I/R, SC+sham, SC+ischemia and SC+I/R. In the I/R groups, the right kidney was removed and the artery and vein of the left kidney were clamped for 45 min followed by reperfusion for 1 h. In the SC-treated groups, SC dissolved in saline solution was given as a single dose (1 mg/kg) 60 min before the operation. Renal histology was analyzed by scoring the tubular damage and neutrophil infiltration. Tissue myeloperoxidase activity and lipid peroxidation were analyzed. The histological damage and the neutrophil infiltration induced by I/R were significantly less in the SC+I/R group (p = 0.004 and p = 0.003, respectively). Pretreatment with SC significantly diminished the tissue myeloperoxidase activity, indicating the prevention of the neutrophil sequestration into the kidney in the SC+I/R group (p = 0.004); however, it did not result in any changes in lipid peroxidation. Our results in a rat model of ischemia-reperfusion indicate that pre-ischemic treatment with sildenafil citrate can significantly attenuate ischemia/reperfusion-induced renal injury by decreasing leukocyte infiltration.

Role of macula densa nitric oxide and cGMP in the regulation of tubuloglomerular feedback

BACKGROUND

Previous studies have suggested that nitric oxide (NO) produced within cells of the macula densa (MD) modulates tubuloglomerular feedback (TGF). We tested the hypothesis that NO produced in the MD acts locally as an autacoid to activate soluble guanylate cyclase and cGMP-dependent protein kinase in the MD itself.

METHODS

Rabbit afferent arterioles (Af-Arts) and attached MD were simultaneously microperfused in vitro. The TGF response was determined by measuring the Af-Art diameter before and after increasing NaCl in the MD perfusate (from 17 mmol/L of Na and 2 of Cl to 65 mmol/L of Na and 50 of Cl). TGF was studied before (control TGF) and after inhibiting components of the NO-cGMP-dependent cascade in the tubular or vascular compartment.

RESULTS

Increasing NaCl concentration in the MD perfusate decreased the Af-Art diameter by 3.2 +/- 0.5 microm (from 18.5 +/- 1.3 to 15.4 +/- 1.3 microm, P < 0.001). Adding a soluble guanylate cyclase inhibitor (LY83583) to the MD increased TGF response to 6.3 +/- 1.1 microm (P < 0.031 vs. control TGF). Similarly, when cGMP-dependent protein kinase was inhibited with KT5823, TGF was augmented from 2.6 +/- 0.3 to 4.0 +/- 0.7 microm (P < 0.023). An analogue of cGMP in the MD reversed the TGF-potentiating effect of both 7-nitroindazole (7NI; an nNOS inhibitor) and LY83583. Inhibition of MD guanylate cyclase did not alter the effect of acetylcholine (a NO-cGMP-dependent vasodilator) on the Af-Art. Perfusing the Af-Art with the guanylate cyclase inhibitor did not potentiate TGF, suggesting that the effect of NO occurred at the MD via a cGMP-dependent mechanism. To determine whether the effect of NO in the MD was entirely mediated by cGMP, TGF was studied after giving (1) LY83583 or (2) LY83583 plus 7NI. Adding the nNOS inhibitor to the MD did not potentiate the TGF response further.

CONCLUSIONS

We concluded the following: (1) NO produced by the MD inhibits TGF via stimulation of soluble guanylate cyclase, generating cGMP and activating cGMP-dependent protein kinase; (2) NO acts on the MD itself rather than by diffusing to the Af-Art; and (3) most, if not all, of the effect of NO in the MD is due to a cGMP-dependent mechanism rather than to other NO mediators.