Dietary protein restriction in established renal injury in the rat. Selective role of glomerular capillary pressure in progressive glomerular dysfunction.

Dietary protein restriction imposed before renal injury is established in the remnant kidney model in the rat reduces glomerular hypertension and hyperperfusion and renal injury. We demonstrate that dietary protein restriction (6% vs. 20%) imposed on a background of established renal injury in the remnant model leads to a greater preservation of renal function as measured by glomerular filtration rate and fractional clearances of albumin and IgG, despite the persistence of systemic hypertension. In similarly prepared rats, dietary protein restriction (6% vs. 20%) led to a lower glomerular capillary hydraulic pressure, a higher ultrafiltration coefficient, and similar single nephron filtration rates. In addition, less impairment of glomerular permselectivity was demonstrable after protein restriction. Our data demonstrate that the preservation of renal function with dietary protein restriction after established glomerular injury follows upon reduction of glomerular capillary hydraulic pressure, despite constancy of single nephron filtration rate and plasma flow and persistence of arterial hypertension.

Role of aldosterone in the remnant kidney model in the rat.

The renin-angiotensin-aldosterone system (RAAS) participates in the injury sustained by the remnant kidney. Our studies assessed the importance of aldosterone in that model and the response of aldosterone to drugs interfering with the RAAS. Initially, four groups of rats were studied: SHAM-operated rats, untreated remnant rats (REM), REM rats treated with losartan and enalapril (REM AIIA), and REM AIIA rats infused with exogenous aldosterone (REM AIIA + ALDO). The last group was maintained with aldosterone levels comparable to those in untreated REM rats by constant infusion of exogenous aldosterone. REM rats had larger adrenal glands and a > 10-fold elevation in plasma aldosterone compared to SHAM. REM AIIA rats demonstrated significant suppression of the hyperaldosteronism as well as marked attenuation of proteinuria, hypertension, and glomerulosclerosis compared to REM. REM AIIA + ALDO rats manifested greater proteinuria, hypertension, and glomerulosclerosis than REM AIIA rats. Indeed, by 4 wk of observation all of these features of the experimental disease were similar in magnitude in REM AIIA + ALDO and untreated REM. In separate REM rats spironolactone administration did not reduce glomerular sclerosis but did transiently reduce proteinuria, lowered arterial pressure, and lessened cardiac hypertrophy. In summary, aldosterone contributes to hypertension and renal injury in the remnant kidney model.

Aldosterone is a major factor in the progression of renal disease.

There is compelling evidence supporting the renin-angiotensin-aldosterone system contribution in experimental and human renal disease. Interruption of this system by converting enzyme inhibition or angiotensin II receptor antagonism reduces injury. Angiotensin II contributes to the progression of renal disease through its direct vascular effects and proliferative properties. The mediators of angiotensin II induced renal injury are many and include TGF-beta, PDGF, bFGF, and endothelin. Though the mechanisms involved in its contribution to progressive renal disease are not well delineated, aldosterone seems to be an overlooked contributor to the progression of kidney disease and its effects may also depend on both its hemodynamic and more direct cellular actions.

The course of the remnant kidney model in mice.

The remnant kidney model was produced in mice by unilateral nephrectomy and partial infarction of the remaining kidney. Control mice underwent laparotomy only. The mice were studied for up to 44 weeks. No quantitative differences were noted in systolic arterial pressure, proteinuria, or histopathology between control mice and those with a remnant kidney. Glomerular enlargement occurred in the remnant kidney.

Effect of dietary protein on the renin-angiotensin system in subtotally nephrectomized rats.

Dietary protein restriction improves the course of renal disease in the remnant kidney model. Dietary protein restriction can also reduce plasma renin activity in several circumstances. We examined the interaction between dietary protein and the renin-angiotensin system in subtotally nephrectomized rats (1-2/3 nephrectomy). No difference was seen in tissue renin activity in rats ingesting a high (30%) versus a low (6%) protein diet. To determine the pathophysiological role of angiotensin II in subtotally nephrectomized rats, we examined the acute renal response to an intrarenal infusion of the angiotensin II antagonist Sar1 Gly8-angiotensin II (10 micrograms/kg/min). Only those subtotally nephrectomized animals ingesting a high protein diet exhibited a consistent improvement in glomerular permselectivity, as manifested by a 24% fall in the fractional clearance of albumin (basal 16.19 +/- 3.65 x 10(-4) vs. Sar1 Gly8-AII 12.26 +/- 3.21 x 10(-4); P less than 0.02) and a 19% fall in the fractional clearance of IgG (basal 3.75 +/- 0.67 x 10(-4) vs. Sar1 Gly8-AII 3.03 +/- 0.48 x 10(-4); P less than 0.02). No consistent change occurred in glomerular permselectivity in the rats on the low protein diet or rats infused with vehicle only. No change in mean arterial pressure or whole-kidney hemodynamics were seen with angiotensin II blockade. Decrements in SNGFR and glomerular capillary pressure occurred with angiotensin blockade in the animals ingesting the high protein diet, suggesting hemodynamic factors as a mechanism for the improvement in permselective defects.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiological and structural responses to chronic experimental renal allograft injury.

Chronic rejection necessitates a return to dialysis or retransplantation for a significant number of patients with renal allografts. Although alloresponses between donor organ and recipient importantly determine this process, the detailed immunologic processes and organ physiology of chronic rejection are unclear; in consequence its mechanism and therapy are uncertain. A model of chronic rejection in the rat was used to examine several facets of this process. Fisher-to-Lewis (F-L), allogeneic, and Lewis-to-Lewis (L-L), syngeneic, renal transplants were performed in nephrectomized recipients. All rats were treated with cyclosporin A (5 mg.kg-1.day-1) for 10 days from the time of grafting. At 6 wk, allogeneically grafted animals had a higher protein excretion rate (F-L, 47 +/- 30 mg/day; L-L, 17 +/- 6 mg/day; P < 0.05) and an increase in glomerular capillary pressure (F-L, 69 +/- 5 mmHg; L-L, 58 +/- 8 mmHg; P < 0.05) and fractional cortical interstitial volume (F-L, 29.8 +/- 4.3%; L-L, 19.5 +/- 4.0%; P < 0.01). This model of chronic rejection is characterized by glomerular capillary hypertension, proteinuria, and cortical interstitial expansion. Because these findings are also present in other models of chronic renal injury, mechanisms in addition to alloresponses may operate in chronic rejection.

Glomerular renin synthesis and storage in the remnant kidney in the rat.

The intrarenal renin-angiotensin system can exert local control of the nephron and its circulation. In the subtotally nephrectomized model of chronic renal disease in the rat, angiotensin appears to play a prominent role in glomerular function. Glomeruli in this model demonstrate greater staining for intraglomerular renin by immunofluorescence microscopy than do those in control rats. Glomeruli from remnant nephrons contain increased renin content. Also, glomeruli from remnant nephrons contain an increased proportion of the mRNA for renin. Adriamycin-induced nephrosis did not evoke the same degree of renin staining and did not lead to increased glomerular expression of the renin gene, findings that argue against permselective defects and glomerular trapping as the sole cause of the glomerular renin in the remnant kidney model. Thus, renin synthesis and accumulation occur in the remnant glomerulus and this migration may underlie in part the dependence of glomerular function on the renin-angiotensin system in this model.