Characterization of renin mRNA expression and enzyme activity in rat and mouse mesangial cells

Renin is an enzyme involved in the stepwise generation of angiotensin II. Juxtaglomerular cells are the main source of plasma renin, but renin activity has been detected in other cell types. In the present study we evaluated the presence of renin mRNA in adult male Wistar rat and mouse (C-57 Black/6) mesangial cells (MC) and their ability to process, store and release both the active and inactive forms of the enzyme. Active renin and total renin content obtained after trypsin treatment were estimated by angiotensinogen consumption analyzed by SDS-PAGE electrophoresis and quantified by angiotensin I generation by HPLC. Renin mRNA, detected by RT-PCR, was present in both rat and mouse MC under basal conditions. Active renin was significantly higher (P<0.05) in the cell lysate (43.5 +/- 5.7 ng h-1 10(6) cells) than in the culture medium (12.5 +/- 2.5 ng h-1 10(6) cells). Inactive prorenin content was similar for the intra- and extracellular compartments (9.7 +/- 3.1 and 3.9 +/- 0.9 ng h-1 10(6) cells). Free active renin was the predominant form found in both cell compartments. These results indicate that MC in culture are able to synthesize and translate renin mRNA probably as inactive prorenin which is mostly processed to active renin inside the cell. MC secrete both forms of the enzyme but at a lower level compared with intracellular content, suggesting that the main role of renin synthesized by MC may be the intracellular generation of angiotensin II

Heterogeneity of glomerular perfusion and filtration induced by epinephrine and norepinephrine

The role of catecholamines in the distribution of intrarenal blood flow and in single-nephron glomerular filtration rate (SNGFR) was evaluated in anesthetized Wistar rats by the Hanssen technique. Epinephrine (EPI) and norepinephrine (NOR) were infused to produce elevations of 20-30 mmHg in mean arterial pressure. Superficial and juxtamedullary nephron perfusion and filtration were determined by the presence of Prussian blue dye. In the control group, 100 per cent of the nephrons presented a homogeneous pattern of perfusion and filtration. In contrast, a heterogenous distribution of the dye was found even in the larger arteries (arciform and radial), indicating variable perfusion and filtration in both superficial and juxtamedullary nephrons. The effects of EPI and NOR were also evaluated in the superficial cortex by the micropuncture technique in two additional groups of Munich-Wistar rats. Mean SNGFR was 27 per cent and 54 per cent lower in the EPI-and NOR-treated groups, respectively. No change in mean intraglomerular hydraulic pressure was observed after EPI or NOR infusion in spite of a highly scattered pattern, indicating an important variability in perfusion along the superficial cortex, and/or different sensitivity of the pre-and post-glomerular arterioles. The present data suggest that EPI and NOR may affect intrarenal hemodynamics by modifying perfusion and filtration in both superficial and juxtamedullary glomeruli and not by shifting blood folow from superficial to juxtamedullary nephrons. The heterogenous pattern of perfusion was a consequence of differential vasoconstriction along the intrarenal arteries, probably due to different density and/or sensitivity of the adrenergic receptor subtypes present in the intrarenal vascular tree.

Glomerular hemodynamics during abortion induced by RU 486 and sepsis in rats

1. Acute renal failure is a very common consequence of septic abortion. Whole kidney and glomerular hemodynamics were evaluated in virgin (V), pregnant (PREG) and aborted (ABOR) euvolemic Munich-Wistar rats before and after E. coli (0111-B4) endotoxin (LPS) infusion in order to evaluate the effect of septic abortion on the renal microcirculation. 2. Abortion induced by RU 486 blunted the increase in glomerular filtration rate (GFR) induced by normal pregnancy (0.86 +/- 0.03 vs 0.63 +/- 0.07 ml/min, P < 0.05). In virgin rats, RU 486 did not modify the parameters of renal function. Significant alterations occurred in whole kidney and single nephron function. However, the changes in whole kidney function in the ABOR group were significantly higher than those observed for the V group (reductions in GFR were 42 in V and 80 in ABOR, RPF decreased 34 in V and 76 in ABOR, TRVR increased 82 in V and 400 in ABOR). 3. Mean single nephron glomerular filtration rate (SNGFR) was reduced in all groups after LPS (44 in V, 43 in V+RU, 55 in PREG, 60 in ABOR), due to significant decreases in glomerular plasma flow rate, QA (42 in V, 55 in V+RU, 53 in PREG, 57 in ABOR) and in glomerular ultrafiltration coefficient, Kf (46 in V, 47 in V+RU, 45 in PREG, 67 in ABOR). 4. These data show that LPS induced significant alterations in renal function in all groups. However, aborted rats were more sensitive to the effects of LPS than V rats. These results indicate that abortion may potentiate the effects of endotoxemia on renal function elevating the extent of acute renal failure and thus the mortality rate.

Effect of time on remnant glomerular function

1. Although hypertrophy and hyperfiltration have been identified in remnant nephrons, the time of their appearance and the relationship between them have not been established. In order to evaluate remnant glomerular hemodynamics over different periods of time, we studied Munich-Wistar rats 7, 30 and 60 days after 5/6 renal mass ablation. 2. Kidney weight increased after 7 days, continued to increase after 30 days and decreased after 60 days. Glomerular filtration rate (GFR) and renal plasma flow decreased by 67 per cent and 7 days, were 35 per cent lower than normal after 30 days, and after 60 days presented the same values as after 7 days. Single-nephron GFR and glomerular plasma flow increased slightly after 7 days, were 118 per cent higher than control after 30 days, and decreased after 60 days. Hydraulic glomerular capillary pressure tended to increase after 30 days (6 per cent ), reaching statistical significance after 60 days (45 vs 62 mmHg). The glomerular ultrafiltration coefficient increased significantly after 30 days (82 per cent ) and decreased to values similar to the control group after 60 days. 3. These data suggest that kidney hypertrophy occurs early after reduction of renal mass, before the hemodynamic adaptations are complete. Glomerular hypertension was observed after 60 days, when single-nephron GFR and the glomerular ultrafiltration coefficient were decreased compared to rats studied after 30 days. 4. These data may indicate that, once glomerular hypertension starts, structural abnormalities are followed by a decline in glomerular function

Effect of cicletanine on the progression of chronic renal failure in rats

1. The effects of chronically administered cicletanine (CICL), an antihypertensive and prostacyclin stimulating agent, on glomerular hemodynamics were evaluated after 30 (CRF-30) or 60 (CRF-60) days of chronic renal failure (CRF) induced by 5/6 nephrectomy in Munich-Wistar rats. 2. CICL administration (3 mg kg-1 day-1, N = 5) for 60 days did not modify glomerular hemodynamics of normal rats (control group). The CRF-60 group (N = 6) presented a significant increase in mean arterial pressure (MAP) compared with control (122 +/- 7 vs 98 +/- 2 mmHg, P < 0.05), which was attenuated by CICL (113 +/- 7 vs 122 +/- 7 mmHg). 3. Hyperfiltration and hyperperfusion were observed in both CRF groups after 30 (N = 5) but not after 60 days of CRF, 73.9 +/- 6.3 and 48.2 +/- 3.2 vs 36.8 +/- 2.6 nl/min for SNGFR and 200 +/- 17 and 147 +/- 8 vs 112 +/- 8 nl/min for QA in CRF-30, CRF-60 vs control group, respectively. However, glomerular hypertension was demonstrable for both CRF groups only after 60 days. CICL treatment starting 7 days prior to nephrectomy reduced the transcapillary hydraulic pressure difference (delta P) in both groups, 36 +/- 3 vs 30 +/- 2 mmHg (30 days) and 41 +/- 4 vs 34 +/- 2 (60 days), but did not significantly modify arteriolar resistances or glomerular hemodynamics, suggesting that the reduction in MAP in response to CICL may have been responsible for the decrease in delta P. CICL administration did not prevent the proteinuria or glomerular sclerosis associated with CRF. 4. The results suggest that the administration of CICL for 30 (N = 4) to 60 days (N = 7) was sufficient to prevent systemic hypertension associated with CRF but not to reduce the additional glomerular hemodynamic factors that participate in the progression of CRF

Renal sodium conservation during starvation in rats

The natriuresis of fasting has been well characterized in man and rabbits but not in rats. The daily effects of fasting on glomerular filtration rate (GFR) and urinary sodium and potassium excretion were evaluated in Munich-Wistar rats (260-310 g) submitted to prolonged starvation (2-8 days). Rats do not present the natriuresis of fasting. Sodium excretion was reduced since the first few hours (0-4 h) of starvation. Antinatriuresis was abrupt during the early periods (1st and 2nd days) and stabilized at very low levels. During the early phase (4 days), sodium retention occurred due to both reduced glomerular filtration and increased tubular reabsorption. However, during the late phase (after the 4th day), antinatriuresis was mainly induced by the elevation in tubular reabsorption, since a normalization of GFR was observed. Thus, these homeostatic mechanisms permit adequate renal sodium conservation during starvation in rats

Effect of cisplatin on glomerular hemodynamics

The effects of cisplatin on renal microcirculation were evaluated in euvolemic Munich-Wistar rats submitted to micropuncture. Nine rats received a single dose of cisplatin (6 mg/kg,ip), and 6 control rats received the same volume (0.3 ml) of 15 mM NaCl 4 days before the measurements. Cisplatin administration induced non-oliguric acute renal failure by decreasing glomerular filtration rate (GFR) from 0.96 + or- 0.5 to 0.33 + or - 0.04 ml/min (P<0.05) and by increasing urinary volume from 3.3 + or - 0.3 to 12.4 + or - 2.2 micronl/min (P<0.05). Cisplatin administration decreased single nephron GFR from 34.2 + or - 2.1 to 20.1 + or - 2.3 nl/min (P<0.05) due to a reduction in both glomerular plasma flow from 106 + or - 9 to 61 + or - 6 nl/min (P<0.05) and transcapillary hydraulic pressure difference from 31 + or - 1 to 27 + or - 1 mmHg (P<0.05). An increase in arteriolar resistances, mainly afferent arteriolar resistance from 2.5 + or - 0.2 to 4.7 + or - 0.5 x 10**10 dyn.s.cm**-5 (P<0.05), was observed. The glomerular ultrafiltration coefficient was unchanged