Shapira J

Effect of Tetrahydrobiopterin on Blood Pressure in Rats after Subtotal Nephrectomy

Background: Previous studies have shown that endothelial dysfunction after 5/6 nephrectomy (5/6 Nx) in rats is associated with decreased nitric oxide (NO) bioavailability and increased vascular superoxide production. Blood pressure is significantly increased by day 10 after surgery. Tetrahydrobiopterin (BH4) is a key cofactor of NO synthase. Suboptimal levels of BH4 result in uncoupling of NO synthase, low NO synthesis and augmented production of superoxide anions. The aim of this study was to evaluate whether BH4 supplementation may improve NO production and prevent the increase of blood pressure after 5/6 Nx. Methods: Three groups were evaluated: 5/6 Nx (untreated rats), BH4 (5/6 Nx rats treated with BH4, 10 mg/day i.p. for 10 days) and L-ARG (5/6 Nx rats treated with L-arginine, 260 mg/kg BW, p.o for 10 days). Systolic blood pressure (SBP), urinary nitrate excretion (UNO3) and creatinine clearance (CCR) were measured before surgery and on days 3 and 10 after surgery. Endothelial NO synthase (eNOS) protein content of mesenteric resistance vessels was measured at the end of the study. Results: SBP increased from 107 ± 2 to 127 ± 4 mm Hg in untreated 5/6 Nx rats (p < 0.01). By contrast, rats treated with BH4 or L-ARG remained normotensive. Ten days after 5/6 Nx, creatinine clearance decreased similarly in all groups. Both BH4 and L-ARG supplementation markedly increased UNO3 excretion. The mesenteric vascular expression of eNOs protein was significantly higher in BH4 but not in L-ARG, compared with Nx rats. Conclusions: BH4 supplementation prevents the earlier increase in blood pressure observed in rats after 5/6 Nx, possibly by upregulating eNOS in resistance vessels.

Captopril, but not diltiazem, favorably affects the course of early chronic renal disease in rats

The concepts that increased intracellular Ca2+ content and increased glomerular capillary pressure play an important role in the progression of chronic renal diseases has led to the suggestion that treatment with calcium-blocking agents (diltiazem; CBB) or converting enzyme inhibitors (captopril; CEI) may be indicated to prevent renal failure. We studied the effects of CCB and CEI on the early course of adriamycin (ADR) nephropathy, where glomerular pressure has been shown to be unchanged, blood pressure was only mildly elevated and renal failure incipient. Animals were studied 2, 7, 12, 16 and 20 weeks after the second injection of ADR, 2 mg/kg. In treated rats, blood pressure remained normal. At the end of the study, proteinuria and serum creatine were lower in ADR-CEI than in ADR rats (149 +/- 42 vs. 616 +/- 90 mg/day, p less than 0.01 and 0.36 +/- 0.04 vs. 0.58 +/- 0.02 mg%, p less than 0.01, respectively). ADR-CCB had values similar to those of untreated ADR rats. Mesangial expansion and focal glomerulosclerosis were present only in ADR and ADR-CCB rats, whereas in ADR-CEI rats the glomeruli were virtually normal. Glomerular 45Ca uptake was increased in ADR, decreased in ADR-CCB rats, and normal in ADR-CEI. Glomerular 6-keto PGF1 alpha and TxB2 were significantly increased in ADR rats, and both treatments decreased TxB2. The results suggest that endogenous angiotensin II is important for the early progression of glomerular injury toward renal insufficiency, while tissue Ca2+ accumulation may play an important role in more advanced phases.

Changes in Renal Prostanoid Synthesis Induced by Potassium Loading in Rats

Previous works have demonstrated changes in the urinary excretion of prostaglandins (PG) in response to changes in potassium (K) or sodium (Na) intake. In the present study, the production of PGE2, PGF2 alpha, 6-keto-PGF1 alpha and thromboxane B2 (TXB2) by isolated glomeruli, cortical homogenates, medullary and papillary slices was measured in K-loaded rats on either a normal or a low Na intake. In glomeruli, K loading increased selectively PGE2 synthesis. In Na-depleted animals, all prostanoids were elevated and K loading did not induce a further increase. In cortical and medullary preparations, PGE2 was decreased by K loading irrespective of the state of Na balance. In papilla, PGE2 decreased (in all K-loaded rats) and PGF2 alpha increased (only in rats with normal Na intake). 6-Keto-PGF1 alpha and TXB2 did not change significantly. No correlation was present between changes of PG synthesis and urinary kallikrein excretion. The results demonstrate a specific effect of K on PGE2 and PGF2 alpha, and suggest a role for these substances in K homeOstasis.

Urinary Prostaglandins E2 and F2α in Chronic Renal Failure

The role played by renal prostaglandins E2 (PGE2) and F2 alpha (PGF 2 alpha) in the modification of sodium homeostasis in chronic renal failure (CFR) was studied. The 24-hour urinary excretion of PGE2 and PGF2 alpha was measured before and after 5 days of a diet containing less than 20 mmol/day of sodium in 6 patients with CRF. At the end of this period, an acute sodium load (77 mmol/h of NaCl for 4 h) was administered and prostaglandins measured in hourly urine collections. In contrast to the findings previously reported in normal subjects, PGE2 and PGF2 alpha decreased with the low-sodium diet. The ratio PGE2/PGF2 alpha (reflecting the activity of the enzyme PGE2-9-ketoreductase) was greatly increased and did not change with the low-sodium diet. The acute sodium load induced an increase in urinary prostaglandins. The results suggest that prostaglandins may contribute to natriuresis in CRF, under basal conditions, after a short-term sodium depletion and in response to an acute sodium load. The changes in prostaglandin excretion in CRF could be related to decreased activity of PGE2-9-ketoreductase.The role played by renal prostaglandins E2 (PGE2) and F2α(PGF2α) in the modification of sodium homeostasis in chronic renal failure (CFR) was studied. The 2

Thrombin Inhibits the Synthesis of Prostanoids by Isolated Glomeruli and Peritoneal Macrophages in Rats

Activation of macrophages and release of mediators that activate the coagulation system characterize proliferative glomerulonephritis. To evaluate the possible role of prostanoids in this process, isolated rat glomeruli (G) and peritoneal macrophages (M) or a combination of the two (G + M) were incubated in the presence of thrombin (2 U/ml). In G, thrombin inhibited only the synthesis of thromboxane B2. In M and G + M incubations, the synthesis of prostaglandin I2 and thromboxane A2 was inhibited by thrombin. This effect was abolished by the addition of arachidonic acid. As prostanoids may play a modulatory role in the interaction between macrophages and glomerular cells, inhibition of their synthesis by thrombin might enhance macrophage activity.

Late Treatment with Captopril Worsens the Course of Adriamycin Nephropathy in Rats

High blood pressure, increased calcium deposition, enhanced glomerular capillary pressure may all have a significant role in the progression of chronic renal diseases (1). It was recently proposed that converting enzyme inhibitors may prevent or delay the occurence of renal failure but results are controversial (2). The effect of these drugs could be related to their antihypertensive action or to specific local influences(2). Most studies have been performed in rats, after subtotal nephrectomy, a model with marked hyperfiltration, severe systemic hypertension and moderate renal failure (3). In the present investigation we studied the effects of Captopril (converting enzyme inhibitorCEI), administered at different stages, in adriamycin (ADR)-induced nephropathy. This is a recently described model, adequate for long term studies, which shares some similarities with human nephropaties (4).