Janice Green

Pregnancy-Induced Hypertension in Rats With Adriamycin Nephropathy Is Associated With an Inadequate Production of Nitric Oxide

Hypertensive complications are relatively common in pregnancy, particularly in the presence of preexisting renal disease. Although the pathogenesis of such complications is still unknown, recent animal studies have suggested that it may be related to impaired synthesis of nitric oxide (NO). Rats with adriamycin nephropathy develop a preeclamptic-type pregnant state characterized by elevated blood pressure, lack of hyperfiltration, and enhanced proteinuria. Preliminary studies with this model have implicated inadequate NO synthesis in the development of preeclamptic-like pregnancy. The aim of the present study was to confirm this hypothesis. Pregnant rats, both normal (PREG) and those with adriamycin nephropathy (AN-PREG), received 100 mg/L N omega-nitro-L-arginine methyl ester PO from the middle of gestation to term (day 11, term approximately 22 days). One group of AN-PREG rats received either L-arginine or D-arginine (2 g/L) from midpregnancy. At term, systolic pressure, mean arterial pressure, urinary metabolites of NO, creatinine clearance, and urinary protein were assessed. At term, compared with virgin rats with adriamycin nephropathy, untreated AN-PREG rats had increased systolic pressure, mean arterial pressure, and proteinuria (mean arterial pressure, 124 +/- 2.5 versus 99.7 +/- 1.6 mm Hg [P < .05]; proteinuria, 434 +/- 58 versus 216 +/- 63 mg/d [P < .05]). Creatinine clearance did not change (1.68 +/- 0.23 versus 1.35 +/- 0.09 mL/min, P = NS). In PREG rats, urinary metabolites of NO increased approximately threefold at term pregnancy compared with control. By contrast, in AN-PREG rats, excretion of urinary metabolites of NO increased only by approximately 1.7-fold (P < .01) versus PREG rats. With the exception of AN-PREG rats, inhibition of NO synthesis with N omega-nitro-L-arginine methyl ester enhanced blood pressure and decreased creatinine clearance but did not influence proteinuria. Excretion of urinary metabolites of NO was similarly inhibited in all rats. In AN-PREG rats, L-arginine normalized blood pressure (91 +/- 2.15 mm Hg) and lowered proteinuria partially but significantly. D-Arginine had no effect. In summary, AN-PREG rats are unable to adequately increase NO synthesis when physiologically required. Correction of this deficit by L-arginine treatment induced a significant clinical improvement.

Effect of Methyldopa on Renal Function in Rats with L-NAME-Induced Hypertension in Pregnancy

Background: Pregnancy-induced hypertension is characterized by an increased sympathetic activity and probably by a decreased synthesis/activity of nitric oxide. The aim of the present study is to evaluate whether the beneficial action of the sympathetic antagonist methyldopa (a first-choice hypotensive agent in the treatment of PIH) may be associated to changes in nitric-oxide synthesis. Methods: Forty pregnant Wistar rats received L-NAME (NO synthase inhibitor, 9–10 mg/kg/day) from mid-pregnancy (day 11) through to term. Some rats were treated with daltroban (TxA receptor antagonist, 60 mg/kg/day), diltiazem (calcium channel blocker, 30 mg/kg/day), methyldopa (central adrenergic antagonist, 400 mg/kg/day) or L-arginine (260 mg/kg/day) from mid-pregnancy. The effect of the different treatments on systolic blood pressure (SBP), creatinine clearance (CCR), urine protein excretion (UP) and urinary nitrate excretion (UNO3, representing urine NO metabolite) were evaluated and the results compared with those found in normal pregnancy. Normal pregnant rats receiving similar treatment were used as controls. Results: In normal pregnant (P) rats, SBP values decreased from 94 ± 2 to 83 ± 3 mm Hg at the end of pregnancy (p < 0.01) and CCR augmented significantly. Drug treatment had no significant effect. In NAME-treated rats, at the same period, the SBP augmented from 92 ± 1 to 129 ± 1.8 mm Hg (p < 0.01). At the end of pregnancy, NAME rats had significantly lower CCR values and higher UP excretion when compared with P rats. UNO3 increased significantly in P and in P rats treated with methyldopa. As expected, in NAME rats UNO3 excretion was significantly reduced. Treatment with methyldopa normalized SBP, improved CCR and proteinuria and was associated with an increase in UNO3. Similar results were obtained with L-arginine treatment. Diltiazem lowered SBP significantly but had no effect on renal function or UNO3 and daltroban had no effect. Conclusion: The increased UNO3 found in NAME rats treated with methyldopa suggests that the vasoconstriction secondary to chronic NO inhibition may be partially related to an increased sympathetic activity. The efficient action of the sympathetic antagonist methyldopa may be due not only to its antihypertensive effects but also by its stimulating effect on NO synthesis leading also to an improvement of renal function.

Low Molecular Weight Heparin Reduces Proteinuria and Modulates Glomerular TNF-α Production in the Early Phase of Adriamycin Nephropathy

Background/Aim: Heparin has been shown to be renoprotective in a number of experimental nephropathies. The inflammatory component in the early phase of Adriamycin (ADR) induced nephropathy has been established. A microdose of low molecular weight heparin (Fragmin; F) has been noted to exert immunomodulatory effects independent of its anticoagulant activity. We assessed the effects of microdoses of F on daily proteinuria and glomerular production of tumor necrosis factor alpha (TNF-α) and prostaglandins 8 and 15 days after induction of ADR nephropathy. Methods: Following intravenous injection of ADR (7 mg/kg) to Wistar rats weighing 200 ± 20 g, F 20 µg/day/rat s.c. was administered for 8 and 15 days (groups F8 and F15). The respective control groups (C8 and C15) received normal saline subcutaneously. Proteinuria, serum albumin, and creatinine clearance were evaluated on days 8 and 15. The production of TNF-α and prostaglandins from glomerular supernatants was measured by radioimmunoassay on days 8 and 15. Results: F significantly reduced proteinuria (mg/day) on day 8: 13.6 ± 1.2 in F8 versus 40.3 ± 2.7 in C8 (p = 0.008). The glomerular production of TNF-α (pi/ml) was significantly lower on day 8 in rats treated with F: 356 ± 33 in F8 versus 764 ± 81 in C8 (p = 0.006). A decrease in the prostaglandin E2/thromboxane B2 ratio was noted in the F group between 8 and 15 days (1.1 in F8 vs. 0.9 in F15, p = 0.005) which principally reflects an increase of thromboxane B2. The antiproteinuric effect of F shown after 8 days was no longer present after 15 days (354 ± 91 mg/day in F15 vs. 499 ± 69 mg/day in C15, p = 0.33). The same trend was seen for the glomerular production of TNF-α. Light microscopy and immunohistochemistry for interstitial and glomerular macrophages were negative. Conclusion: The lowering effect of microdoses of F on the proteinuria seen during the early phase of ADR nephropathy may be mediated by a decreased production of glomerular TNF-α, supporting the anti-inflammatory action of low molecular weight heparin.

Effect of sodium and chloride depletion on urinary prostaglandin F2α excretion in potassium loaded rats

Previous studies have shown that the urinary excretion of prostaglandin (PG) F2 alpha is stimulated by potassium (K) loading. Because changes of sodium chloride (NaCl) intake also affect renal PG production, in this study we investigated the interaction between the effect of K and that of concomitant reduction of Na and Cl intake. The urinary excretion of PGF2 alpha and PGE2 was measured in 12 groups of female rats on normal, high or low K intake. Na and Cl intake were adjusted so that rats had normal intake (controls, C), were selectively Cl depleted (CD), selectively Na depleted (ND) or Na and Cl depleted (NCD). In rats with normal K intake, urinary PGF2 alpha was not modified by changes of Na or Cl intake, whereas PGE2 was increased in by Cl depletion (in both NCD or CD groups). Potassium chloride loading increased urinary PGF2 alpha and selective Na depletion (ND group) induced a further increase. On the other hand, PGF2 alpha was not stimulated when K load was associated with Cl depletion. Urine PGF2 alpha was directly correlated with plasma aldosterone and urinary kallikrein. Urinary PGE2 did not change with K-loading. The results suggest that PGF2 alpha participates in the renal adaptation to KCl-loading but not when K is accompanied by non-Cl anions.