Enalapril and renal function in hypertensive rats transgenic for mouse renin gene

Specific MAP-kinase blockade protects against renal damage in homozygous TGR(mRen2)27 rats

Angiotensin II (AngII) plays an important role in renal damage by acting on hemodynamics, cell-growth, proliferation, and fibrosis, mainly by effects on the AngII type 1 (AT(1)) receptor. The AT(1) receptor activates several intracellular signaling molecules such as mitogen-activated protein kinases extracellular signal-regulated kinase (ERK) and p38, but their role in AngII-mediated renal damage is not well characterized. We therefore investigated whether pharmacologic blockade of ERK and p38 could prevent renal damage in high-renin homozygous transgenic rats (Ren2), with the effects of an AT(1) receptor antagonist (AT(1)-RA) as a reference. Seven-week-old homozygous Ren2 rats were treated with low-dose AT(1)-RA candesartan, ERK inhibitor tyrphostin, or p38 inhibitor SB239063 for 4 weeks. Untreated Ren2 and SD rats served as controls. Blood pressure was measured at 7 and 11 weeks. At 11 weeks, plasma renin activity (PRA) and serum aldosterone were determined, and the animals were killed. Kidney sections were scored for glomerular and interstitial smooth muscle actin and glomerular desmin expression as early markers for renal damage. Mesangial matrix expansion was determined as a marker for structural damage. PRA and aldosterone levels were elevated in untreated Ren2 rats in comparison to SD controls. AT(1)-RA further increased PRA but decreased aldosterone. All parameters of renal damage were elevated in untreated Ren2 rats. Blood pressure was not elevated at week 7 in Ren2 and not affected by either treatment. Mild signs of hypertensive damage were found in untreated Ren2 rats. All interventions significantly diminished damage to glomerular epithelium and interstitium. In addition, AT(1) receptor and p38 blockade reduced mesangial matrix expansion. In homozygous Ren2 rats, renal damage was ameliorated by a nonhypotensive dose of an AT(1)-RA and, similarly, by blockade of ERK or p38. This suggests that ERK and p38 are involved in AngII-mediated renal damage.

Cardiovascular risk, renal hypertensive damage, and effects of amlodipine treatment in transgenic TGR(mREN2)27 rats

Transgenic rats (TGRs) TGR(mREN2)27 are characterized by fulminant hypertension, an inverse circadian blood pressure rhythm, and severe hypertensive target organ damage. In the present study, we evaluated cardiovascular risk factors, renal function, and urinary protein loss in transgenic rats before and after treatment with the calcium channel blocker amlodipine. Amlodipine was injected intraperitoneally in a dose of 5 mg/kg/day, either once daily at 8.00 h or twice daily in divided doses at 8.00 and 20.00 h. Untreated TGRs and Sprague-Dawley rats served as hypertensive and normotensive controls, respectively. Before and after 5 weeks of treatment, rats were placed in metabolic cages for sampling of urine. Prior to treatment, urinary excretion rates of protein, albumin, and Ca2+ were significantly higher in TGRs than in Sprague-Dawley controls. Urinary excretion of protein and albumin was reduced by 5 weeks of amlodipine treatment, whereas the excretion of Ca2+ was not affected. The reductions in renal proteinuria and albuminuria by amlodipine treatment were significantly correlated with the treatment-induced decrease in blood pressure. These findings indicate that blood pressure itself is an important contributor to albumin loss by the kidney in renin-dependent hypertension of TGRs.

Urinary excretion of nitric oxide, cyclic GMP, and catecholamines during rest and activity period in transgenic hypertensive rats

Dysregulation of the system of nitric oxide (NO)-cyclic 3',5'-guanosine monophosphate (cGMP) might be involved in the development of hypertension in transgenic hypertensive TGR(mREN2)27 (TGR) rats. The present study was performed to determine possible differences in the day-night pattern and the urinary excretion rates of NO and cGMP in TGR rats in comparison to normotensive Sprague-Dawley (SPRD) controls. In addition, the urinary excretion of creatinine and catecholamines was measured in both rat strains. The day-night excretion patterns of NO, cGMP, catecholamines, and creatinine were preserved in TGR rats. Urinary excretion of NO was significantly decreased in TGR rats, whereas cGMP, the second messenger of NO, was elevated in the transgenic animals. Catecholamines and creatinine excretion rates did not differ between the strains. In conclusion, data suggest that a reduced NO synthesis could contribute to the increased blood pressure in the severely hypertensive rats. However, these data make it unlikely that the disturbances in the nitric oxide-cGMP system and the sympathetic nervous system are mainly responsible for the inverse circadian blood pressure rhythm in TGR rats.

Enhanced renal vascular responsiveness to angiotensin II in hypertensive ren-2 transgenic rats

The present study was performed to evaluate renal vascular responsiveness (RVR) to ANG II in hypertensive transgenic rats [TGR; strain TGR(mRen2)27] harboring the mouse ren-2 renin gene. Renal blood flow (RBF) responses to either intravenous or intrarenal arterial administration of ANG II were assessed in pentobarbital sodium-anesthetized female heterozygous TGR (9-12 wk old) and age-matched transgene-negative Hanover Sprague-Dawley rats (HanSD). Intravenous bolus injections of 15 and 30 ng ANG II elicited dose-dependent increases in mean arterial blood pressure (AP) and decreases in RBF in both TGR and HanSD. However, the magnitude of the increases in AP was greater in TGR than in HanSD (24 +/- 1 vs. 17 +/- 2 mmHg and 33 +/- 2 vs. 25 +/- 1 mmHg, respectively, P < 0.05 in both cases). Similarly, the magnitude of the decrease in RBF elicited by intravenous administration of 15 ng of ANG II was greater in TGR than HanSD (-62 +/- 3 vs. -52 +/- 5%, P < 0.05). Intrarenal arterial administration of 1.5 and 3 ng ANG II did not alter mean AP in either group but elicited larger decreases in RBF in TGR than in HanSD (-24 +/- 2 vs. -13 +/- 1% and -41 +/- 5 vs. -30 +/- 2%, respectively, P < 0.05 in both cases). In contrast, intrarenal arterial administration of norepinephrine (40 and 80 ng) elicited smaller decreases in RBF in TGR than in HanSD (-24 +/- 3 vs. -40 +/- 6% and -51 +/- 9 vs. -71 +/- 8%, respectively, P < 0.05 in both cases), indicating that TGR do not exhibit a generalized increase in RVR to endogenous vasoconstrictors. Furthermore, the enhanced RVR to ANG II does not appear to reflect an impaired RVR to endogenous vasodilator factors since intrarenal administration of bradykinin and acetylcholine elicited larger increases in RBF in TGR than in HanSD. The present findings indicate that hypertensive TGR exhibit exaggerated renal and peripheral vascular responses to ANG II, which likely contributes to an increased renal and peripheral vascular resistance and thereby to the hypertension in TGR.