Introduction. Transgenic rats with inducible angiotensin II (Ang II)-dependent hypertension (strain name: TGR[Cyp1a1-Ren2]) were generated by inserting the mouse Ren2 renin gene, fused to the cytochrome P450 1a1 (Cyp1a1) promoter, into the genome of the rat. The present study was performed to characterise the changes in plasma and kidney tissue Ang II levels and in renal haemodynamic function in Cyp1a1-Ren2 rats following induction of either slowly developing or malignant hypertension in these transgenic rats. Materials and Methods. Arterial blood pressure (BP) and renal haemodynamics and excretory function were measured in pentobarbital sodium-anaesthetised Cyp1a1-Ren2 rats fed a normal diet containing either a low dose (0.15%, w/w for 14-15 days) or high dose (0.3%, w/w for 11-12 days) of the aryl hydrocarbon indole-3-carbinol (I3C) to induce slowly developing and malignant hypertension, respectively. In parallel experiments, arterial blood samples and kidneys were harvested for measurement of Ang II levels by radioimmunoassay. Results. Dietary I3C increased plasma renin activity (PRA), plasma Ang II levels, and arterial BP in a dose-dependent manner. Induction of different fixed levels of renin gene expression and PRA produced hypertensive phenotypes of varying severity with rats developing either mild or malignant forms of hypertensive disease. Administration of I3C, at a dose of 0.15% (w/w), induced a slowly developing form of hypertension whereas administration of a higher dose (0.3%) induced a more rapidly developing hypertension and the clinical manifestations of malignant hypertension including severe weight loss. Both hypertensive phenotypes were characterised by reduced renal plasma flow, increased filtration fraction, elevated PRA, and increased plasma and intrarenal Ang II levels. These I3C-induced changes in renal haemodynamics, PRA and kidney Ang II levels were more pronounced in Cyp1a1-Ren2 rats with malignant hypertension. Chronic administration of the AT 1 -receptor antagonist,

Superoxide anion contributes to the pathogenesis of various forms of hypertension, but its role in the development of malignant hypertension remains unclear. The present study was performed to determine the influence of superoxide anion on blood pressure and renal hemodynamics in transgenic rats with inducible malignant hypertension [strain name: TGR(Cyp1a1Ren2)]. Malignant hypertension was induced in male Cyp1a1-Ren2 rats (n = 6) through dietary administration of the aryl hydrocarbon, indole-3-carbinol (0.3%) for 7-9 days. Mean arterial pressure (MAP) and renal hemodynamics were measured in pentobarbital sodium-anesthetized Cyp1a1-Ren2 rats before and during intravenous infusion of the superoxide dismutase mimetic tempol (100 mumol/h). Basal MAP and renal vascular resistance (RVR) were elevated in rats induced with indole-3-carbinol compared with noninduced rats (n = 5) (184 +/- 4 vs. 127 +/- 3 mmHg, P < 0.01, and 29 +/- 2 vs. 21 +/- 1 mmHg.ml(-1).min.g, P < 0.01, respectively). Hypertensive rats had elevated excretion of urinary 8-isoprostane compared with normotensive rats (41 +/- 4 vs. 13 +/- 6 pg.min(-1).g(-1), P < 0.01). There were no differences in renal plasma flow and glomerular filtration rate between groups. Systemic administration of tempol decreased MAP (184 +/- 4 to 151 +/- 4 mmHg, P < 0.01) and RVR (29 +/- 2 to 25 +/- 2 mmHg.ml(-1).min.g, P < 0.05) in hypertensive but not in normotensive Cyp1a1-Ren2 rats. In addition, tempol administration decreased urinary excretion of 8-isoprostane (41 +/- 4 to 25 +/- 4 pg.min(-1).g(-1), P < 0.05). Renal plasma flow and glomerular filtration rate remained unaltered during tempol administration in both groups. The administration of the nitric oxide synthase inhibitor nitro-l-arginine attenuated the decrease in MAP and RVR in response to tempol. These findings indicate that superoxide anion contributes to the elevated RVR and increased arterial blood pressure, by a mechanism that is at least in part nitric oxide dependent, in Cyp1a1-Ren2 rats with malignant hypertension.

Graciano ML, Mouton CR, Patterson ME, Seth DM, Mullins JJ, Mitchell KD. Renal vascular and tubulointerstitial inflammation and proliferation in Cyp1a1-Ren2 transgenic rats with inducible ANG II-dependent malignant hypertension. Am J Physiol Renal Physiol 292: F1858 -F1866, 2007. First published March 6, 2007;doi:10.1152/ajprenal.00469.2006.-Transgenic rats with inducible ANG II-dependent malignant hypertension [TGR(Cyp1a1Ren2)] were generated by inserting the mouse Ren2 renin gene into the genome of the rat. The present study was performed to assess renal morphological changes occurring during the development of ANG IIdependent malignant hypertension in these rats. Male Cyp1a1-Ren2 rats (n ϭ 10) were fed normal rat food containing indole-3-carbinol (I3C; 0.3%) for 10 days to induce malignant hypertension. Rats induced with I3C had higher mean arterial pressures (173 Ϯ 9 vs. 112 Ϯ 11 mmHg, P Ͻ 0.01) than noninduced normotensive rats (n ϭ 9). Glomerular damage was evaluated by determination of the glomerulosclerosis index (GSI) in tissue sections stained with periodic acid-Schiff. Kidneys of hypertensive rats had a higher GSI than normotensive rats (21.3 Ϯ 5.6 vs. 3.5 Ϯ 1.31 units). Quantitative analysis of macrophage ED-1-positive cells and proliferating cell nuclear antigen using immunohistochemistry demonstrated increased macrophage numbers in the renal interstitium (106.4 Ϯ 11.4 vs. 58.7 Ϯ 5.0 cells/mm 2 ) and increased proliferating cell number in cortical tubules (37.8 Ϯ 5.7 vs. 24.2 Ϯ 2.1 cells/mm 2 ), renal cortical vessels (2.2 Ϯ 0.5 vs. 0.13 Ϯ 0.07 cells/vessel), and the cortical interstitium (33.6 Ϯ 5.7 vs. 4.2 Ϯ 1.4 cells/mm 2 ) of hypertensive rat kidneys. These findings demonstrate that the renal pathological changes that occur during the development of malignant hypertension in Cyp1a1-Ren2 rats are characterized by inflammation and cellular proliferation in cortical vessels and tubulointerstitium. kidney; glomerulosclerosis; renal injury; immunohistochemistry; renin-angiotensin system; renal pathology; peptide hormones TRANSGENIC RATS WITH INDUCIBLE activation of extrarenal renin gene expression [TGR(Cyp1a1Ren2)] were generated using a renin transgene under the transcriptional control of the cytochrome P-450 (Cyp1a1) promoter (23). This transgenic rat line was created by inserting a mouse Ren2 renin gene, fused to an 11.5-kb fragment of the Cyp1a1 promoter, into the genome of the Fischer 344 rat (23). Cyp1a1, which catalyzes the oxidation of a wide range of endogenous lipophilic compounds and xenobiotics (7, 10, 43), is not constitutively expressed but is highly inducible on exposure to various aryl hydrocarbons such as indole-3-carbinol (I3C) (7,10,14,21,26,33,43). Induction of Cyp1a1 is mediated by the aryl hydrocarbon receptor, which is a basic helix-loop-helix-transcription factor that binds to specific DNA elements in the Cyp1a1 promoter (7, 13, 43). Rats transgenic for the Cyp1a1-Ren2 construct do not constitutively express the Ren2 renin gene. Rather, the Ren2 gene is expressed, primarily i...

The present study was performed to determine the effects of cyclooxygenase (COX)-1 and COX-2 inhibition on blood pressure and renal hemodynamics in transgenic rats with inducible malignant hypertension [strain name: TGR(Cyp1a1Ren2)]. Male Cyp1a1-Ren2 rats (n = 7) were fed a normal diet containing the aryl hydrocarbon, indole-3-carbinol (I3C; 0.3%), for 6-9 days to induce malignant hypertension. Mean arterial pressure (MAP) and renal hemodynamics were measured in pentobarbital sodium-anesthetized Cyp1a1-Ren2 rats during control conditions, following administration of the COX-2 inhibitor nimesulide (3 mg/kg iv), and following administration of the nonspecific COX inhibitor meclofenamate (5 mg/kg iv). Rats induced with I3C had higher MAP than noninduced rats (n = 7; 188 +/- 6 vs. 136 +/- 4 mmHg, P < 0.01). There was no difference in renal plasma flow (RPF) or glomerular filtration rate (GFR) between induced and noninduced rats. Nimesulide elicited a larger decrease in MAP in hypertensive rats (188 +/- 6 to 140 +/- 8 mmHg, P < 0.01) than in normotensive rats (136 +/- 4 to 113 +/- 8 mmHg, P < 0.01). Additionally, nimesulide decreased GFR (0.9 +/- 0.13 to 0.44 +/- 0.05 ml.min(-1).g(-1), P < 0.05) and RPF (2.79 +/- 0.27 to 1.35 +/- 0.14 ml.min(-1).g(-1), P < 0.05) in hypertensive rats but did not alter GFR or RPF in normotensive rats. Meclofenamate further decreased MAP in hypertensive rats (to 115 +/- 10 mmHg, P < 0.05) but did not decrease MAP in normotensive rats. Meclofenamate did not alter GFR or RPF in either group. These findings demonstrate that COX-1- and COX-2-derived prostanoids contribute importantly to the development of malignant hypertension in Cyp1a1-Ren2 transgenic rats. The data also indicate that COX-2-derived vasodilatory metabolites play an important role in the maintenance of RPF and GFR following induction of malignant hypertension in Cyp1a1-Ren2 transgenic rats.

No abstract

Neuronal nitric oxide synthase (nNOS)-derived NO and cyclooxygenase (COX)-2 metabolites exert pronounced renal vasodilator influences in transgenic rats [strain name: TGR(Cyp1a1Ren2] with ANG II-dependent malignant hypertension. This study was performed to determine if the renal vasodilator effects of COX-2 metabolites in hypertensive Cyp1a1-Ren2 rats are dependent on nNOS activity. Male Cyp1a1-Ren2 rats (n = 7) were fed a normal diet containing indole-3-carbinol (0.3%) for 7-9 days to induce malignant hypertension. Mean arterial pressure (MAP) and renal hemodynamics were measured in pentobarbital-anesthetized Cyp1a1-Ren2 rats during infusion of the nNOS inhibitor S-methyl-L-thiocitruline (L-SMTC, 1 mg/hr, iv) and following administration of the COX-2 inhibitor, nimesulide (3 mg/kg, iv). During infusion of L-SMTC, hypertensive rats had higher MAP (182 ± 2 vs. 153 ± 3 mm Hg, p < .01) than normotensive rats (n = 5). There were no differences in RPF (1.9 ± 0.2 vs. 2.0 ± 0.2 mL/min.g) and GFR (0.86 ± 0.07 vs. 1.00 ± 0.02 mL/min.g) between groups. Administration of nimesulide during continued L-SMTC infusion decreased MAP in both hypertensive and normotensive rats (182 ± 2 to 170 ± 3 mm Hg and 153 ± 3 to 140 ± 3 mm Hg, respectively, p < .01). Nimesulide also decreased RPF (1.9 ± 0.2 to 0.8 ± 0.1 mL/min.g, p < .01) and GFR (0.86 ± 0.07 to 0.40 ± 0.05 mL/min.g, p < .01) in hypertensive rats but did not alter RPF or GFR in normotensive rats. The present study confirms that COX-2 metabolites contribute to the elevated arterial pressure and exert pronounced renal vasodilator influences in Cyp1a1-Ren2 transgenic rats with inducible ANG II-dependent malignant hypertension. The data also demonstrate that the renal vasodilator effects of COX-2-derived prostanoids in hypertensive Cyp1a1-Ren2 transgenic rats are not dependent on nNOS activity.

No abstract