FHH Rats Research Articles

Abstract 35: Gamma Adducin Dysfunction Leads To Cerebrovascular Distention, Blood Brain Barrier Leakage, And Cognitive Deficits In The Fawn-hooded Hypertensive Rats

We have previously identified an inactivating mutation of ADD3 in FHH rats which is associated with impaired myogenic reactivity of renal arterioles and podocyte function, and contributes to the development of CKD. We have found that SNPs in human ADD1 or ADD3 in the same region as Add3 in FHH rats are linked to reductions in brain volumes and impaired performance on cognitive tests in 4,286 elderly patients (67-90 years old) in the Atherosclerosis Risk in Communities Neurocognitive Study (ARIC-NCS), but the mechanisms of these pathologies are unclear. The present study examined cerebral hemodynamics and cognitive function in FHH versus FHH.1BN and FHH. Add3 rats that express the WT Add3 gene. The myogenic responses of the middle cerebral artery (MCA) and parenchymal arterioles (PA) were impaired in FHH rats. MCA diameter decreased by 15-20% in FHH.1BN (n = 27) and FHH. Add3 (n = 10) transgenic rats, but increased by 9 ± 3% in FHH rats (n = 15) when perfusion pressure was increased from 40 to 160 mmHg. PA diameter increased by 3.16 ± 2.79% in FHH (n = 5) rats versus a 19 ± 3% and 13 ± 2% decrease FHH. Add3 (n = 4) and FHH.1BN (n = 6), respectively, when pressure was increased from 10 to 40 mmHg. Autoregulation of surface and deep cortical blood flow was impaired in FHH rats and rose by 48 ± 3% (n = 22) and 41 ± 3% (n = 12), respectively, versus 32 ± 3% (n = 7) and 16 ± 5% (n = 6) in FHH. Add3 rats when MAP was increased from 100 to 160 mmHg. By using a fluorescent microscope to examine 60 μm brain sections, it was revealed that the outer diameters of PAs were distended in FHH in comparison to FHH.1BN and FHH. Add3 transgenic rats when systemic pressure was increased to 160 mmHg. Blood brain barrier leakage was also greater in FHH rats than in FHH.1BN and FHH. Add3 rats after acute elevations in pressure. FHH (n=16) rats took 40- 50% longer to navigate an eight-arm water maze than FHH. Add3 (n=11) and FHH.1BN (n=7) rats. These results indicate that variants that alter Add3 function promote cognitive dysfunction in FHH rats by altering cerebral hemodynamics and may play a similar role in cognitive deficits in elderly patients in the ARIC-NCS study. This study suggests that blood pressure should be strictly controlled in hypertensive patients identified with ADD3 variants to prevent dementia.

Abstract 145: Knockout of Gamma- Adducin Impairs Vascular Function in Renal Arterioles in Association With Htn-Induced Renal Injury

The FHH rat is a genetic model of hypertension that develops proteinuria, glomerulosclerosis, and chronic kidney disease. However, the genetic causes are unknown. We have previously identified an inactivating mutation of Add3 in FHH rats in association with reduced ADD3 expression and impaired myogenic reactivity of the renal arterioles. The vascular impairment and renal dysfunction were restored with knock-in of wild type (WT) Add3 in FHH rats. The present study examined whether knockout (KO) of Add3 in normal WT rats impairs the myogenic response of renal afferent arteriole (Af-art), interlobular arteriole (IA), arcuate arteriole (AA), renal blood flow (RBF) autoregulation, and if the reduction of expression of ADD3 promotes hypertension-induced renal dysfunction. Blood pressure was similar in 24-week old Add3 KO vs. WT rats, and after induction of 3 weeks of DOCA-salt-hypertension in these strains. Proteinuria was significantly higher in both normotensive and hypertensive Add3 KO compared with WT rats. KO of Add3 abolished the myogenic response of Af-art compared with WT rats. Similarly, the diameters of IA and AA increased 46 % (from 55.28 ± 2.95 um to 80.39 ± 0.41 um) and 25 % (from 92.57 ± 9.51 um to 115.49 ± 11.68 um) respectively in Add3 KO rats (n=4), while they remained unchanged in WT (n=5). Moreover, KO of Add3 abolished the RBF autoregulation compared with WT rats. These results indicate that KO of Add3 plays an important role to reduce the myogenic reactivity of renal arterioles and RBF autoregulation, and enhances renal damage after the onset of hypertension.

Down Regulation of Add3 in Astrocytes Disrupts the Actin Cytoskeleton in Association with Decreasing Small Molecule Uptake and May Contribute to Cognitive Deficits in FHH rats

We previously reported that the expression of Add3 is decreased in various tissues, including brain and cerebral vessels, and further decreases with age in FHH rats. More recently, we demonstrated that Add3 dysfunction contributes to cerebral vascular impairments in FHH rats, and they exhibit BBB leakage and neurodegeneration after the development of hypertension. In addition, Aβ protein expression in the brain in FHH rats is increased as early as 8 weeks of age. Reactive astrogliosis is a common finding in neurodegenerative diseases and activated astrocytes promote neurodegeneration. Moreover, astrocyte dysfunction affects Aβ clearance and Aβ accumulation is a characteristic biomarker of Alzheimer's disease. To further explore whether astrocytes contribute to neurodegeneration and cognitive impairments in FHH rats, we knocked down Add3 expression using Add3 Dicer‐substrate RNAi (DsiRNA) in human astrocytes and found that GFAP expression was markedly enhanced in comparison to scrambled siRNA treated cells. F‐actin distribution was significantly reduced in the Add3 DsiRNA treated cells (19.3 ± 6.7%, n = 6) when compared to the control cells (34.9 ± 3.0%, n = 6). In addition, the Add3 DsiRNA treated cells took up less fluorescence‐labeled dextran (10 kD) than the control cells suggesting the capability of uptake of small molecule, such as Aβ may be diminished. We found that DOCA/salt induced hypertensive FHH rats exhibit a reduction in neuronal density and size in the hippocampus. This was associated with loss of capillary density (22.7 ± 0.001% in FHH and 9.6 ± 0.014% in control rats, n = 7 and 9, respectively), and greater expression of GFAP positive astrocytes and loss of neurons in affected areas. Hypertensive FHH rats took 2.5 times longer to escape from an eight‐arm water maze as compared to control strains. These results suggest that down regulation of Add3 in astrocytes disrupts the actin cytoskeleton to induce reactive astrogliosis and may affect Aβ clearance, all of which may contribute to neurodegeneration and cognitive deficit associated with aging and hypertension in FHH rats.Support or Funding InformationThis study was supported by grants HL36279 (RJR) and DK104184 (RJR), AG050049 (FF), P20GM104357 (RJR, FF ) from the National Institutes of Health; 16GRNT31200036 (FF) from the American Heart Association. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Abstract 109: Gamma-adducin Effects on Microvascular Function- a Common Link of Hypertension Induced Chronic Kidney Disease and Cognitive Impairments

Chronic kidney disease (CKD) and cognitive impairments are common complications of hypertension. Increasing evidence suggests that the cognitive impairments associated with CKD may be related to microvascular dysfunction, however, the underlying mechanisms remain to be elucidated. FHH is a genetic model of hypertension-induced nephropathy. We found that the myogenic response and autoregulation of the renal and cerebral circulation is impaired in FHH rats, and was restored in a FHH.1 BN congenic strain in which a small region of Chr. 1 containing 15 genes, including Add3, from BN rats was transferred into the FHH background. The present study examined whether Add3 contributes to hypertension related CKD, and is associated with the development of cognitive impairments due to microvascular dysfunction. FHH rats exhibited impaired autoregulation of RBF in comparison with FHH.1 BN rats. Pgc estimated from the stop flow pressure increased by 20 mmHg in FHH rats when RPP was increased from 100 to 140 mmHg versus only 4 mmHg in FHH.1 BN . FHH rats developed severe renal injury, and proteinuria rose from 37 ± 2 to 260 ± 32 mg/day as they aged from 12 to 21 weeks, but rose by a significant lesser extent in FHH.1 BN and FHH.Add3 rats. Glomerular injury scores were 3.31 ± 0.01, 2.54 ± 0.01 and 2.50 ± 0.03, and areas of fibrosis in renal cortex were 23.57 ± 1.04%, 8.28 ± 0.33 and 4.71 ± 0.3 in DOCA/salt induced hypertensive FHH, FHH.1 BN and FHH.Add3 rats, respectively. CBF rose by 99 ± 7%, 64 ± 5% and 42 ± 4% in FHH, FHH.1 BN and FHH.Add3 rats, respectively, when MAP was increased from 100 to 190 mmHg, demonstrating impaired autoregulation of CBF in FHH rats was partially rescued with the replacement of wildtype Add3. BBB leakage was greater in FHH rats than in FHH.1 BN and FHH.Add3 rats, and hypertensive FHH rats exhibited marked neurodegeneration and vascular remodeling of the neocortex and hippocampus. The hypertensive FHH rats took 2.5 times longer time to escape from an eight-arm water maze in comparison to FHH.1 BN rats suggesting cognitive deficit. These results indicate that Add3 may play a role in the development of hypertension related CKD and cognitive impairments in FHH rats associated with microvascular dysfunction.

Abstract P120: Down Regulation of Add3 in Astrocytes Induces Pro-inflammatory and Fibrotic Factors and May Contribute to Alzheimer’S-related Dementias

We genetically mapped a mutation in Add3 in FHH rats that decreases Add3 expression in various tissues, including brain and cerebral vessels, and further decreases with age in comparison with FHH.1 BN congenic rats in which Chr. 1 from BN rats containing 15 genes, including Add3, was transferred onto FHH genetic background. More recently, we demonstrated that Add3 dysfunction contributes to cerebral vascular impairments in FHH rats, and they exhibit BBB leakage and neurodegeneration after the development of hypertension. In addition, Aβ protein expression in the brain in FHH rats is increased as early as 8 weeks of age. Reactive astrogliosis is a common finding in neurodegenerative diseases and activated astrocytes promote neurodegeneration. Moreover, astrocyte dysfunction affects Aβ clearance and Aβ accumulation is a well-defined feature of Alzheimer’s disease. To further explore whether astrocytes contribute to neurodegeneration and cognitive impairments in FHH rats, we knocked down Add3 expression using Add3 Dicer-substrate RNAi (DsiRNA) in human astrocytes and found that GFAP and IL-6 expression was markedly enhanced in comparison to scramble siRNA treated cells using a q-PCR array. Moreover, the expression of TGF-β2 and TGF-β3 was elevated by 2.0 ± 2.9 and 1.8 ± 1.8 folds, respectively, in Add3 DsiRNA treated astrocytes. In addition, the actin cytoskeleton was disrupted in Add3 DsiRNA treated astrocytes. We found that FHH rats exhibit a reduction in neuronal density and neuronal size in the hippocampus following the induction of hypertension with DOCA/salt. This was associated with loss of capillary density (22.7 ± 0.001% in FHH and 9.6 ± 0.014% in FHH.1 BN , n = 7 and 9, respectively) and greater expression of GFAP positive astrocytes and loss of neurons in affected areas. Hypertensive FHH rats took 2.5 times longer to escape from an eight-arm water maze as compared to control strains. These results suggest that down regulation of Add3 in astrocytes disrupts the actin cytoskeleton to induce reactive astrogliosis and release of pro-inflammatory and fibrotic factors, which promotes inflammation and disrupts Aβ uptake, all of which may contribute to neurodegeneration and cognitive deficit associated with aging and hypertension in FHH rats.

Abstract P434: Role of Dusp5 in Hypertension Induced Chronic Renal Disease

We recently identified 4 single nucleotide polymorphisms in Dusp5 in FHH as compared with Brown-Norway (BN) rats, two of which alter CpG sites and another one causes G155R mutation. We then created a Dusp5 knockout (KO) rat in the FHH.1 BN genetic background, in which a small region in Chr. 1 of BN rats containing 15 genes, including Dusp5 into the FHH rats. We found that knockout of Dusp5 enhances the myogenic response and autoregulation of cerebral circulation. In the present study, we evaluated whether Dusp5 also plays a role in the regulation renal function. The expression of Dusp5 was lower in FHH. 1 BN . Dusp5 KO rats in comparison to the FHH.1 BN rats. The levels of p-PKC and p-ERK1/2 were elevated in Dusp5 KO vs. FHH.1 BN rats. The blood pressure and urinary protein excretion was similar in FHH. 1 BN . Dusp5 KO (n = 43) and FHH.1 BN rats (n = 30) when they were at 12-week of age (114 ± 2 vs. 115 ± 1 mmHg and 32 ± 2 vs. 29 ± 3 mg/day). The autoregulation of RBF was similar in FHH.1 BN (n=22) and Dusp5 KO (n = 9) rats in response to elevation of MAP from 100 to 140 mmHg, but was impaired in FHH rats (n=21) that increased by 37.3 ± 2.3% when they were at 12-week of age. In response to an elevation in pressure from 60 to 120 mm Hg, the renal afferent arterioles constricted by 29 ± 2% and 11 ± 1%, respectively in Dusp5 KO (n = 6) in comparison to FHH.1 BN rats (n = 17). Blood pressure was similar in Dusp5 KO (n = 11) vs. FHH.1 BN rats (n = 14) after 3-week DOCA-salt treatment (169 ± 5 vs. 177 ± 5 mmHg). However, proteinuria was significantly reduced in Dusp5 KO rats (258 ± 22 mg/day, n = 12) in comparison to FHH.1 BN rats (338 ± 30 mg/day, n = 12). The renal injury induced by DOCA-salt was markedly reduced in Dusp5 KO vs. FHH.1 BN rats as the glomerular injury scores were 2.49 ± 0.03 vs. 2.54 ± 0.01; the areas of renal fibrosis were 5.5 ± 0.5% vs. 8.3 ± 0.3%; the areas of renal protein casts were 0.5 ± 0.2% vs. 2.4 ± 1.0% and renal arteriolar media-to-lumen ratios were 0.64 ± 0.03 vs. 0.81 ± 0.04, respectively. These results indicate that KO of Dusp5 enhances renal vascular function to protect against DOCA-salt hypertension induced chronic renal injury via activation of PKC/ERK signaling pathway. In conclusion, an activating mutation in Dusp5 may contribute to the impaired myogenic response and promote the development of chronic renal injury in FHH rats.

Abstract P124: Role of Add3 Dysfunction in Renal Epithelial Cells in the Development of Renal Injury in Fhh Rats

The Fawn Hooded Hypertensive Rat (FHH) is a genetic model of hypertension, in which Add3 has been identified as a candidate gene for renal injury but the mechanism is unknown. The present study examined the effects of knockdown of Add3 on rat renal epithelial (NRK) cells which are the model system for podocytes and proximal tubular cells. Knockdown of the expression of Add3 using a 27-mer Dicer-substrate RNAi (DsiRNA) decreased cell viability using an MTS assay by 50% in comparison to cells treated with vehicle or scrambled DSiRNA (Add3DsiRNA, OD 0.5±0.1; untreated cells 0.9±0.1; NC-1 0.9±0.1; n=8, P<0.001). F-actin immunostaining revealed that Add3 DSiRNA markedly disrupted the cytoskeleton, and the F-actin staining intensity/cell ratio was significantly reduced (untreated 543±47, n=552 cells; NC-1 592±39, n=566 cells; Add3DsiRNA 430±58, n=385 cells, P<0.05). The maximum mitochondrial respiratory rate was reduced in Add3 DsiRNA treated cells (untreated 444±42; NC-1 414±32; Add3 DsiRNA 275±16 pmole/min/μg, P<0.01). Proton leak was higher (untreated 42±3; NC-1 40±4; Add3 DsiRNA 63±5 pmole/min/μg, P<0.002) and oxygen consumption coupled to ATP production was decreased in Add3 DsiRNA treated cells (untreated 229±12, n=9; NC-1 200±12, n=8; Add3 DsiRNA 146±11 pmole/min/μg, n=9, P<0.001). Spare respiratory capacity, an index of cell fitness, was reduced by knockdown of Add3 (untreated 154±42, n=9: NC-1 143±32, n=8; Add3DsiRNA 33±16 pmole/min/μg, n=9, P<0.001). Non-mitochondrial oxygen consumption rate (OCR/μg protein) increased in cells treated with Add3 DsiRNA (untreated 57±7; NC-1 80±11; Add3DsiRNA 116±15 pmole/min/μg, P<0.01) suggesting a possible metabolic switch to glycolytic oxygen consumption. In conclusion, knockdown of Add3 in NRK cells disrupts the actin cytoskeleton, promotes mitochondrial dysfunction and decreases cell viability. Loss of Add3 function may contribute to proteinuria in FHH rats by altering the cytoskeleton and promoting effacement and loss of podocytes and the reuptake of filtered protein in the proximal tubule.

Impaired myogenic response of MCA elevates transmission of pressure to penetrating arterioles and contributes to cerebral vascular disease in aging hypertensive FHH rats

We recently identified a K572Q mutation in Add3 in FHH rats. The present study examined whether it contributes to cerebral vascular dysfunction in aging and after the development of hypertension. The expression of Add3 is lower in FHH than in FHH.1BN rats. The inner diameter of MCA decreased by 80 ± 2 % and 71 ± 4% in FHH.1BN and FHH.Add3 transgenic rats, respectively, when perfusion pressure was increased from 40 to 140 mmHg. The pressure in terminal pial arteries was greatly increased from 37 ± 1 to 63 ± 4 mmHg in FHH rats when MAP was increased from 100 to 160 mmHg but was unchanged (34 ± 1 to 36 ± 1 mmHg) in FHH.1BN rats. The inner diameters of capillaries in the deep cortex were markedly larger (8 ± 2 vs. 22 ± 1 μm) and capillary density was reduced (15 ± 0.4% vs. 8 ± 2%) in FHH than in FHH.1BN rats. The expression of phosphorylated‐ERK1/2 and phosphorylated‐PKC was reduced in the brain of FHH than FHH.1BN rats. CBF rose by 99 ± 7%, 64 ± 5% and 42 ± 4% in FHH, FHH.1BN and FHH.Add3 rats, respectively, when MAP was increased from 100 to 190 mmHg, demonstrating that the impaired autoregulation of CBF in FHH rats was rescued by introduction of wildtype Add3. BBB leakage was greater in FHH rats than FHH.1BN and FHH.Add3 rats after induction of DOCA/salt hypertension. Hypertensive FHH rats exhibited marked neurodegeneration and vascular remodeling of the neocortex and hippocampus with a 33% reduction in the density and size of neurons relative to FHH.1BN and FHH.Add3 rats. Gap junctions between endothelial cells were larger in hypertensive FHH rats with neuronal, mitochondrial and myelin degeneration in the vacuolated area near leaky capillaries. The hypertensive FHH rats took 2.5 times longer to escape from an eight‐arm water maze than hypertensive FHH.1BN rats suggesting spatial learning and memory dysfunction. These findings suggest that the K572Q mutation in FHH rats decreases the expression and activity of Add3 which is involved in phosphorylation of PKC and ERK1/2. This contributes to the impaired myogenic response and autoregulation of CBF, therefore elevating the transmission of pressure in penetrating arterioles that ultimately promotes loss of cerebral capillaries, BBB leakage and neurodegeneration, which may contribute to vascular cognitive impairments with hypertension and age.Support or Funding InformationThis study was supported by grants HL36279 and DK104184 (RJR) from the National Institutes of Health.

Abstract MP14: A K572Q Mutation in Gamma-adducin Is Responsible for the Impaired Myogenic Response and Autoregulation of Renal and Cerebral Blood Flow in FHH Rats

The FHH rat is a genetic model of hypertension induced CKD, but the genes and pathways involved are unknown. We recently reported that the myogenic response of the renal and cerebral arteries is impaired in FHH rats and it was restored in a FHH.1BN congenic strain in which a small region of Chr. 1 containing 15 genes, including gamma-Adducin (Add3), from BN rats was transferred into the FHH background. We further identified a K572Q mutation in Add3 in FHH versus FHH.1BN rat. The present study examined the contribution of Add3 to the impaired myogenic reactivity using Add3 transgenic and KO rats. The diameter of the middle cerebral artery (MCA) decreased by 20-30% in SD, FHH.1BN and FHH.Add3 transgenic rats when perfusion pressure was increased from 40 to 140 mmHg. In contrast, the MCA of FHH and SD.Add3 knockout rats did not constrict. The myogenic response of the MCA is also impaired in MNS rats that share the same mutation in Add3 as in FHH rat and this phenotype was complemented in a F1 cross of FHH and MNS strain. Autoregulation of CBF was impaired in FHH rats and rose by 99 ± 7% when MAP was increased from 100 to 190 mmHg and was restored in FHH.Add3 and FHH.1BN rats. Similarly, the diameter of Af-art of FHH, MNS and a F1 cross of FHH and MNS rat increased in response to increase in perfusion pressure but decreased in FHH.1BN rats that have wild type Add3. FHH rats exhibited impaired autoregulation of RBF in comparison with FHH.1BN rats. Pgc estimated from the stopflow pressure increased by 20 mmHg in FHH rats when RPP was increased from 100 to 140 mmHg versus only 4 mmHg in the congenic strain. FHH rats developed severe renal injury and proteinuria rose from 37 ± 2 to 260 ± 32 mg/day as they aged from 12 to 21 weeks, but rose by a significant lesser extent in FHH.1BN and FHH.Add3 rats. BK current in VSMC isolated from the MCA was 5-fold higher in FHH vs. FHH.1BN rats. Administration of IBTX normalized the elevated BK channel current and restored the myogenic response in FHH rats but it had little effect in FHH.1BN. These results indicate that the K572Q mutation in Add3 plays a causal role in the impaired myogenic response and autoregulation of renal and cerebral circulation in FHH rats and may contribute to the development of renal and cerebral end organ damage with aging and after the onset of hypertension.

The Role of Nitric Oxide System in The Regulation of Renal Function During Prehypertensive and Hypertensive Period in Fawn‐Hooded Rat

Objective: Fawn-Hooded (FH) rat strain represents unique model of hypertension with renal failure. Normotensive FHL rats serve as a control whereas FHH develop early hypertension and exhibit increased susceptibility to renal disease due to impaired autoregulatory efficiency of the kidney. Aim of this study was to examine the influence of nitric oxide (NO) system in FHL and FHH rats in prehypertensive and hypertensive period. Design and method: 3 and 9 months old FHH and FHL rats were anesthetized, NO synthase inhibitor (L-NAME) were infused via jugular vein in dose 50 μg/kg of body weight and mean arterial pressure (MAP), renal blood flow (RBF), glomerular filtration rate (GFR), urine flow (UF) and sodium excretion responses were measured. Results: FHH rats exhibited significantly higher basal MAP compare to FHL in 3 month (123 ± 2,9 vs. 101 ± 2,5 mmHg) and also in 9 month (141 ± 2,1 vs. 102 ± 2,4 mmHg). Young FHH had higher basal RBF than FHL (6,5 ± 0,2 vs. 5,4 ± 0,5 ml/min/g) although older FHH rats had slightly lower RBF compare to FHL (3,7 ± 0,5 vs. 4,9 ± 0,5 ml/min/g) and also GFR (0,47 ± 0,07 vs. 0,66 ± 0,09 ml/min/g). L-NAME administration led to similar responses in both ages in MAP, RBF and GFR but hypertensive FHH had significantly lower increase in UF (from 3,7 ± 0,4 to 13,6 ± 2,5 µl/min/g) compare to FHL (from 4,4 ± 0,8 to 29,7 ± 2,6 µl/min/g) and also in sodium excretion (from 0,19 ± 0,07 to 1,57 ± 0,54 µmol/min/g) than in FHL (from 0,14 ± 0,08 to 3,77 ± 0,57 µmol/min/g). Conclusions: This study indicates that FHH rats with developed hypertension exhibit impaired renal hemodynamics and tubular function that may be caused by relative NO deficiency in the kidney.

Abstract 485: Enhanced Large Conductance Ca+2 -sensitive K+ Channels (bk) Activity Impairs the Myogenic Response in the Cerebral Vasculature of Fawn Hooded Hypertensive (fhh) Rat

Our recent studies have revealed that the myogenic response in cerebral arteries and autoregulation of cerebral blood flow is impaired in FHH and that transfer of a 2.4 Mb region of chromosome 1 from BN into FHH.1 BN congenic strain restores these responses. The present study examined the role of large conductance calcium activated potassium (BK) channel in altering the myogenic response in FHH rats. Whole-cell patch-clamp of cerebral vascular smooth muscle cells (VSMC) revealed a 4.6 fold increase in outward potassium (K) channel current densities (pA/pF) in FHH rats compared to FHH.1 BN congenic strain. Iberiotoxin (IBTX -a selective BK channel inhibitor) sensitive current densities are significantly greater in FHH rats compared with the FHH.1 BN congenic strain (FHH rats: +40mV; pre IBTX 43.1 ± 7.2, after IBTX 11.8 ± 2.2 pA/pF versus pre IBTX 5.6 ± 1 pA/pF and after IBTX 4.1 ± 0.6 pA/pF in the FHH.1 BN congenic strain). In excised patches, the BK channel exhibited similar single-channel slope conductance for FHH and the FHH.1 BN rats (208.9 pS versus 208.7 pS). However, the open channel probability (NP o ) was ~10 fold higher in FHH rats than in FHH.1 BN rats (1μM free (Ca +2 ) i : +40mV: FHH; 0.8 ± 0.04 versus 0.08 ± 0.004 in FHH.1 BN rats). Voltage and Ca 2+ sensitivity of the BK channel is similar in cerebral VSMC isolated from FHH and FHH.1 BN rats. Middle cerebral arterioles (MCA) isolated from FHH rats increased in diameter from 142 ± 16 to 157 ± 19 μm when pressure was increased from 40 to 140 mmHg. In contrast, the diameter of the MCA decreased by 49% in the FHH.1 BN congenic strain from 127 ± 16 to 65 ± 13 μm. Pharmacological block of BK channel by IBTX (100nM) restored myogenic response in FHH rats but had no effect in FHH.1 BN rats. These results indicate that the impaired myogenic response of the cerebral vessels in FHH rats is mediated via a gene and mechanism that enhances BK channel activity.

Survival time after hemorrhage (STaH) in inbred rats with known blood volumes

Eight‐fold differences in STaH were detected among 15 inbred rat strains (Klemcke et al., Shock 29:748, 2008) suggesting genetic effects on STaH. In that study, blood volumes (BV) for all strains were assumed to be 5.83 % of body weight and 55% of that BV was removed. We also showed that differences in STaH might reflect strain‐dependent differences in BV (Klemcke et al., FASEB J 23: 801.1, 2009). To address this hypothesis, each rat of 5 inbred rat strains was hemorrhaged based on its own BV measured using Evans Blue dye 24 hr prior to hemorrhage and its STaH determination. BV varied (P <0.01) among Brown Norway (BN/Mcwi; n = 14; 7.43 ± .10 ml/100 g body weight, mean ± SEM), Salt Sensitive (S; n = 10; 7.08 ± .15), Fawn Hooded Hypertensive (FHH; n=10; 6.74 ± .08), Lewis (LEW; n=10; 6.74 ± .08), and DA (n=10; 6.74 ± .08) rat strains. With equal hemorrhages (47.1 ± .05 % of measured BV), STaH did not differ among rat strains (155 ± 12 min; P = 0.95). When considering both studies it is apparent that: 1) Strain‐related differences in BV contributed to differences in STaH in our 1st study; 2) In FHH rats 1.3% more of total BV was removed in the current study, yet they survived 1.5 hr longer; and 3) In LEW rats identical BV were removed in both studies, yet currently LEW rats survived 1 hr longer. Such observations suggest that Evans Blue dye and/or blood sampling for BV determinations might be preconditioning stimuli that improve STaH in some rat strains.

Renal vascular dysfunction precedes the development of renal damage in the hypertensive Fawn-Hooded rat

It is unknown whether generalized vascular dysfunction precedes the development of kidney disease. Therefore, we studied myogenic constriction and endothelium-mediated dilatory responses in two inbred Fawn-Hooded (FH) rat strains, one of which spontaneously develops hypertension, proteinuria, and glomerulosclerosis (FHH), whereas the other (FHL) does not. Small renal, mesenteric resistance arteries and thoracic aorta isolated from FH rats before (7 wk old) and after the development of mild proteinuria (12 wks old) were mounted in perfused and isometric set-ups, respectively. Myogenic response, endothelium-dependent relaxation, and the contribution of endothelium-mediated dilatory compounds were studied using their respective inhibitors. Myogenic reactivity was assessed constructing pressure-diameter curves in the presence and absence of calcium. At the age of 7 wk, renal arteries isolated from kidneys of FHH rats developed significantly lower myogenic tone compared with FHL, most likely because of excessive cyclo-oxygenase 1-mediated production of constrictive prostaglandins. Consequently, young FHH demonstrated reduced maximal myogenic tone (22 +/- 4.8 vs. 10.8 +/- 2.0%, P = 0.03) and the peak myogenic index (-6.9 +/- 4.8 vs. 0.6 +/- 0.8%/mmHg, P = 0.07 for FHL vs. FHH, respectively). Active myogenic curves obtained in mesenteric arteries isolated from 7-wk-old rats did not differ between either strain, demonstrating a similar level of systemic myogenic tone in FHL and FHH rats. Therefore, before any renal end-organ damage is present, myogenic response seems selectively impaired in renal vasculature of FHH rats. Aortic reactivity did not differ between FHL and FHH at the time points studied. The present study shows that vascular dysfunction in both small renal and systemic arteries precedes renal end-organ damage in a spontaneous model of hypertension-associated renal damage. These early vascular changes might be potentially involved in the increased susceptibility of FHH rats to renal injury.

Irbesartan (Irb) Treatment Ameliorates Renal Damage in High Protein Fed FHH Rats: Role of L‐Arginine (arg) Pathways

The FHH rat is a model of spontaneous glomerulosclerosis, resulting from five renal failure genes (Rf 1‐5), exacerbated by high protein intake. We studied the effects of AT‐1 blockade, via Irb, on arg synthesis and utilization. Arg is synthesized by renal argininosuccinate synthase/lyase (ASS/ASL) and then either consumed within the kidney by arginase II or NOS, or released into the circulation. Arg competes for NOS with ADMA, which is degraded by dimethylarginine dimethylaminohydrolase (DDAH) 1/2. Male FHH rats (6wks old) were put on a 40% casein diet, with (HP+Irb; n=10) or without (HP; n=10) Irb treatment, for 13 wks. Data are summarized in Table (* p<0.05, ** p<0.01, *** p<0.001). HP+Irb rats had reduced proteinuria (UpV mg/24h/100gBW), blood pressure (BP, mmHg), kidney weight (KW, g), glomerulosclerosis index (GSI), and creatinine clearance (CCr, ml/min/100gBW). HP+Irb rats had reduced expression of eNOS (70%) and DDAH2 (65%), higher DDAH1 (120%) and nNOS (>500%) vs. HP. There was no change in the expression of ASS and ASL and Irb reduced arginase II (35%), which allow more arg for NO synthesis. Increased arginase II, and decreased nNOS and DDAH1 expression in HP rats are potential mechanisms for renal injury. These data suggest that Irb may improve renal outcome both by increasing arg supply to the kidney by lowering arginase, and by increasing nNOS expression.

Urinary clusterin levels in the rat correlate with the severity of tubular damage and may help to differentiate between glomerular and tubular injuries.

Clusterin is a secreted glycoprotein that is synthesized after several types of tubular injury. We therefore wondered whether the urinary excretion of clusterin could serve as a parameter to determine the severity of tubular damage. Using an affinity-purified rabbit antiserum raised against recombinant clusterin, we established an enzyme-linked immunosorbent assay to measure the urinary excretion of clusterin after bilateral renal ischemia, in the (cy/ +) rat model of autosomal-dominant polycystic kidney disease and in the FHH rat model of focal segmental glomerulosclerosis. After bilateral renal ischemia, the urinary excretion of clusterin paralleled the excretion of total protein and albumin and correlated with the extent of tubular damage. Male (cy/ +) rats, but not female (cy/ +) rats, excreted more clusterin than age-matched (+/ +) rats, a finding consistent with the more rapid course of the disease in males. FHH rats presented with pronounced proteinuria and albuminuria but did not excrete increased levels of clusterin. Urinary clusterin levels could therefore serve as a valuable marker for the severity of tubular damage. Furthermore, clusterin may also help to differentiate between tubular and glomerular forms of proteinuria.

Ventilatory phenotypes among four strains of adult rats.

Our purpose in this study was to identify different ventilatory phenotypes among four different strains of rats. We examined 114 rats from three in-house, inbred strains and one outbred strain: Brown Norway (BN; n = 26), Dahl salt-sensitive (n = 24), Fawn-hooded Hypertensive (FHH: n = 27), and outbred Sprague-Dawley rats (SD; n = 37). We measured eupneic (room air) breathing and the ventilatory responses to hypoxia (12% O(2)-88% N(2)), hypercapnia (7% CO(2)), and two levels of submaximal exercise. Primary strain differences were between BN and the other strains. BN rats had a relatively attenuated ventilatory response to CO(2) (P < 0.001), an accentuated ventilatory response to exercise (P < 0.05), and an accentuated ventilatory roll-off during hypoxia (P < 0.05). Ventilation during hypoxia was lower than other strains, but hyperventilation during hypoxia was equal to the other strains (P > 0.05), indicating that the metabolic rate during hypoxia decreased more in BN rats than in other strains. Another strain difference was in the frequency and timing components of augmented breaths, where FHH rats frequently differed from the other strains, and the BN rats had the longest expiratory time of the augmented breaths (probably secondary to the blunted CO(2) sensitivity). These strain differences not only provide insight into physiological mechanisms but also indicate traits (such as CO(2) sensitivity) that are genetically regulated. Finally, the data establish a foundation for physiological genomic studies aimed at elucidating the genetics of these ventilatory control mechanisms.

Transfer of the Rf-1 region from FHH onto the ACI background increases susceptibility to renal impairment.

The genetically hypertensive fawn-hooded (FHH/Eur) rat is characterized by the early presence of systolic and glomerular hypertension, progressive proteinuria (UPV), and albuminuria (UAV), and focal glomerulosclerosis, resulting in premature death from renal failure. Previous studies showed that at least five genetic loci (Rf-1 to Rf-5) were linked to the development of renal impairment. Of these five, Rf-1 appears to play a major role. To study the impact of Rf-1 in the absence of the other loci, we transferred the Rf-1 region of chromosome 1, between the markers D1Mit34 and D1Rat156, Rf-1B for short, onto the genomic background of the normotensive August x Copenhagen Irish (ACI) rat. In this congenic strain, named ACI.FHH-D1Mit34/Rat156 or ACI.FHH-Rf1B, we challenged the renal hemodynamic function of these animals by studying the effects of unilateral nephrectomy (UNX) alone, or combined with N(G)-nitro-L-arginine methyl ester (L-NAME)-induced hypertension. Following UNX, the congenic strain developed significantly more UPV and UAV than the ACI progenitor. The differences were even more pronounced when UNX was combined with an L-NAME-induced rise in systolic blood pressure to about 150 mmHg, i.e., the level of hypertension present in the parental FHH strain. These findings indicate that the Rf-1B region of the FHH rat contains at least one gene affecting the susceptibility to progressive renal failure, especially in the presence of an increase in blood pressure.

ACE inhibition delays development of terminal renal failure in the presence of severe albuminuria

The hypertensive fawn-hooded (FHH) rat develops progressive albuminuria (UalbV) and focal glomerulosclerosis (FGS). Early-onset angiotensin-converting enzyme inhibition (ACE-i) completely prevented the development of hypertension, UalbV, and FGS. ACE-i was still effective when the start of treatment was delayed, albeit less than early-onset treatment. In this study, we examined whether more advanced renal damage reduces the efficacy of ACE-i, and, if so, which factors dampen the efficacy. ACE-i was started in 36-week-old FHH rats, and follow-up consisted of regular assessment of systolic blood pressure (SBP) and UalbV. Untreated rats, matched for age, SBP, and UalbV, served as controls. In separate groups, untreated or treated with ACE-i from either week 7 or week 36, glomerular hemodynamics and FGS were determined at week 40. ACE-i normalized SBP and markedly reduced UalbV. The initial UalbV response to ACE-i was inversely correlated with pretreatment UalbV, but despite control of SBP, UalbV rose again. Eventually, rats died of terminal renal failure. Life expectancy was significantly increased in treated rats. In both untreated and treated rats, there was a significant inverse correlation between baseline UalbV and survival time. However, the gain in survival time decreased when pretreatment UalbV was higher. Late-onset ACE-i reduced glomerular capillary pressure to the same extent as early-onset ACE-i. There was a significant linear correlation between FGS and UalbV. We conclude that in FHH rats with advanced renal damage, ACE-i slows down the progression to terminal renal failure. The outcome is an increased survival time that is inversely correlated with baseline UalbV.

Tubuloglomerular feedback and prolonged ACE-inhibitor treatment in the hypertensive fawn-hooded rat.

The spontaneously hypertensive fawn-hooded (FHH) rat develops severe glomerulosclerosis with ageing. The afferent arteriolar resistance is low, resulting in a strongly elevated glomerular capillary pressure (P(GC)). Afferent arteriolar resistance is under the control of the tubuloglomerular feedback (TGF) system, and we studied whether young FHH rats, i.e. at a stage when only mild glomerulosclerosis was present, have diminished TGF responsiveness. Maximum TGF-mediated decreases in stop-flow pressure in response to late proximal perfusion with artificial tubular fluid were 9.0 +/- 1.0 mmHg, a value not different or even slightly lower than observed in normal rats. P(GC) was 59.9 +/- 1.2 mmHg and the estimated P(GC) at half-maximal activation of the TGF system (operating P(GC)) was 54.5 +/- 0.8 mmHg at 11 weeks of age (n = 11), a value higher than observed in normal rats. The second question of the present study concerns the effect of chronic angiotensin-I-converting enzyme inhibitor (ACE-i) administration on P(GC). ACE-i, by reducing angiotensin II (Ang II) availability, diminishes TGF responsiveness, which would offset the beneficial effect on P(GC) under normal flow conditions to the macula densa. Maximum TGF responses were 8.9 +/- 1.0 and 17.5 +/- 1.5 mmHg in 11- and 26-week-old rats that had been treated with the ACE-i lisinopril in the drinking water started when the animals were 7 weeks of age. P(GC) was 44.3 +/- 1.2 (n = 9) and operating P(GC) was 40.1 +/- 1.6 mmHg (n = 9) at 11, values significantly lower than in untreated rats. Values remained lower in the 26-week-old treated animals and were 40.9 +/- 0.8 and 32.6 +/- 1.1 mmHg. (1) the TGF system in this model of spontaneous hypertension and glomerulosclerosis is intact, despite the fact that the FHH rat has a characteristically low afferent arteriolar resistance as compared to other hypertensive rats; (2) the rat displays a normal or even enhanced function of the TGF system following prolonged administration of the ACE-i lisinopril. The latter finding indicates that the reduction of P(GC) achieved by the ACE-i is not offset by a concomitant attenuation of TGF function.

Genetic differences define severity of renal damage after L-NAME-induced hypertension in rats.

Genetic factors are important in determining the susceptibility to renal damage. In a backcross of the hypertensive and proteinuric fawn-hooded Erasmus University Rotterdam (FHH/EUR) rat with the normotensive, nonproteinuric August Copenhagen Irish (ACI/EUR) rat, two genes (denoted Rf-1 and Rf-2) were genetically mapped for parameters of functional and structural renal damage. The aim of the present study was to investigate the susceptibility to functional and structural renal damage in heterozygous (FHH X ACI) F1 rats compared with the parental FHH and ACI strains at similar levels of systolic BP (SBP). BP elevation was induced by chronic treatment with NG-nitro-L-arginine methyl ester (L-NAME) in either a low dose (LD, 75 to 100 mg/L) or a high dose (HD, 175 to 250 mg/L) in the drinking fluid. Survival of FHH rats and, to a lesser extent, F1 rats, was adversely affected by L-NAME treatment. All ACI rats except for one ACI-HD animal survived. In all strains, L-NAME caused a dose-dependent increase in SBP. At similar levels of SBP, the increase in functional renal damage, as indicated by the level of albuminuria, was higher in F1 compared with ACI, but lower compared with FHH. The same differences were found for the level of structural renal damage, as indicated by the incidence of glomerulosclerosis. Both the SBP and the average BP burden (SBP-Av), defined as SBP averaged over the period of follow-up, directly correlated with the level of albuminuria and incidence of glomerulosclerosis in all strains. However, the increase in the degree of renal damage per mmHg increase in SBP or SBP-Av was significantly higher in the F1 rats compared with ACI, but lower compared with FHH rats. Values for these F1 rats were closer to the ACI rats than to values for the FHH rats and increased above an SBP level of 180 mmHg. The F1 rats, being heterozygous for Rf-1 and Rf-2, as well as for other potential genes responsible for renal disease, were largely, but not completely, protected from hypertension-induced renal damage. It is concluded that complete susceptibility to hypertension-associated renal damage in rats primarily depends on the presence of predisposing genes for renal failure even after a significant increase in BP.