Genetic contamination of Dahl SS/Jr rats. Impact on studies of salt-sensitive hypertension

Brown-Norway chromosome 1 mitigates the upregulation of proinflammatory pathways in mTAL cells and subsequent age-related CKD in Dahl SS/JrHsdMcwi rats

Chronic kidney disease (CKD) has a strong genetic component; however, the underlying pathways are not well understood. Dahl salt-sensitive (SS)/Jr rats spontaneously develop CKD with age and are used to investigate the genetic determinants of CKD. However, there are currently several genetically diverse Dahl SS rats maintained at various institutions and the extent to which some exhibit age-related CKD is unclear. We assessed glomerulosclerosis (GS) and tubulointerstitial fibrosis (TIF) in 3- and 6-mo-old male and female SS/JrHsdMcwi, BN/NHsd/Mcwi [Brown-Norway (BN)], and consomic SS-Chr 1BN/Mcwi (SS.BN1) rats, in which chromosome 1 from the BN rat was introgressed into the genome of the SS/JrHsdMcwi rat. Rats were fed a 0.4% NaCl diet. GS (31 ± 3% vs. 7 ± 1%) and TIF (2.3 ± 0.2 vs. 0.5 ± 0.1) were significantly greater in 6-mo-old compared with 3-mo-old SS/JrHsdMcwi rats, and CKD was exacerbated in males. GS was minimal in 6- and 3-mo-old BN (3.9 ± 0.6% vs. 1.2 ± 0.4%) and SS.BN1 (2.4 ± 0.5% vs. 1.0 ± 0.3%) rats, and neither exhibited TIF. In SS/JrHsdMcwi and SS.BN1 rats, mean arterial blood pressure was significantly greater in 6-mo-old compared with 3-mo-old SS/JrHsdMcwi (162 ± 4 vs. 131 ± 2 mmHg) but not SS.BN1 (115 ± 2 vs. 116 ± 1 mmHg) rats. In 6-mo-old SS/JrHsdMcwi rats, blood pressure was significantly greater in females. RNA-sequencing analysis revealed that inflammatory pathways were upregulated in isolated medullary thick ascending tubules in 7-wk-old SS/JrHsdMcwi rats, before the development of tubule pathology, compared with SS.BN1 rats. In summary, SS/JrHsdMcwi rats exhibit robust age-related progression of medullary thick ascending limb abnormalities, CKD, and hypertension, and gene(s) on chromosome 1 have a major pathogenic role in such changes.NEW & NOTEWORTHY This study shows that the robust age-related progression of kidney disease in Dahl SS/JrHsdMcw rats maintained on a normal-salt diet is abolished in consomic SS.BN1 rats. Evidence that medullary thick ascending limb segments of SS/JrHsdMcw rats are structurally abnormal and enriched in proinflammatory pathways before the development of protein casts provides new insights into the pathogenesis of kidney disease in this model.

Development of mammary cancer in γ-irradiated F1 hybrids of susceptible Sprague-Dawley and resistant Copenhagen rats, with copy-number losses that pinpoint potential tumor suppressors

Copenhagen rats are highly resistant to mammary carcinogenesis, even after treatment with chemical carcinogens and hormones; most studies indicate that this is a dominant genetic trait. To test whether this trait is also dominant after radiation exposure, we characterized the susceptibility of irradiated Copenhagen rats to mammary carcinogenesis, as well as its inheritance, and identified tumor-suppressor genes that, when inactivated or mutated, may contribute to carcinogenesis. To this end, mammary cancer-susceptible Sprague-Dawley rats, resistant Copenhagen rats, and their F1 hybrids were irradiated with 4 Gy of γ-rays, and tumor development was monitored. Copy-number variations and allelic imbalances of genomic DNA were studied using microarrays and PCR analysis of polymorphic markers. Gene expression was assessed by quantitative PCR in normal tissues and induced mammary cancers of F1 rats. Irradiated Copenhagen rats exhibited a very low incidence of mammary cancer. Unexpectedly, this resistance trait did not show dominant inheritance in F1 rats; rather, they exhibited intermediate susceptibility levels (i.e., between those of their parent strains). The susceptibility of irradiated F1 rats to the development of benign mammary tumors (i.e., fibroadenoma and adenoma) was also intermediate. Copy-number losses were frequently observed in chromosome regions 1q52-54 (24%), 2q12-15 (33%), and 3q31-42 (24%), as were focal (38%) and whole (29%) losses of chromosome 5. Some of these chromosomal regions exhibited allelic imbalances. Many cancer-related genes within these regions were downregulated in mammary tumors as compared with normal mammary tissue. Some of the chromosomal losses identified have not been reported previously in chemically induced models, implying a novel mechanism inherent to the irradiated model. Based on these findings, Sprague-Dawley × Copenhagen F1 rats offer a useful model for exploring genes responsible for radiation-induced mammary cancer, which apparently are mainly located in specific regions of chromosomes 1, 2, 3 and 5.

Thick Ascending Limb Sodium Transport in the Pathogenesis of Hypertension

The thick ascending limb plays a key role in maintaining water and electrolyte balance. The importance of this segment in regulating blood pressure is evidenced by the effect of loop diuretics or local genetic defects on this parameter. Hormones and factors produced by thick ascending limbs have both autocrine and paracrine effects, which can extend prohypertensive signaling to other structures of the nephron. In this review, we discuss the role of the thick ascending limb in the development of hypertension, not as a sole participant, but one that works within the rich biological context of the renal medulla. We first provide an overview of the basic physiology of the segment and the anatomical considerations necessary to understand its relationship with other renal structures. We explore the physiopathological changes in thick ascending limbs occurring in both genetic and induced animal models of hypertension. We then discuss the racial differences and genetic defects that affect blood pressure in humans through changes in thick ascending limb transport rates. Throughout the text, we scrutinize methodologies and discuss the limitations of research techniques that, when overlooked, can lead investigators to make erroneous conclusions. Thus, in addition to advancing an understanding of the basic mechanisms of physiology, the ultimate goal of this work is to understand our research tools, to make better use of them, and to contextualize research data. Future advances in renal hypertension research will require not only collection of new experimental data, but also integration of our current knowledge.

Salt-sensitive (Rapp) rats from Envigo spontaneously develop accelerated hypertension independent of ovariectomy on a low-sodium diet

Inbred salt-sensitive (SS) rats developed by John Rapp and distributed by Harlan (SS/JrHsd) were shown to model ovariectomy-induced hypertension because on a low-sodium (LS) diet, ovariectomized SS (SS-OVX) animals became hypertensive in contrast to their sham-operated (SS-SHAM) normotensive littermates. After Harlan merged with Envigo in 2015, inconsistencies in the LS normotensive phenotype were reported. To further investigate these inconsistencies, we studied the effects of ovariectomy on SS and salt-resistant (SR) rats purchased from Envigo (SS/JrHsd/Env) between 2015 and 2017. The mean arterial pressure (MAP) in SS rats on a LS diet exceeded 160 mmHg at 7 mo old. Ovariectomy at 3 mo had no detectable effect on MAP from 4 to 7 mo, nor did ovariectomy at 1.5 mo significantly affect MAP at 10 mo in either strain; only strain differences in MAP were observed [MAP: SR-SHAM ( n = 7 rats), 102 ± 3 mmHg; SR-OVX ( n = 6 rats), 114 ± 1 mmHg; SS-SHAM ( n = 7 rats), 177 ± 6 mmHg; SS-OVX ( n = 5 rats), 190 ± 12 mmHg; where P < 0.0001 vs. SR, same ovarian-status for SS-SHAM and SS-OVX, respectively]. Whole genome sequencing revealed more genomic variants of SS/JrHsd/Env, including single nucleotide and insertion deletion polymorphisms and higher heterozygous/homozygous ratios compared with the reference genome, than for SS/JrHsd/Mcwi and SS/Jr rats maintained in Milwaukee, WI and Toledo, OH, respectively, and which still exhibit normal blood pressure on a LS diet. These findings demonstrate that the female SS/JrHsd/Env rat has genetically diverged from the original phenotype, which was normotensive on a LS diet when the ovaries were intact but rapidly developed hypertension when the ovaries were removed. Nonetheless, the SS/JrHsd/Env rat could be a valuable model that complements other animal models of spontaneous hypertension used to investigate mechanisms of essential hypertension.

Mitochondrial polymorphisms in rat genetic models of hypertension

Hypertension is a complex trait that has been studied extensively for genetic contributions of the nuclear genome. We examined mitochondrial genomes of the hypertensive strains: the Dahl Salt-Sensitive (S) rat, the Spontaneously Hypertensive Rat (SHR), and the Albino Surgery (AS) rat, and the relatively normotensive strains: the Dahl Salt-Resistant (R) rat, the Milan Normotensive Strain (MNS), and the Lewis rat (LEW). These strains were used previously for linkage analysis for blood pressure (BP) in our laboratory. The results provide evidence to suggest that variations in the mitochondrial genome do not account for observed differences in blood pressure between the S and R rats. However, variants were detected among the mitochondrial genomes of the various hypertensive strains, S, SHR, and AS, and also among the normotensive strains R, MNS, and LEW. A total of 115, 114, 106, 106, and 16 variations in mtDNA were observed between the comparisons S versus LEW, S versus MNS, S versus SHR, S versus AS, and SHR versus AS, respectively. Among the 13 genes coding for proteins of the electron transport chain, 8 genes had nonsynonymous variations between S, LEW, MNS, SHR, and AS. The lack of any sequence variants between the mitochondrial genomes of S and R rats provides conclusive evidence that divergence in blood pressure between these two inbred strains is exclusively programmed through their nuclear genomes. The variations detected among the various hypertensive strains provides the basis to construct conplastic strains and further evaluate the effects of these variants on hypertension and associated phenotypes.

Genetic analysis of inherited hypertension in the rat

Blood pressure is a quantitative trait that has a strong genetic component in humans and rats. Several selectively bred strains of rats with divergent blood pressures serve as an animal model for genetic dissection of the causes of inherited hypertension. The goal is to identify the genetic loci controlling blood pressure, i.e., the so-called quantitative trait loci (QTL). The theoretical basis for such genetic dissection and recent progress in understanding genetic hypertension are reviewed. The usual paradigm is to produce segregating populations derived from a hypertensive and normotensive strain and to seek linkage of blood pressure to genetic markers using recently developed statistical techniques for QTL analysis. This has yielded candidate QTL regions on almost every rat chromosome, and also some interactions between QTL have been defined. These statistically defined QTL regions are much too large to practice positional cloning to identify the genes involved. Most investigators are, therefore, fine mapping the QTL using congenic strains to substitute small segments of chromosome from one strain into another. Although impressive progress has been made, this process is slow due to the extensive breeding that is required. At this point, no blood pressure QTL have met stringent criteria for identification, but this should be an attainable goal given the recently developed genomic resources for the rat. Similar experiments are ongoing to look for genes that influence cardiac hypertrophy, stroke, and renal failure and that are independent of the genes for hypertension.

Genetic analysis of rat chromosome 1 and the Sa gene in spontaneous hypertension

Linkage studies in segregating populations derived from the spontaneously hypertensive rat (SHR) indicate that a blood pressure quantitative trait locus exists on rat chromosome 1 in the vicinity of the Sa gene. On the basis of these findings and the observation of increased renal expression of the Sa gene in SHR versus normotensive rats, the Sa gene has been proposed as a candidate gene for spontaneous hypertension. In SHR congenic strains, we and others have found that replacement of a segment of SHR chromosome 1 that contains the Sa gene with the corresponding chromosome segment from a normotensive Brown Norway (BN) rat or Wistar-Kyoto rat can reduce blood pressure. To test whether the Sa gene is necessary for the effect of this region of chromosome 1 on blood pressure, we studied a new SHR congenic subline that harbors a smaller segment of BN chromosome 1 that does not include the Sa gene. Transfer of this subregion of chromosome 1 from the BN rat onto the SHR background was associated with significant reductions in blood pressure comparable to those previously observed on transfer of a larger region of chromosome 1 that included the Sa gene. Thus, in the SHR-BN model of hypertension, the results of these mapping studies (1) demonstrate that molecular variation in the Sa gene is not required for the effect of this region of chromosome 1 on blood pressure and (2) should direct attention toward other candidate genes within the differential chromosome segment of the new congenic subline.

Nitric oxide-induced inhibition of transport by thick ascending limbs from Dahl salt-sensitive rats

The factor responsible for salt sensitivity of blood pressure in Dahl rats is unclear but presumably resides in the kidney. We tested the hypotheses that (1) thick ascending limbs of Dahl salt-sensitive rats (DS) absorb more NaCl than those of Dahl salt-resistant rats (DR) and (2) NO inhibits transport to a lesser extent in thick ascending limbs from DS. We found that basal chloride absorption (J(Cl)) by thick ascending limbs from DR was 105.8+/-10.0 pmol. mm(-1). min(-1) (n=6). Ten and 100 micromol/L spermine NONOate, an NO donor, decreased J(Cl) in DR to 65.8+/-8.5 and 46.8+/-7.0 pmol. mm(-1). min(-1), respectively. Basal J(Cl) in DS was 131.6+/-13.4 pmol. mm(-1). min(-1) (n=7). In DS, 10 and 100 micromol/L spermine NONOate decreased J(Cl) to 111.5+/-12.8 and 46.8+/-6.2 pmol. mm(-1). min(-1), respectively. No difference was observed in basal or NO-inhibited Na absorption by cortical collecting ducts or in basal or NO-inhibited oxygen consumption by inner medullary collecting ducts. Because NO acts via generation of cGMP, we measured cGMP production by thick ascending limbs from DS and DR to see whether a difference in cGMP production could account for the difference in basal or NO-inhibited transport. Basal rates of cGMP production were similar between the 2 strains. Although NO increased cGMP production by thick ascending limbs from both strains, no difference existed between DS and DR. We concluded that the reduced ability of NO to block transport in thick ascending limbs in DS may account for at least part of the salt sensitivity of blood pressure in this strain.

Altered protein kinase C activation of Na+/Ca2+ exchange in mesangial cells from salt-sensitive rats

The purpose of these studies was to determine whether there is a defect in protein kinase C (PKC) regulation of the Na+/Ca2+ exchanger in cultured mesangial cells (MC) from Dahl/Rapp salt-sensitive (S) and salt-resistant (R) rats. R and S MCs were cultured, grown on coverslips, and loaded with fura 2 for measurement of single cell cytosolic calcium concentration ([Ca2+]i) in a microscope-based photometry system. Studies were performed in cells that were exposed to serum (serum fed) and in cells that were serum deprived for 24 h. Baseline [Ca2+]i values measured in a Ringer solution containing 150 mM NaCl were similar between R and S MCs in both serum-fed and serum-deprived groups, although baseline [Ca2+]i values were uniformly higher in the serum-deprived groups. Exchanger activity was assessed by reducing extracellular Na (Nae) from 150 to 2 mM, which resulted in movement of Na+ out of and Ca2+ into these cells (reverse-mode Na+/Ca2+ exchange). PKC was activated in these cells with 15-min exposure to 100 nM phorbol 12-myristate 13-acetate (PMA). In the absence of PMA, the change in [Ca2+]i (Delta[Ca2+]i) with reduction in Nae was similar between R and S MCs in both serum-fed and serum-deprived groups, although the magnitude of Delta[Ca2+]i was enhanced by serum deprivation. In both serum-fed and serum-deprived groups, PMA significantly increased Delta[Ca2+]i in R but not S MCs. Upregulation of exchanger activity in R MCs could be abolished by prior 24-h exposure to PMA, a maneuver that downregulates PKC activity. Other studies were performed to evaluate exchanger protein expression using monoclonal and polyclonal antibodies. Immunoblots of PMA-treated cells revealed an increase in the levels of 70- and 120-kDa proteins in the crude membrane fraction of R but not S MCs, an increase which was abrogated by prior 24-h PMA pretreatment and corresponded to reduction in the 70-kDa protein in the crude cytosolic fraction. These data demonstrate that PKC enhances Na+/Ca2+ exchange activity in MCs from R but not from S rats, suggesting that there may be a defect in the PKC-Na+/Ca2+ exchange regulation pathway in MCs of S rats.

Effect of chromosome 19 transfer on blood pressure in the spontaneously hypertensive rat

Linkage studies in the spontaneously hypertensive rat (SHR) have suggested that a gene or genes regulating blood pressure may exist on rat chromosome 19 in the vicinity of the angiotensinogen gene. To test this hypothesis, we measured blood pressure in SHR progenitor and congenic strains that are genetically identical except for a segment of chromosome 19 containing the angiotensinogen gene transferred from the normotensive Brown Norway (BN) strain. Transfer of this segment of chromosome 19 from the BN strain onto the genetic background of the SHR induced significant decreases in systolic and diastolic blood pressures in the recipient SHR chromosome 19 congenic strain. To test for differences in angiotensinogen gene expression between the congenic and progenitor strains, we measured angiotensinogen mRNA levels in a variety of tissues, including aorta, brain, kidney, and liver. We found no differences between the progenitor and congenic strains in the angiotensinogen coding sequence or in angiotensinogen expression that would account for the blood pressure differences between the strains. In addition, no significant differences in plasma levels of angiotensinogen or plasma renin activity were detected between the 2 strains. Thus, transfer of a segment of chromosome 19 containing angiotensinogen from the BN rat into the SHR induces a decrease in blood pressure without inducing any major changes in plasma angiotensinogen levels or plasma renin activity. These results indicate that the differential chromosome segment trapped in the SHR chromosome 19 congenic strain contains a quantitative trait locus that influences blood pressure in the SHR but that this blood pressure effect is not explained by differences in plasma angiotensinogen levels or angiotensinogen expression.

Abnormal regulation of proximal tubule renin mRNA in the Dahl/Rapp salt-sensitive rat

BACKGROUND

The precise pathogenesis of salt-sensitive hypertension in the Dahl rat is unknown. Abnormalities in renal hemodynamics and NaCl handling have been implicated, and may relate to changes in the activity of the intrarenal renin-angiotensin system.

METHODS

Circulating, juxtaglomerular and intrarenal (glomerular and proximal tubular) renin were studied in Dahl/Rapp salt-sensitive and salt-resistant rats fed with a normal (0.5%) or high (4%) NaCl diet. Circulating and juxtaglomerular renin were assessed by measurement of plasma renin activity and renin secretory rates. Glomerular and proximal tubular renin mRNA were assessed by microdissection and quantitative competitive RT-PCR.

RESULTS

Circulating and juxtaglomerular renin were suppressed by high dietary NaCl in salt-sensitive rats (plasma renin activity, 0.5%, 10.9 +/- 0.7 vs. 4%, 7.9 +/- 0.3 ng/ml/hr, P < 0.05; renin secretory rate, 0.5% 220 +/- 32 vs. 4%, 58 +/- 5 ng/mg/hr, P < 0.05). Glomerular renin mRNA was also suppressed by the higher salt diet in salt-sensitive animals (0.5%, 411 +/- 84 vs. 4%, 67 +/- 22 x 103 copies/glomerulus, P < 0.05). In contrast, proximal tubular renin was not suppressed by a high NaCl diet in salt-sensitive animals (0.5%, 13.9 +/- 2.7 vs. 4%, 12.1 +/- 3.6 x 103 copies/mm tubule, P = NS), but was suppressed in salt-resistant rats (0.5%, 9.5 +/- 2.8 vs. 4%, 3.2 +/- 1.2 x 103 copies/mm, P < 0. 05).

CONCLUSIONS

Failure to suppress proximal tubular renin in response to high dietary NaCl may result in increased local generation of angiotensin II and enhanced proximal tubular NaCl absorption, and thereby contribute to the generation of salt sensitive hypertension.

The alpha1 Na,K-ATPase gene is a susceptibility hypertension gene in the Dahl salt-sensitiveHSD rat

Despite the prevalence of essential hypertension, its underlying genetic basis has not been elucidated due to the complexities of its determinants. To identify a hypertension susceptibility gene, we used an approach that integrates molecular, transgenic, and genetic analysis using Dahl salt-sensitive (S) and Dahl salt-resistant (R) rats ascertained for genotype and phenotype. To determine the role of the Dahl S Q276L alpha1 Na,K-ATPase gene variant, we developed transgenic Dahl S rats bearing the Dahl R wild-type (wt) alpha1 Na, K-ATPase cDNA directed by the cognate wt promoter region, Tg[wtalpha1]. Transgenic Dahl S rats exhibited less salt-sensitive hypertension, less hypertensive renal disease, and longer life span when compared with non-transgenic Dahl S controls. Total chromosome 2 linkage analysis of F2(SxR) male rats detects cosegregation of the alpha1 Na,K-ATPase locus with salt-sensitive hypertension. These data support the alpha1 Na,K-ATPase gene as a susceptibility gene for salt-sensitive hypertension in the Dahl S rat model, and provide the basis for the study of the alpha1 Na,K-ATPase locus in human hypertension.

Is the nitric oxide system involved in genetic hypertension in Dahl rats?

To address this issue, a series of genetic tests were carried out. Linkage studies showed that the inducible nitric oxide synthase (Nos2) locus cosegregated with blood pressure in three F2 populations originated from crosses of Dahl salt-sensitive (S) rats with rats of various normotensive strains. However, the brain nitric oxidase synthase (Nos1) and endothelial nitric oxide synthase (Nos3) loci did not cosegregate with blood pressure in five F2 populations. Thus, only Nos2, but not Nos1 and Nos3, was considered as a candidate gene for being a quantitative trait locus (QTL) for blood pressure in the S rat. To further test this hypothesis, congenic strains were constructed by substituting regions on Chromosome 10 of the S rat with the homologous regions of the Milan normotensive (MNS) rat. Results showed that the chromosome region including Nos2 did not contain a blood pressure QTL. In consequence, Nos2 per se is not supported as a candidate QTL capable of causing a blood pressure difference between the S and MNS rats. Nevertheless, the nitric oxide system appears to be involved secondarily in the regulation of blood pressure in the S rat, as evidenced by physiological data.

Vascular smooth muscle nitric oxide synthase anomalies in Dahl/Rapp salt-sensitive rats

Salt-sensitive hypertension in the Dahl/Rapp rat (S strain) is prevented by L-arginine. Based on the observations that dexamethasone prevented the antihypertensive effect of L-arginine in these animals and the suggestion that a locus in or near an inducible nitric oxide synthase (NOS) gene on chromosome 10 cosegregated with hypertension in some F2 crosses that utilized the S rat, the present study explored the hypothesis that the vascular smooth muscle isoform of inducible NOS (NOS2) was abnormal in S rats. Primary cultures of aortic smooth muscle cells from S rats demonstrated impaired inducible NO production, which improved with increased L-arginine in the medium. Sequence analysis identified a single T-->C transversion that produced an amino acid substitution (S714P) between the FAD and FMN binding sites and a restriction fragment length polymorphism. This restriction fragment length polymorphism was present only in S rats. The mutation of NOS2 and the role of this enzyme in the pathogenesis of salt-sensitive hypertension in the Dahl/Rapp rat require further investigation.

Modulation of blood pressure in the Dahl SS/jr rat by embryo transfer

Gestational hypertension and malnutrition are associated with hypertension and ischemic heart disease in the adult human. The impact of the gestational environment on the adult blood pressure in two well-characterized genetically homogeneous rat strains, the hypertensive SS/jr and normotensive SR/jr, was studied by cross-fostering within 6 hours of birth and by embryo transplantation with the recipient dam nursing the transplanted pups. Systolic blood pressure (BP) was measured by tail-cuff plethysmography twice a week after the age of 7 weeks. The lactational environment (cross-fostering) had no effect on blood pressure. Embryo transfer between like strains had no effect on the development of hypertension, nor did the BP of R transferred to S (RetS) differ from that of normal R or RetR. At 7 weeks of age, the BP of SetR was significantly lower than that of S or SetS (P<.01) and was similar to that of RetR and R. With age, the blood pressures of the S, SetS and SetR increased at approximately the same rate but from a significantly different baseline. Salt-sensitivity in the S and resistance in the R were not altered. The protective effect of the R gestational environment on SetR female BP was abrogated during whelping and lactation. Embryo transfer and cross-fostering did not alter the weight of rats older than 7 weeks. Because the BP of the R dams were significantly lower than that of the S dams, these studies do not distinguish between the effects of the R dams' lower blood pressure per se and hormonal influences of the R uterus on the S blood pressure phenotype.

Effect of renin gene transfer on blood pressure in the spontaneously hypertensive rat

To investigate whether molecular variation in the renin gene contributes to the greater blood pressure of spontaneously hypertensive rats (SHR) versus normotensive Brown Norway (BN) rats, we measured blood pressure in an SHR progenitor strain and an SHR congenic strain that are genetically identical except at the renin gene and an associated segment of chromosome 13 transferred from the BN strain. Backcross breeding and molecular selection at the renin locus were used to create the SHR congenic strain (designated SHR.BN-Ren) that carries the renin gene transferred from the normotensive BN strain. We found that transfer of the renin gene from the BN strain onto the genetic background of the SHR did not decrease blood pressure in rats fed either a normal or high-salt diet. In fact, the systolic blood pressures of the SHR congenic rats tended to be slightly greater than the systolic blood pressures of the SHR progenitor rats. However, the congenic strain exhibited lower serum high-density lipoprotein cholesterol, and greater levels of total cholesterol, very-low-density lipoprotein, and intermediate-density lipoprotein cholesterol during administration of a high-fat, high-cholesterol diet. These findings demonstrate that (1) under the environmental circumstances of the current study, the greater blood pressure of SHR versus BN rats cannot be explained by strain differences in the renin gene and (2) a quantitative trait locus affecting lipid metabolism exists on chromosome 13 within the transferred chromosome segment. The SHR.BN-Ren congenic strain may provide a useful new animal model for studying the interaction between high blood pressure and dyslipidemia in cardiovascular disease.

Genetic isolation of a chromosome 1 region affecting blood pressure in the spontaneously hypertensive rat

Recent linkage studies in the spontaneously hypertensive rat (SHR) suggest that a blood pressure regulatory gene or genes may be located on rat chromosome 1q. To investigate this possibility, we replaced a region of chromosome 1 in the SHR (defined by the markers D1Mit3 and Igf2) with the corresponding chromosome segment from the normotensive Brown-Norway (BN) strain. In male SHR congenic rats carrying the transferred BN chromosome segment, 24-hour average systolic and diastolic blood pressures were significantly lower than in male progenitor SHR. Polymerase chain reaction genotyping using 60 polymorphic microsatellite markers dispersed throughout the genome confirmed the congenic status of the new strain designated SHR.BN-D1Mit3/Igf2. These findings provide direct evidence that a blood pressure regulatory gene exists on the differential segment of chromosome 1 that is sufficient to decrease blood pressure in the SHR. The SHR.BN-D1Mit3/Igf2 congenic strain represents an important new model for fine mapping and characterization of genes on chromosome 1 involved in the pathogenesis of spontaneous hypertension.

Interval mapping and congenic strains for a blood pressure QTL on rat chromosome 13

The renin locus (Ren) on rat Chromosome (Chr) 13 had previously been shown to cosegregate with blood pressure in crosses involving Dahl salt-sensitive (S) and Dahl salt-resistant (R) rats. In the present work, interval mapping of blood pressure on Chr 13 with a large F2 (S x R), n = 233, population yielded a maximum LOD = 4.2 for linkage to blood pressure, but the quantitative trait locus (QTL) was only poorly localized to a large 35-centiMorgan (cM) segment of Chr 13. In the linkage analysis, the S-rat QTL allele (S) was associated with higher, and the R-rat QTL allele (R) with lower blood pressure, the difference between homozygotes being about 20 mm Hg. A congenic strain was made by introgressing the R-rat Ren allele into the recipient S strain. This congenic strain showed a 24 mm Hg reduction (P = 0.004) in blood pressure compared with S rats for rats fed 2% NaCl diet for 24 days; this difference was confirmed by two other independent tests. Two congenic substrains were derived from the first congenic strain with shorter R Chr 13 segments on the S background. Comparisons among these congenic strains showed that a blood pressure QTL was in the 24-cM chromosomal segment between Syt2 and D13M1Mit108. This segment does not include the renin locus, which is thus excluded from being the gene on rat Chr 13 responsible for genetic differences in blood pressure detected by linkage analysis.

Genetic isolation of a region of chromosome 8 that exerts major effects on blood pressure and cardiac mass in the spontaneously hypertensive rat

The spontaneously hypertensive rat (SHR) is the most widely studied animal model of essential hypertension. Despite > 30 yr of research, the primary genetic lesions responsible for hypertension in the SHR remain undefined. In this report, we describe the construction and hemodynamic characterization of a congenic strain of SHR (SHR-Lx) that carries a defined segment of chromosome 8 from a normotensive strain of Brown-Norway rats (BN-Lx strain). Transfer of this segment of chromosome 8 from the BN-Lx strain onto the SHR background resulted in substantial reductions in systolic and diastolic blood pressure and cardiac mass. Linkage and comparative mapping studies indicate that the transferred chromosome segment contains a number of candidate genes for hypertension, including genes encoding a brain dopamine receptor and a renal epithelial potassium channel. These findings demonstrate that BP regulatory gene(s) exist within the differential chromosome segment trapped in the SHR-Lx congenic strain and that this region of chromosome 8 plays a major role in the hypertension of SHR vs. BN-Lx rats.

Transfer of a salt-resistant renin allele raises blood pressure in Dahl salt-sensitive rats

To evaluate the role of the renin gene in the development of hypertension in Dahl salt-sensitive rats (SS/Jr/Hsd), we derived a congenic strain of rats homozygous for the salt-resistant renin allele (S/renrr) and compared them with a control strain homozygous for the salt-sensitive renin allele (S/ren(ss). Mean arterial pressure was significantly higher in 12-week-old S/renrr rats fed a high salt (8.0%) diet for 3 weeks than in S/ren(ss) rats or in SS/Jr/Hsd rats rederived from the foundation colony we used to generate the cogenic strain (195 +/- 3 [n = 49] versus 168 +/- 3 [n = 17] or 161 +/- 3 [n = 16] mm Hg). Mean arterial pressure was also higher in S/renrr rats than in S/ren(ss) rats raised from birth on either a very low salt (0.1%) diet (119 +/- 9 [n = 6] versus 100 +/- 7 [n = 7] mm Hg) or a low salt (0.4%) diet (143 +/- 1 [n = 22] versus 117 +/- 3 [n = 10] mm Hg). Plasma renin activity of S/renrr rats was significantly higher than that of S/ren(ss) rats fed a very low salt diet (5.7 +/- 2.0 versus 1.8 +/- 0.3) ng angiotensin l/mL per hour), a low salt diet (4.4 +/- 1.0 versus 1.1 +/- 0.3), or a high salt diet (1.5 +/- 0.2 versus 0.9 +/- 0.1). Urinary protein excretion was greater in S/renrr rats than in S/ren(ss) rats fed a high salt diet (244.2 +/- 48.5 versus 43.6 +/- 19.5 mg/24 h), and this was associated with significant reductions in renal blood flow (3.3 +/- 0.6 versus 4.6 +/- 0.5 mL/min per gram kidney weight) and glomerular filtration rate (0.49 +/- 0.11 versus 0.82 +/- 0.08 mL/min per gram kidney weight). Captopril (20 mg/kg i.v.) had no effect on blood pressure in S/ren(ss) rats fed a low salt diet, but it lowered blood pressure by 20 mm Hg in S/ren(rr) rats to the same level seen in untreated S/ren(ss) rats. Chronic administration of captopril (5 mg/100 mL drinking water) reduced blood pressure in S/renrr rats fed a high salt diet (170 +/- 5 mm Hg) to the same level seen in untreated S/ren(ss) rats, whereas it had no significant effect on blood pressure in S/ren(ss) rats. These results indicate that transfer of a salt-resistant renin allele to SS/Jr/Hsd rats raises plasma renin activity and augments the severity of hypertension and renal disease.

Plasma and renal prorenin/renin, renin mRNA, and blood pressure in Dahl salt-sensitive and salt-resistant rats

We measured plasma prorenin and renin levels, renal renin mRNA, renal anti-renin and anti-prorenin-prosequence immunoreactivity, and blood pressure in maturing Brookhaven Dahl salt-sensitive (Dahl S) and salt-resistant (Dahl R) rats during 14 days of low (0%), medium (0.4%), or high 4%) NaCl diets. Blood pressure was higher in Dahl S rats and did not increase with high NaCl. Seven-week-old Dahl R rats had twofold and sixfold higher levels of plasma prorenin and renal prosequence immunoreactivity, respectively, which by 9 weeks were the same as in Dahl S rats. The anti-renin antiserum, BR1-5, was found to detect prorenin better than renin; Dahl S rats had suppressed renal anti-renin immunoreactivity relative to Dahl-R rats. Dahl R rats were unresponsive to high NaCl, whereas in Dahl S rats, plasma renin and renal prosequence immunoreactivity fell by 90% (P < .01), renal anti-renin immunoreactivity and renal renin MRNA fell by 35% (P < .05 for both), and plasma prorenin fell by 30% (P = NS). NaCl depletion increased prorenin/renin parameters similarly in both strains. There were direct relationships among all of the prorenin/renin parameters. Between low and high salt diets in Dahl S rats, plasma renin increased 20-fold, plasma total renin (renin plus prorenin) and renal renin mRNA both increased threefold, and plasma prorenin increased twofold. The results indicate that under steady-state conditions, plasma and renal renin/prorenin parameters change concordantly and that plasma total renin (renin plus prorenin) reflects changes in renal renin mRNA. The lower blood pressure of Dahl R rats is associated with later maturation-related declines in plasma and renal prorenin. Suppression of plasma renin may delay the salt-induced blood pressure rise in Dahl S rats. Finally, the renin system and blood pressure of Dahl R rats have remarkable disregard for a high salt diet.

Genetic characterization of the "new" Harlan Sprague Dawley Dahl salt-sensitive rats

In 1994, it was reported that Dahl salt-sensitive SS/Jr rats supplied by Harlan Sprague Dawley were genetically contaminated and resistant to the pressor effects of a high salt diet. Harlan Sprague Dawley subsequently developed new pedigree expansion and production colonies from their foundation colony to supply new, purportedly inbred, Harlan Sprague Dawley SS/Jr (S(HSD)). To evaluate the genetic integrity and salt sensitivity of thse new S(HSD), we performed genotyping (microsatellite DNA markers) and phenotyping (radiotelemetric arterial pressure) of 12 S(HSD), 16 "authentic" SS/Jr from the inbred colony of John Rapp (S(Rapp)), 9 Harlan Sprague Dawley salt-resistant SR/Jr (R(HSD)), and (genotyping only) 6 known "contaminated" Harlan Sprague Dawley Dahl SS/Jr (S*). In the genotyping studies, 20 of 22 markers revealed polymorphisms between S(Rapp) and S* and 18 were polymorphic between S(Rapp) and R(Rapp), but none of the 22 markers revealed polymorphisms between S(Rapp) and the new S(HSD). The phenotyping studies showed that during an ultra-low salt diet, mean arterial pressure was higher (P < .05) in both authentic S(Rapp) (129 +/- 2 mm Hg; mean +/- SE) and new S(HSD) (120 +/- 2 mm Hg) than in R(HSD) (93 +/- 1 mm Hg). A high salt diet increased mean arterial pressure in every S(HSD) and S(Rapp). Increases in mean arterial pressure after 4 weeks of a high salt diet were significantly (P < 0.05) greater in authentic S(Rapp) (+51 +/- 3 mm Hg) than in new S(HSD) (+39 +/- 3 mm Hg). In addition, salt-induced mortality was significantly greater in S(Rapp) (62.5%) than S(HSD) (8.3%) after 8 weeks (P < 0.01). S(HSD) were genotypically indistinguishable from S(Rapp), had an elevated arterial pressure on a low salt diet, and had a pressor response to salt. Thus, the new S(HSD) supplied to us had several characteristics of inbred Dahl SS/Jr and did not have evidence of the previously detected genetic contamination. However, phenotypic characteristics such as body weight, salt-induced hypertension, and mortality were significantly different in S(HSD) compared with S(Rapp). This may reflect genetic differences between these two strains or differences in environmental factors and suggests that the S(HSD) and S(Rapp) may now constitute distinct substrains of Dahl SS/Jr.

Role of 20-HETE in elevating loop chloride reabsorption in Dahl SS/Jr rats

In vivo tubular perfusion experiments were performed in normotensive Dahl salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) rats maintained from birth on a low salt (0.4% NaCl) diet to examine the role of 20-HETE in elevating loop Cl- transport in SS/Jr rats. Chloride reabsorption in the loop of Henle was significantly greater in SS/Jr than in SR/Jr rats (77 +/- 2% versus 57 +/- 3% of the perfused Cl- load). When the renal metabolism of arachidonic acid by P450 was blocked by the addition of 17-octadecynoic acid (10 micromol/L) to the perfusate, loop Cl- transport increased in SR/Jr rats to 70 +/- 2% of the delivered Cl- load, but it had no effect in SS/Jr rats. Conversely, addition of 20-HETE (10 micromol/L) to the perfusate lowered loop Cl- transport in S rats to 60 +/- 2% of perfused Cl- load, but it had no effect in SR/Jr rats. Addition of another endogenously formed HETE to the perfusate, 15-HETE (20 micromol/L), had no effect on Cl- reabsorption in the loop of Henle of SS/Jr rats. These findings indicate that endogenously produced P450 metabolites of arachidonic acid regulate Cl- transport in the loop of Henle of the rat in vivo and support the view that a diminished production of 20-HETE in the outer medulla of SS/Jr rats contributes to the elevation in loop Cl- transport and the resetting of the pressure-natriuresis relation in these animals.

Cytochrome P4504A genotype cosegregates with hypertension in Dahl S rats

Recent studies indicate that the production of 20-HETE by a P4504A2 enzyme in the outer medulla of the kidney is reduced in Dahl salt-sensitive (SS/Jr) rats, but the contribution of this abnormality to the elevation in loop Cl- transport and development of hypertension in this model is unknown. THe present study found that alleles at the locus for the P4504A2 gene cosegregate with blood pressure in an F2 population (n=151) derived from a cross between SS/Jr and Lewis rats (P < .0001). The P4504A2 locus is located in a region on rat chromosome 5 where a blood pressure quantitative trait locus was previously detected. Systolic blood pressure averaged 201 +/- 6 mm Hg in rats with the SS genotype (n=36), 192 +/- 4 mm Hg in SL genotype rats (n=77), and 169 +/- 3 mm Hg in LL genotype rats (n=38). In further studies, we confirmed that there are phenotypic differences in the expression of the P4504A2 gene in the kidneys of SS/Jr and Lewis rats. Although the production of 20-HETE from 14C-arachidonic acid was similar in microsomes prepared from the renal cortex of SS/Jr and Lewis rats (54 +/- 3 versus 55 +/- 3 pmol/min/mg protein), the production of 20-HETE in microsomes prepared from the outer medulla (OM) was markedly reduced in SS/Jr rats (2.8 +/- 0.8 versus 6.7 +/- 1 pmol/min/mg protein). The diminished production of 20-HETE in the OM was due to a threefold reduction in the level of P4504A2 protein. These results suggest that an altered expression of the P4504A2 enzyme in the OM may contribute to the development of hypertension in SS/Jr rats.

Effects of renin gene transfer on blood pressure and renin gene expression in a congenic strain of Dahl salt-resistant rats

To investigate whether a BP-regulatory locus exists in the vicinity of the renin locus on rat chromosome 13, we transferred this chromosome segment from the Dahl salt-sensitive (S) rat onto the genetic background of the Dahl salt-resistant (R) rat. In congenic Dahl R rats carrying the S renin gene and fed an 8% salt diet, systolic BP was significantly lower than in progenitor Dahl R rats: 127 +/- 1 mmHg versus 138 +/- 4 mmHg, respectively (P < 0.05). Moreover, the decreased BP in the congenic Dahl R strain was associated with decreased kidney renin mRNA and decreased plasma renin concentration. These findings demonstrate that the Dahl S strain carries alleles in or near the renin locus that confer lower plasma renin concentration and lower BP than the corresponding alleles in the Dahl R strain, at least when studied on the genetic background of the Dahl R rat and in the environment of a high salt diet. The occurrence of coincident reductions in kidney renin mRNA, plasma renin concentration, and BP after interstrain transfer of naturally occurring renin gene variants strongly suggests that genetically determined variation in renin gene expression can affect BP.

Use of simple sequence length polymorphisms for genetic characterization of rat inbred strains

Genetic monitoring is an essential component of colony management and for the rat has been accomplished primarily by using immunological and biochemical markers. Here, we report that simple sequence length polymorphisms (SSLPs) are a faster and more economical way of monitoring inbred strains of rats. We characterized 61 inbred strains of rats, using primer pairs for 37 SSLPs. Each of these loci appeared to be highly polymorphic, with the number of alleles per locus ranging between 3 and 14 and, as a result, all the 61 inbred strains tested in this study could be provided with a unique strain profile. These strain profiles are also used for estimating the degree of similarity between strains. This information may provide the rationale in selecting strains for genetic crosses or for other specific purposes.

Reciprocal regulation of cardiac Na-K-ATPase and Na/Ca exchanger: hypertension, thyroid hormone, development

Inhibiting cardiac Na pump activity decreases the driving force for the Na/Ca exchanger transport that increases cellular Ca stores and contractility. Decreased abundance of Na pumps would be expected to have the same effect as decreased activity unless there was reciprocal regulation of Na/Ca exchanger expression to oppose the effects of depressed Na pump activity on intracellular Ca stores. The aim of this study was to test the hypothesis that cardiac Na/Ca exchanger abundance is regulated in a reciprocal fashion to Na-K-ATPase abundance in a number of models known to have altered Na-K-ATPase abundance. In renovascular hypertension, cardiac ventricular Na-K-ATPase alpha 1-levels are unaltered, alpha 2-isoform subunit mRNA and protein levels decrease to 0.76 +/- 0.06 and 0.56 +/- 0.07 of control, respectively, and the Na/Ca exchanger protein (not mRNA) increased 1.35 +/- 0.11-fold. In the transition from hypothyroid to hyperthyroid cardiac alpha 1 doubles, alpha 2-protein increases 8.83 +/- 1.06-fold, and the Na/Ca exchanger protein decreases to 0.64 +/- 0.11. A similar pattern was seen during cardiac development in the preweaning rat heart. Treatment with the antiarrhythymic amiodarone has no effect on alpha 1, decreases alpha 2-protein expression to 0.51 +/- 0.08 of control, and increases exchanger expression 1.42 +/- 0.16-fold. In conclusion, the reciprocal regulation of the Na/Ca exchanger and of Na-K-ATPase alpha 2-expression provides evidence for a homeostatic mechanism that would oppose the changes in cellular Ca stores driven by the changes in Na-K-ATPase activity.

Alpha 2-adrenoceptors in brain and kidney during development of hypertension in Dahl-Iwai salt-sensitive rats

BACKGROUND

Both renal and extrarenal factors have been considered to contribute to the development of hypertension in Dahl salt-sensitive rats, but contents of both factors have not been established precisely.

AIM

To clarify the role of those factors in the sympathetic nervous system, we examined the regulation of alpha2-adrenoceptors in the lower brainstem and the renal tubular basolateral membranes simultaneously during the development of salt-induced hypertension in Dahl-Iwai salt-sensitive rats.

METHODS

Dahl-Iwai salt-sensitive or resistant rats were fed a high (8.0% NaCl)- or low (0.3%)- salt diet from 4 to 6 or 10 weeks of age. At 4, 6 and 10 weeks of age, the plasma membranes of the lower brainstem and the renal tubular basolateral membranes were obtained simultaneously and alpha 2-adrenoceptors were quantified by a radioligand binding assay using 3H-rauwolscine.

RESULTS

In the salt-sensitive rats, systolic blood pressure was significantly higher in those fed a high-salt diet than in those fed a low-salt diet. In the salt-resistant rats, both the high- and the low-salt groups showed similar blood pressure levels. At 6 weeks of age, alpha 2-receptor densities of the salt-sensitive rats fed a high-salt diet were lower in the lower brainstem and higher in the renal basolateral membranes than those fed a low-salt diet. In contrast, in the salt-resistant rats, both the high- and the low-salt groups had similar densities. At 10 weeks of age, the difference between the high- and the low-salt groups in the salt-sensitive rats disappeared in both the brainstem and the renal basolateral membranes.

CONCLUSIONS

Alpha 2-adrenoceptor regulation in the brainstem and the renal basolateral membranes differs between Dahl-Iwai salt-sensitive and salt-resistant rats. The modulation of alpha 2-adrenoceptors by a high salt intake may be essential particularly in the early phase of the development of salt-induced hypertension.

Molecular variants in the P450c11AS gene as determinants of aldosterone synthase activity in the Dahl rat model of hypertension

Dahl salt-sensitive (S) and salt-resistant (R) rats are widely used to study genetic determinants of salt-sensitive hypertension. Differences in blood pressure under a high sodium diet in these two strains may be due to differences in the synthesis of 18-OH-11-deoxycorticosterone (18-OH DOC). This difference in 18-OH-DOC synthesis is due to mutations in the Dahl R rat's gene for P450c11 beta (11 beta-hydroxylase), an adrenal enzyme involved in the synthesis of both corticosterone and 18-OH DOC from 11-deoxycorticosterone. Aldosterone/renin ratios in plasma and in the adrenals are greater in Dahl S than R rats, suggesting an altered physiologic relationship between the renin-angiotensin and aldosterone systems between these strains. We demonstrate that the mRNA for P450c11AS, (aldosterone synthase), an enzyme required for aldosterone synthesis, is identical in the Dahl S rat and in normotensive Sprague-Dawley rats, but that P450c11AS mRNA from the Dahl R rat contains 7 mutations that result in two amino acid substitutions. These two changes result in a form of P450c11AS that has a greater apparent Vmax and lower apparent Km, resulting in an enzyme that catalyzes the conversion of 11-deoxycorticosterone to aldosterone at a greater rate in Dahl R rats than the P450c11AS in Dahl S rats or Sprague-Dawley rats. Although plasma and adrenal renin are lower in Dahl S versus R rats, the regulation of P450c11AS mRNA expression in rats fed a low and high salt diet are identical in these strains. The current findings may explain both the reduced aldosterone concentrations and increased aldosterone/renin ratios previously reported in the Dahl S versus Dahl R rat.

Sustained hypertension in Dahl rats. Negative correlation of agonist response to blood pressure

The perfused mesenteric vasculature of Dahl salt-sensitive rats on a high salt diet for 5 days (prehypertensive or early hypertensive) is selectively supersensitive to norepinephrine. The present goal was to determine whether that supersensitivity was maintained as hypertension developed. Littermates of salt-sensitive and salt-resistant rats (Dahl Brookhaven strain) were followed on low or high salt for up to 6 weeks. Systolic blood pressure was elevated in the salt-sensitive, high salt rats after 3 or 6 weeks but not after 5 days of the diet. The perfused mesenteric vascular beds from salt-sensitive rats were supersensitive to norepinephrine and nerve stimulation but not to potassium chloride when the rats had been maintained for 5 days or 3 weeks on the high salt diet. However, responses to norepinephrine declined after 6 weeks of the high salt diet. To determine whether sustained high blood pressure has a negative effect on mesenteric vascular responses, we conducted additional experiments with perfused mesenteric vascular beds from salt-sensitive Brookhaven (high salt, 5 weeks) and Rapp (high salt, 6 weeks) animals. Both groups exhibited significant negative correlations between in vivo systolic pressure and maximal responses of mesenteric vessels to norepinephrine and potassium chloride. We suggest that sustained hypertension in Dahl rats has a negative effect on the contractility of the mesenteric arterial system that, by 5 to 6 weeks, masks the initial supersensitivity to norepinephrine. No effects of any diet on the dilating responses of the mesenteric vessels to acetylcholine were observed in any group.

Analysis of the genetic contamination of salt-sensitive Dahl/Rapp rats

Genetic contamination of Dahl/Rapp salt-sensitive rats (SS/JrHsd) was recently discovered in animals received from Harlan Sprague Dawley, Inc, the main supplier of this strain to researchers in the United States. We were interested in determining how this problem occurred and the extent of contamination in the breeding colony in hopes of quickly correcting the problem and reestablishing the supply of this important model of genetic hypertension. DNA was extracted from whole blood obtained from each rat in the Harlan foundation colony and their offspring, the pedigree expansion colony. Several microsatellite-based genetic markers that were polymorphic between the normal and contaminant alleles were used to test these two colonies. All 10 breeder pairs in the foundation colony were tested at six different loci and found to be homozygous for the normal allele in each case. All 60 members of the pedigree expansion colony were also tested, and several rats carrying contaminant alleles were found, thus localizing the origin of the contamination to this colony. We offer several recommendations regarding precautions researchers using inbred animals should take in designing future experiments.

Confirmation of mutant alpha 1 Na,K-ATPase gene and transcript in Dahl salt-sensitive/JR rats

As the sole renal Na,K-ATPase isozyme, the alpha 1 Na,K-ATPase accounts for all active transport of Na+ throughout the nephron. This role in renal Na+ reabsorption and the primacy of the kidney in hypertension pathogenesis make it a logical candidate gene for salt-sensitive genetic hypertension. An adenine (A)1079-->thymine (T) transversion, resulting in the substitution of glutamine276 with leucine and associated with decreased net 86Rb+ (K+) influx, was identified in Dahl salt-sensitive/JR rat kidney alpha 1 Na,K-ATPase cDNA. However, because a Taq polymerase chain reaction amplification-based reanalysis did not detect the mutant T1079 but rather only the wild-type A1079 alpha 1 Na,K-ATPase allele in Dahl salt-sensitive rat genomic DNA, we reexamined alpha 1 Na,K-ATPase sequences using Taq polymerase error-independent amplification-based analyses of genomic DNA (by polymerase allele-specific amplification and ligase chain reaction analysis) and kidney RNA (by mRNA-specific thermostable reverse transcriptase-polymerase chain reaction analysis). We also performed modified 3' mismatched correction analysis of genomic DNA using an exonuclease-positive thermostable DNA polymerase. All the confirmatory test results were concordant, confirming the A1079-->T transversion in the Dahl salt-sensitive alpha 1 Na,K-ATPase allele and its transcript, as well as the wild-type A1079 sequence in the Dahl salt-resistant alpha 1 Na,K-ATPase allele and its transcript. Documentation of a consistent Taq polymerase error that selectively substituted A at T1079 (sense strand) was obtained from Taq polymerase chain reaction amplification and subsequent cycle sequencing of reconfirmed known Dahl salt-sensitive/JR rat mutant T1079 alpha 1 cDNA M13 subclones. This Taq polymerase error results in the reversion of mutant sequence back to the wild-type alpha 1 Na,K-ATPase sequence. This identifies a site- and nucleotide-specific Taq polymerase misincorporation, suggesting that a structural basis might underlie a predisposition to nonrandom Taq polymerase errors.

Evidence for genetic contamination of inbred buffalo rats (RT-1b) obtained from a commercial vendor

Inbred Buffalo rats (RT-1b) have been used in studies of experimental autoimmune encephalomyelitis and autoimmune thyroiditis. Since our studies, and those of others, have relied on the genetic purity of inbred Buffalo rats, we chose to test these animals for expression of strain-dependent, allotype-specific variants of CD45 (leukocyte common antigen, LCA) using the monoclonal antibodies RT7.1 and RT7.2. The goal of this study was to confirm the genetic purity and to verify the inbred status of Buffalo rats obtained from a commercial source.