Regulation of multiple renin-angiotensin system genes by Sry

BACKGROUND AND OBJECTIVE

We demonstrated that the Sry gene complex on the spontaneously hypertensive rat (SHR) Y chromosome is a candidate locus for hypertension that accounts for the SHR Y chromosome blood pressure effect. All rat strains examined to date share six Sry loci, and a seventh Sry locus (Sry3) appears to be unique to SHR male rats. Previously, we showed that Sry1 increased activity of the tyrosine hydroxylase promoter in transfected PC12 cells, and Sry1 delivered to adrenal gland of Wistar-Kyoto (WKY) rats increased blood pressure and sympathetic nervous system activity. The objective of this study was to determine whether renin-angiotensin system genes participate in Sry-mediated effects.

METHOD

Sry expression vectors were co-transfected into CHO cells with luciferase reporter constructs containing promoters of angiotensinogen (Agt -1430/+22), renin (Ren -1050/-1), angiotensin-converting enzyme (ACE) (ACE -1677/+21) and ACE2 (ACE2 -1091/+83).

RESULTS

Sry1, Sry2 and Sry3 differentially upregulated activity of the promoters of angiotensinogen, renin and ACE genes and downregulated ACE2 promoter activity. The largest effect was seen with Sry3, which increased activity of angiotensinogen promoter by 1.7-fold, renin promoter by 1.3-fold, ACE promoter by 2.6-fold and decreased activity of ACE2 promoter by 0.5-fold. The effect of Sry1 on promoter activity was significantly less than that of Sry3. Sry2 activated promoters at a significantly lower level than Sry1 did. The result of either an additive effect of Sry regulation of multiple genes in the renin-angiotensin system or alterations in expression of a single gene could favor increased levels of Ang II and decreased levels of Ang-(1-7).

CONCLUSION

These actions of Sry could result in increased blood pressure in males and contribute to sex differences in blood pressure.

Baroreflex gain in normotensive and GH hypertensive rats before and after early gonadectomy

The authors have assessed arterial baroreflex gain in urethane-anesthetized normotensive and New Zealand genetically hypertensive (GH) rats and investigated the effect of gonadectomy in adult animals at 3 weeks of age postnatally. No gender differences in resting blood pressures existed for either normotensive or GH strains. In normotensive animals, bradycardic gain was greater than tachycardic gain and was lower in females than in males. Tachycardic gain was similar in GH and normotensive rats of either sex, but bradycardic gain was lower in GH. Gonadectomy had no effect on baroreflex gain in male or female animals of either strain.

Test- and behavior-specific genetic factors affect WKY hypoactivity in tests of emotionality

Inbred Wistar-Kyoto rats consistently display hypoactivity in tests of emotional behavior. We used them to test the hypothesis that the genetic factors underlying the behavioral decision-making process will vary in different environmental contexts. The contexts used were the open-field test (OFT), a novel environment with no explicit threats present, and the defensive-burying test (DB), a habituated environment into which a threat has been introduced. Rearing, a voluntary behavior was measured in both tests, and our study was the first to look for genetic loci affecting grooming, a relatively automatic, stress-responsive stereotyped behavior. Quantitative trait locus analysis was performed on a population of 486 F2 animals bred from reciprocal inter-crosses. The genetic architectures of DB and OFT rearing, and of DB and OFT grooming, were compared. There were no common loci affecting grooming behavior in both tests. These different contexts produced the stereotyped behavior via different pathways, and genetic factors seem to influence the decision-making pathways and not the expression of the behavior. Three loci were found that affected rearing behavior in both tests. However, in both contexts, other loci had greater effects on the behavior. Our results imply that environmental context's effects on decision-making vary depending on the category of behavior.

No involvement of the nerve growth factor gene locus in hypertension in spontaneously hypertensive rats

Sympathetic hyper-innervation and increased levels of nerve growth factor (NGF), an essential neurotrophic factor for sympathetic neurons, have been observed in the vascular tissues of spontaneously hypertensive rats (SHRs). Such observations have suggested that the pathogenesis of hypertension might involve a qualitative or quantitative abnormality in the NGF protein, resulting from a significant mutation in the gene's promoter or coding region. In the present study, we analyzed the nucleotide sequences of the cis-element of the NGF gene in SHRs, stroke-prone SHRs (SHRSPs), and normotensive Wistar-Kyoto (WKY) rats. The present analyses revealed some differences in the 3-kb promoter region, coding exon, and 3' untranslated region (3'UTR) for the NGF gene among those strains. However, the observed differences did not lead to changes in promoter activity or to amino acid substitution; nor did they represent a link between the 3'UTR mutation of SHRSPs and elevated blood pressure in an F2 generation produced by crossbreeding SHRSPs with WKY rats. These results suggest that the NGF gene locus is not involved in hypertension in SHR/ SHRSP strains. The present study also revealed two differences between SHRs and WKY rats, as found in cultured vascular smooth muscle cells and in mRNA prepared from each strain. First, SHRs had higher expression levels of c-fos and c-jun genes, which encode the component of the AP-1 transcription factor that activates NGF gene transcription. Second, NGF mRNAs prepared from SHRs had a longer 3'UTR than those prepared from WKY rats. Although it remains to be determined whether these events play a role in the hypertension of SHR/SHRSP strains, the present results emphasize the importance of actively searching for aberrant trans-acting factor(s) leading to the enhanced expression of the NGF gene and NGF protein in SHR/SHRSP strains.

Lineage is an epigenetic modifier of QTL influencing behavioral coping with stress

A genome-wide scan was carried out on a segregating F2 population of rats derived from reciprocal intercrosses between two inbred strains of rats, Fisher 344 (F344) and Wistar Kyoto (WKY) that differ significantly in their behavioral coping responses to stress measured by the defensive burying (DB) test. The DB test measures differences in coping strategies by assaying an animal's behavioral response to an immediate threat. We have previously identified three X-linked loci contributing to the phenotypic variance in behavioral coping. Here we report on six significant autosomal quantitative trait loci (QTL) related to different behaviors in the DB test:one for the number of shocks received, three for number of prod approaches, one for latency to bury, and one pleiotropic locus affecting both approach and latency. These QTL contributing to different aspects of coping behaviors show that the effect of genotype on phenotype is highly dependent on lineage. The WKY lineage was particularly influential, with five out of the six QTL affecting coping behavior only in rats of the WKY lineage, and one locus affecting only those in the F344 lineage. Thus, epigenetic factors, primarily of WKY origin, may significantly modulate the genetic contribution to variance in behavioral responses to stress in the DB test.

Quantitative trait loci associated with elevated thyroid-stimulating hormone in the Wistar-Kyoto rat

Thyroid hormones are essential for the regulation of developmental and physiological processes. The genetic factors underlying naturally occurring variability in mammalian thyroid function are, however, only partially understood. Genetic control of thyroid function can be studied with animal models such as the inbred Wistar-Kyoto (WKY) rat strain. Previous studies established that WKY rats have elevated TSH, slightly elevated total T3, and normal total T4 levels compared with Wistar controls. The present study confirmed a persistent 24-h elevation of TSH in WKY rats compared with the Fisher 344 (F344) rat, another inbred strain. Acute T3 challenge (25 microg/100 g body weight ip) suppressed serum TSH and T4 levels in both strains. Quantitative trait locus analysis of elevated TSH in a reciprocally bred WKY x F344 F2 population identified one highly significant locus on chromosome 6 (LOD=11.7, TSH-1) and one suggestive locus on chromosome 5 (LOD=2.3, TSH-2). The confidence interval of TSH-1 contains the TSH receptor and type 2 deiodinase genes, and TSH-2 contains the type 1 deiodinase gene. The WKY alleles of each gene contain sequence alterations, but additional studies are indicated to identify the specific gene or genes responsible for altered regulation of the thyroid axis. These findings suggest that one or more genetic alterations within the TSH-1 locus significantly contribute to the altered thyroid function tests of the WKY rat.

The rat STSL locus: characterization, chromosomal assignment, and genetic variations in sitosterolemic hypertensive rats

BACKGROUND

Elevated plant sterol accumulation has been reported in the spontaneously hypertensive rat (SHR), the stroke-prone spontaneously hypertensive rat (SHRSP) and the Wistar-Kyoto (WKY) rat. Additionally, a blood pressure quantitative trait locus (QTL) has been mapped to rat chromosome 6 in a New Zealand genetically hypertensive rat strain (GH rat). ABCG5 and ABCG8 (encoding sterolin-1 and sterolin-2 respectively) have been shown to be responsible for causing sitosterolemia in humans. These genes are organized in a head-to-head configuration at the STSL locus on human chromosome 2p21.

METHODS

To investigate whether mutations in Abcg5 or Abcg8 exist in SHR, SHRSP, WKY and GH rats, we initiated a systematic search for the genetic variation in coding and non-coding region of Abcg5 and Abcg8 genes in these strains. We isolated the rat cDNAs for these genes and characterized the genomic structure and tissue expression patterns, using standard molecular biology techniques and FISH for chromosomal assignments.

RESULTS

Both rat Abcg5 and Abcg8 genes map to chromosome band 6q12. These genes span ~40 kb and contain 13 exons and 12 introns each, in a pattern identical to that of the STSL loci in mouse and man. Both Abcg5 and Abcg8 were expressed only in liver and intestine. Analyses of DNA from SHR, SHRSP, GH, WKY, Wistar, Wistar King A (WKA) and Brown Norway (BN) rat strains revealed a homozygous G to T substitution at nucleotide 1754, resulting in the coding change Gly583Cys in sterolin-1 only in rats that are both sitosterolemic and hypertensive (SHR, SHRSP and WKY).

CONCLUSIONS

The rat STSL locus maps to chromosome 6q12. A non-synonymous mutation in Abcg5, Gly583Cys, results in sitosterolemia in rat strains that are also hypertensive (WKY, SHR and SHRSP). Those rat strains that are hypertensive, but not sitosterolemic (e.g. GH rat) do not have mutations in Abcg5 or Abcg8. This mutation allows for expression and apparent apical targeting of Abcg5 protein in the intestine. These rat strains may therefore allow us to study the pathophysiological mechanisms involved in the human disease of sitosterolemia.

A missense mutation in the Abcg5 gene causes phytosterolemia in SHR, stroke-prone SHR, and WKY rats

Sitosterolemia is an autosomal recessive disorder caused by mutations in the ABCG5 or ABCG8 half-transporter genes. These mutations disrupt the mechanism that distinguishes between absorbed sterols and is most prominently characterized by hyperabsorption and impaired biliary elimination of dietary plant sterols. Sitosterolemia patients retain 15-20% of dietary plant sterols, whereas normal individuals absorb less than 1-5%. Normotensive Wistar Kyoto inbred (WKY inbred), spontaneously hypertensive rat (SHR), and stroke-prone spontaneously hypertensive rat (SHRSP) strains also display increased absorption and decreased elimination of dietary plant sterols. To determine if the genes responsible for sitosterolemia in humans are also responsible for phytosterolemia in rats, we sequenced the Abcg5 and Abcg8 genes in WKY inbred, SHR, and SHRSP rat strains. All three strains possessed a homozygous guanine-to-thymine transversion in exon 12 of the Abcg5 gene that results in the substitution of a conserved glycine residue for a cysteine amino acid in the extracellular loop between the fifth and sixth membrane-spanning domains of the ATP binding cassette half-transporter, sterolin-1. The identification of this naturally occurring mutation confirms that these rat strains are important animal models of sitosterolemia in which to study the mechanisms of sterol trafficking.

Further dissection of a genomic locus associated with behavioral activity in the Wistar-Kyoto hyperactive rat, an animal model of hyperkinesis

Molecular genetic studies of attention-deficit hyperactivity disorder (ADHD) are a major focus of current research since this syndrome has been shown to be highly heritable.(1) Our approach has been to search for quantitative trait loci (QTL) in a genetic animal model of hyperkinesis, the Wistar-Kyoto hyperactive (WKHA) rat, by a whole-genome scan analysis. In a previous article, we reported the detection of a major QTL associated with behavioral activity in an F2 cross between WKHA and Wistar-Kyoto (WKY) rat strains.(2) Here, we extend our analysis of this cross by adding new genetic markers, now defining a 10 cM interval on rat chromosome 8 associated with ambulatory and exploratory activities. Then we present a replication of this QTL detection, at least for exploratory activity, by a new genetic mapping analysis of an activity QTL in an F2 cross between the WKHA and Brown Norway (BN) rat strains. Overall, the results provide compelling evidence for the presence of gene(s) influencing activity at this locus. The QTL interval has been refined such that the human orthologous region could be defined and tested in human populations for association with ADHD. Ultimately, the improved dissection of this genomic locus should allow the identification of the causal genes.

A new inbred Wistar-Kyoto rat substrain exhibiting apparent salt sensitivity and borderline hypertension

The normotensive Wistar-Kyoto (WKY) rat strain is a traditional control for the spontaneously hypertensive rat (SHR). We found trait differences between two inbred normotensive WKY strains, derived originally from different vendors, and compared these two strains from La Jolla-Taconic Farms (WKY/lj-tf) and La Jolla-Charles River (WKY/lj-cr) with the inbred SHR/lj-cr for cardiovascular, diurnal, and activity traits under normal and high (8%) NaCl diets. Marked genetic diversity was found between the two vendor-derived WKY. By using an extended study design and radiotelemetry, we compared WKY/lj-cr, WKY/lj-tf, and SHR/lj-cr with the following results: systolic pressure (120 +/- 1, 133 +/- 1, 168 +/- 3 mmHg, respectively); diurnal variation in heart rate (DeltaHR: 46 +/- 3, 71 +/- 4, 57 +/- 2 beats/min, respectively); and salt sensitivity of arterial pressure (Deltasystolic: 10 +/- 1, 21 +/- 1, 20 +/- 1 mmHg, respectively). The WKY/lj-tf genotype apparently results in compromised control of arterial pressure and heart rate, especially during high NaCl intake, and greater susceptibility to high pressure (i.e., high NaCl-induced secondary changes). WKY/lj-tf thus constitutes a new inbred borderline hypertensive WKY substrain offering unique opportunities for genomic studies into the development of genetic hypertension.

Difference of gene expression profiles in spontaneous hypertensive rats and Wistar-Kyoto rats from two sources

Spontaneously hypertensive rats (SHR) are a well-known animal model for hypertension. We have previously identified eleven differentially expressed genes in the kidneys between SHR/Hos and Wistar-Kyoto rats (WKY/Hos) using an oligonucleotide microarray and analyzed the correlation between these genes and hypertension. In the present study, we analyzed the differentially expressed genes in the kidneys between SHR/NCrj and WKY/NCrj obtained from an other source to clarify the common and/or specific gene expression between the different sources. Furthermore, expression changes in the representative genes were characterized by Northern blot analysis using samples prepared from a third source, the Izm strain. The comparison revealed quite different changes in the differentially expressed genes among them. Sequence analysis of one of the differentially expressed genes, cytosolic epoxide hydrolase, revealed that two haplotypes could in part explain the expression level. Our study showed the complex nature of the genetic heterogeneity between SHR and WKY from different sources.

Tyrosine hydroxylase gene expression in ventrolateral medulla oblongata of WKY and SHR: a quantitative real-time polymerase chain reaction study

The aims of this study were, first, to determine quantitatively the levels of tyrosine hydroxylase (TH) gene expression in both peripheral and central sites related to blood pressure regulation, and to compare the level of expression in Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). Second, to see if any relationship exists between TH gene expression and systolic arterial blood pressure. Total RNA was isolated from adrenal glands and from tissue punches taken from the C1 and A1 cell groups in the rostral and caudal ventrolateral medulla oblongata of the brainstem, respectively. Total RNA was reverse-transcribed into cDNA followed by quantitative fluorescence detection polymerase chain reaction for TH cDNA. The levels of TH gene expression measured as a percentage of the house-keeping gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH), in SHR, were significantly higher ( approximately 2.5-fold) compared to WKY in all sites examined (P<0.01). There was a positive and significant relationship between systolic blood pressure and TH gene expression in the C1 area of the brainstem in both WKY (n = 5, P<0.05) and SHR (n=6, P<0.05). Taken together, these results suggest that elevated gene expression of the TH gene is associated with the phenotypic characteristic of SHR.

Noradrenergic content and turnover rate in kidney and heart shows gender and strain differences

The objective of this study was to compare strain and gender differences in kidney and heart norepinephrine (NE) content and turnover rate in normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR, SHR/a, and SHR/y). Our laboratory has shown that the Y chromosome has a significant effect on blood pressure in the SHR model of hypertension through the use of two new rat stains, SHR/a and SHR/y, to study the Y chromosome. SHR/a have a SHR autosomal genetic background with a WKY Y chromosome, whereas the SHR/y rats have a WKY autosomal genetic background with a SHR Y chromosome. Tissues were homogenized after alpha-methyl-DL-p-tyrosine injection and analyzed for NE. The male kidney NE content was significantly lower in the WKY compared with the SHR, SHR/y, and SHR/a. Kidney and heart NE content was significantly higher in females compared with males in all strains except the SHR/y. The WKY and SHR/y females had significantly lower kidney NE turnover rates, and the SHR and SHR/a females had significantly higher kidney NE turnover rates than strain-matched males. This study suggests both a strain and gender difference in sympathetic nervous system activity through noradrenergic neurotransmission.

Multiple blood pressure QTL on rat Chromosome 2 defined by congenic Dahl rats

Linkage analysis previously demonstrated a blood pressure quantitative trait locus (QTL) on rat Chromosome 2 (Chr 2) in crosses utilizing Dahl salt-sensitive (S) rats. The present work dissects this QTL by using congenic strains in which segments of Chr 2 from Wistar Kyoto rats (WKY) are placed on the S genetic background. Two distinct QTLs were found where one QTL was anticipated. These each accounted for a blood pressure of 15-20 mm Hg in rats fed 2% NaCl diet for 24 days. One QTL was in the <9-cM interval between D2Rat35 and D2Wox18 (Fgg), and the other was in the <7-cM interval between D2Wox18 (Fgg) and D2Mgh10. A third tentative QTL was suggested, but not clearly established, in the <3-cM interval between D2Mgh10 and D2Rat259.

Contribution of central amiloride-sensitive transport systems to the development of hypertension in spontaneously hypertensive rats

This study was conducted to examine if central amiloride-sensitive transport systems are involved in the development and/or maintenance of hypertension in spontaneously hypertensive rats (SHR). Either amiloride (75 microg/60 microl/day) or artificial cerebrospinal fluid (aCSF, 60 microl/day) was infused centrally (i.c.v.) for 4 weeks to development (4-5-weeks-old) and maintenance (10-12-weeks-old) phases of hypertension in SHR. In development phase, amiloride i.c.v. (n=14) blunted the elevation of blood pressure (BP) compared to aCSF i.c.v. (n=9) (amiloride vs. aCSF; after 3 weeks of i.c.v., 146+/-3 vs. 166+/-5 mmHg, P<0.001). The difference of BP at 3 weeks of i.c.v. was canceled after ganglionic block with hexamethonium (115+/-4 vs. 117+/-5 mmHg). Further, pressor responsiveness to norepinephrine was augmented in amiloride i.c.v. rats (amiloride, n=11 vs. aCSF, n=6; %Delta BP at 800 ng/kg/min.: 16.9+/-1.3 vs. 10.8+/-1.4 mmHg, P<0.05) and this augmentation disappeared after ganglionic block. Pressor responsiveness to angiotensin II and cumulative sodium balance did not differ in the two groups. Intravenous administration of amiloride at the same dose did not attenuate the development of hypertension. On the other hand, in maintenance phase, amiloride i.c.v. by the same protocol as in development phase had no effect on BP in SHR. Also, amiloride i.c.v. did not affect BP in normotensive Wistar-Kyoto rats. These results suggest that central amiloride-sensitive transport systems are involved in the development, but not in the maintenance, of hypertension in SHR through the modulation of autonomic neural mechanisms.

Polymorphisms of the renin gene promoter in spontaneously hypertensive and Wistar-Kyoto rats

1. In the present study, 1.39 kb of the renin gene 5' region in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats was amplified by polymerase chain reaction from genomic DNA and sequenced. Consistent differences in the renin gene sequence of SHR and WKY rats were found at positions -725, -727, -979 and -1126/-1129 as numbered from the transcription start site (+1). No polymorphism was specific to hypertensive rats. 2. Gel-shift assays were performed using labelled SHR renin promotor DNA and nuclear proteins extracted from rat kidneys. The regions between -1122 and -1139 and between -701 and -797 showed protein binding.

Electromechanical alterations in the cerebrovasculature of stroke-prone rats

BACKGROUND AND PURPOSE

Cerebrovascular pressure-dependent constriction (PDC) is associated with smooth muscle (SM) depolarization and Ca(2+) influx through voltage-gated channels. We studied the alterations in electromechanical contraction in the middle cerebral arteries (MCAs) of stroke-prone Wistar-Kyoto spontaneously hypertensive rats (SHRsp) in relation to the stroke-related loss of PDC.

METHODS

Constriction to pressure, elevated [K(+)](o) and/or [Ca(2+)](o), and SM membrane potentials (E(m)) were measured in isolated pressurized MCAs of SHRsp and stroke-resistant SHR.

RESULTS

MCAs of SHRsp exhibited an age-related decrease in PDC before hemorrhagic stroke and a loss of PDC after stroke. At 100 mm Hg, the MCAs of poststroke SHRsp maintained partial constriction that was not altered with pressure but was inhibited by nifedipine (1 micromol/L). The MCAs of poststroke SHRsp constricted to vasopressin (0.17 micromol/L) but not to elevated [K(+)](o). When pressure was reduced from 100 to 0 mm Hg, the MCAs from young prestroke SHRsp exhibited SM hyperpolarization (-38 to -46 mV), whereas those of poststroke SHRsp maintained a constant, depolarized E(m) (-34 mV). Alterations in E(m) with varying [K(+)](o) suggested that there was a decrease in SM K(+) conductance in the MCAs of poststroke SHRsp.

CONCLUSIONS

The observation that the MCAs of poststroke SHRsp depolarize but do not constrict to elevated [K(+)](o) suggests the presence of dysfunctional voltage-gated Ca(2+) channels. The inability to alter E(m) with pressure or to constrict to depolarization could partially contribute to the loss of PDC in the MCAs of poststroke SHRsp.

Sleep in the Wistar-Kyoto rat, a putative genetic animal model for depression

The Wistar-Kyoto (WKY) rat exhibits several behavioral and hormonal abnormalities often associated with depression. One of the hallmarks of depression consists of alterations in the sleep-wake cycle, particularly in rapid eye movement (REM) sleep. If the WKY rat is indeed an animal model for depression, we hypothesized that it should also show sleep abnormalities relative to the control strain, the Wistar (WIS) rat Under baseline conditions, WKY rats showed a 50% increase in total REM sleep time during the 12 h light phase and an increase in sleep fragmentation during both the light and dark phase. The WKY rats also exhibited lower EEG power densities over the entire frequency range (0.2-25.0 Hz) during REM sleep. After a 6 h sleep deprivation, the REM sleep rebound was more pronounced during the dark but not the light phase in the WKY rats. Since the WKY rat represents a genetic model for depression with altered EEG sleep patterns, this strain may be particularly useful for investigating the relationship between depression and sleep abnormalities.

Mapping of four simple sequence repeat (SSR) markers on rat chromosome 4

We previously reported that several markers on rat chromosome (Chr) 4 cosegregated with the occurrence of cerebral stroke and brain edema in stroke-prone spontaneously hypertensive rats (SHRSP). To obtain insights into the positional candidate genes for stroke susceptibility in this region, we mapped four genes, Taurine transporter (Tau), tumor necrosis factor receptor (Tnfr), GABA transporter (Gat1) and glucose transporter-3 (Glut3) genes, using newly developed simple sequence repeat (SSR) markers on rat Chr 4. We isolated the SSRs for the genes either by screening a rat genomic library or by searching the GenBank database. By linkage analysis using two sets of backcrosses, Gat1 and Tnfr were mapped in the region associated with stroke, while Taut was located distant from the region. The Glut3 locus was also assigned to rat Chr 4 using a rat x mouse hybrid clone panel. These results indicated that the Tnfr, Gat1 and Glut3 genes were good positional candidates for the stroke susceptibility in SHRSP, suggesting that further evaluation of these genes by functional studies could prove useful.

Increased nerve growth factor mRNA stability may underlie elevated nerve growth factor secretion from hypertensive vascular smooth muscle cells

Altered nerve growth factor (NGF) regulation has been linked to the pathophysiology of hypertension. Vascular smooth muscle cells from an inbred hypertensive, but normoactive rat strain (WKHT) secreted NGF at a greater rate than from a hyperactive, normotensive strain (WKHA). Exposure to phorbol ester increased NGF secretion rates from WKHT by 400-800% but not from WKHA vascular muscle. NGF secretion rates from both WKHT and WKHA vascular cells were elevated by co-application of platelet-derived growth factor (PDGF) and transforming growth factor-beta1 (TGF-beta1) by 300-1000%. This response was partially attenuated by actinomycin D, an inhibitor of RNA transcription. These results suggest that regulation of NGF production does not occur solely at the level of transcription and post-transcriptional mechanisms operate. Analysis of NGF mRNA stability in the two strains following PDGF and TGF-beta1 treatment showed that NGF mRNA in WKHT had a half-life of 126.2+/-11.68 min while in WKHA vascular smooth muscle cells, the half-life was 47. 33+/-11.98 min. In addition to increased NGF mRNA stability in WKHT vascular muscle, these cells have an increased translational efficiency of NGF protein; elevated synthesis of NGF protein per unit NGF mRNA. Differences in signaling pathways may result in increased NGF mRNA stability and translational efficiency that may account for the elevated NGF protein in WKHT vascular smooth muscle cells.

Genetic differences in morphine sensitivity, tolerance and withdrawal in rats

Significant genetic differences in the endogenous opioid system and in response to a variety of noxious stimuli are present in rodents. We now compared the response to noxious heat with the hot plate test, morphine sensitivity and the development of tolerance and dependence to morphine in spontaneously hypertensive (SHR), Wistar-Kyoto (WK) and Sprague-Dawley (SD) rats. Significant differences were observed in basal nociception among the three strains, where SHRs were hypoalgesic compared to WK and SD. The antinociceptive effect of morphine varied among strains (SD>SHR>WK) as did the rate of tolerance development (10 mg/kg morphine 2/day for 4 days) where WK>SD=SHR. SHR rats developed hyperalgesia following morphine administration during the course of tolerance development. Furthermore, although naloxone (2 mg/kg) precipitated withdrawal symptoms in all tolerant rats, the panorama of symptoms varied among the three strains. Thus, there are significant genetic differences in a variety of effect of opiates.

Mapping of 55 new rat microsatellite markers from chromosome-specific libraries

Fifty-five novel rat microsatellite markers were isolated from libraries specific for rat chromosomes (Chrs) 1, 2, and 7. The markers were mapped in three backcross rat populations. Thirty of these markers mapped to Chrs 1, 2, or 7, while the other 25 mapped to other chromosomes. New markers for two genes, liver-specific transporter gene (Livtr) and insulin-responsive glucose transporter (Glut4), were also mapped to rat Chrs 9 and 10, respectively. Three provisionally assigned markers from previous studies were also confirmed. Detailed methodologies for the generation and enrichment of clones containing repeat sequences and for the isolation of chromosome-specific markers are presented, since they represent unique combinations and modifications of previous protocols. Such methods and the newly presented markers should be useful for both specific and general mapping studies in the rat.

Female Wistar-Kyoto and SHR/y rats have the same genotype but different patterns of expression of renin and angiotensinogen genes

OBJECTIVES

To evaluate whether renin and angiotensinogen gene expression in females from two strains of rats that share the same autosomes and X chromosomes differs. Female SHR/y rats have the parental Wistar-Kyoto rat autosomes and X chromosomes and have no chromosomes of spontaneously hypertensive rat origin; thus they are genetically equivalent to female Wistar-Kyoto rats.

DESIGN AND METHODS

Because these genes are regulated by steroid hormones, we investigated the effects of removal of estrogen (ovariectomy) and addition of androgen (testosterone implants) on three groups of female SHR/y rats and the parental rat strain Wistar-Kyoto rat with groups of intact (control) rats, rats subjected to ovariectomy at age 3 weeks, and rats subjected to ovariectomy with a testosterone implant at age 3 weeks.

RESULTS

The combination of removing estrogen early in development and supplementing the ovariectomized females with testosterone revealed strain differences in response of blood pressure. Renin and angiotensinogen messenger RNA levels appear to be regulated coordinately within each strain, although actual levels of messenger RNA differ between the strains.

CONCLUSIONS

Similar patterns of responses of renin and angiotensinogen genes to ovariectomy and ovariectomy plus testosterone suggest that regulation of the genes is likely to be similar or coordinate. Differences in regulation of renin-angiotensin system genes between strains may result from epigenetic mechanisms such as genome imprinting of these genes or of another gene that functions as a common regulator of renin and angiotensinogen.

Genetic characterization of novel strains of rats derived from crosses between Wistar-Kyoto and spontaneously hypertensive rats, and comparisons with their parental strains

Two novel strains of rats have recently been generated from hybrid crosses of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. The breeding pairs chosen to create these strains were initially selected on the basis of two mutually exclusive phenotypic traits, so that the rats called WKHT are hypertensive but not hyperactive, whereas the rats called WKHA are hyperactive but not hypertensive. These strains have been refined by inbreeding on a strict brother-sister basis for more than 25 generations. To increase usefulness of these strains, we characterized them by use of genetic methods, including DNA finger-printing and simple sequence length polymorphism (SSLP) analyses. We found that these two novel strains are more closely related genetically to either SHR or WKY rats than the degree to which the latter two strains are related to one another; heterozygosities of SSLP marker alleles were extremely rare in WKHA and WKHT, indicating that these strains can be considered as truly inbred (in contrast to WKY rats from two sources); and it was almost always possible to match the SSLP marker alleles found in WKHA and WKHT rats with similarly sized alleles in the parental SHR and WKY alleles, indicating that the WKHA and WKHT strains constitute true mixes of the genomes of SHR and WKY rats. Furthermore, immunogenetic analyses indicated that WKY and WKHT rats belonged to the RT1 l haplotype, whereas SHR and WKHA rats belonged to the k haplotype. These results extend the usefulness of WKHA and WKHT rats for further genetic and physiologic studies.

Angiotensinogen messenger RNA stabilization by angiotensin II

OBJECTIVE

To further characterize the molecular mechanism whereby angiotensin II stabilizes the angiotensinogen messenger (m)RNA through binding studies of the previously isolated polysomal stabilizing protein to partial and mutagenized sequences of the 3' untranslated region of the gene and to explore its importance to rodent genetic hypertension.

DESIGN

Analysis of angiotensinogen mRNA mutants for half-life and binding to a polysomal protein with a molecular weight of 12000.

METHODS

Protein/RNA interactions were determined in band shift assays employing radiolabelled 3' untranslated region of angiotensinogen mRNA. Measurement of the mRNA half-life used a cell-free incubation system and 3' untranslated region DNA sequences were polymerase chain reaction (PCR) cloned and sequenced. Sequences of normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rat (SHR) strains were compared. Point mutations were introduced by site directed mutagenesis.

RESULTS

The angiotensinogen 3' untranslated region exhibited specific binding to the polysomal 12000 molecular weight protein which, in an in vitro incubation system, increased 10-fold the half-life of full-length angiotensinogen mRNA; no effect was observed with 3' deleted angiotensinogen mRNA indicating a regulatory function of protein at the 3' untranslated region. Sequence analysis of PCR amplified DNA fragments identified a (G-->C) point mutation in the La Jolla colony SHR. Following introduction of this point mutation into wild-type 3' untranslated regions, protein binding significantly increased (wild-type binding constant, 19 mumol/l; mutant binding constant 3.5 mumol/l), indicating that this point mutation affects 3' untranslated region secondary structure, binding of the RNA stabilizing protein and, consequently, the half-life of angiotensinogen mRNA. Deletion of a U-rich region (position 1609-1613, UCCUU) expressed twice in the 3' untranslated region almost completely abolished protein binding suggesting this sequence as one part of the putative binding motif in the 3' untranslated region.

CONCLUSIONS

Angiotensin II regulates hepatic angiotensinogen synthesis and secretion by inhibiting degradation of angiotensinogen mRNA by the action of a polysomal protein. Mutations in the 3' untranslated region mRNA coding sequence alter binding and half-life and may significantly affect the half-life of angiotensinogen mRNA thereby altering the secretion rate of angiotensinogen.

Adenosine A1 receptor and its gene expression in ventricles from spontaneously hypertensive rats

We characterized the adenosine A1 receptor and the levels of its mRNA expression in the ventricles of 6- and 13-wk-old Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). The binding of 2-chloro-[3H]cyclopentyladenosine ([3H]CCPA), an A1 agonist ligand, to ventricular membranes was saturable and reversible. The receptor density was significantly lower in SHR than in WKY at 13 wk. The dissociation constant values were not different among these groups. In Northern blot analysis using rat A1 receptor cDNA, levels of mRNA did not differ significantly in the two groups at 13 wk, but the level in SHR significantly exceeded that in WKY at 6 wk. Because plasma adenosine levels were reported to be increased at 13 wk in SHR and we found mRNA levels were similar at this age, the discrepancy between A1 receptor density and its mRNA levels might be related to the desensitization of A1 receptors. Although the implication of this decreased density of A1 receptors is not known, it may involve an increased susceptibility to ischemia.

Angiotensin II regulation of tyrosine hydroxylase gene expression in the neuronal cultures of normotensive and spontaneously hypertensive rats

In the present study we investigated the regulation of tyrosine hydroxylase (TH) by angiotensin II (Ang II) in an attempt to provide cellular and molecular evidence that this hormone has increased neuromodulatory actions in the spontaneously hypertensive (SH) rat brain. Neuronal cells in primary culture from the hypothalamus-brain stem of both normotensive [Wistar-Kyoto (WKY)] and SH rats have been used. These cultures mimic in vivo situations. Ang II caused a time-dependent increase in TH activity in WKY rat brain neurons. A maximal increase of 2.5-fold was observed with 100 nM Ang II in an actinomycin- and cycloheximide-dependent process. In addition, Ang II caused a parallel increase in TH messenger RNA (mRNA) levels, with a maximal stimulation of 5-fold in 4 h by 100 nM Ang II in WKY rat brain neurons. The stimulation of TH mRNA was mediated by the AT1 receptor subtype, resulted from an increase in its transcription, and involved activation of phospholipase C and protein kinase C. Antisense oligonucleotide for c-fos attenuated Ang II stimulation of TH mRNA in a time- and dose-dependent fashion, indicating an involvement of c-fos as a putative third messenger in Ang II stimulation of TH. Ang II also caused stimulation of TH activity and its mRNA levels in neuronal cultures of SH rat brain by a mechanism similar to that observed for neuronal cultures of WKY rat brain, involving AT1 receptors, protein kinase C, and c-fos. However, the stimulation of TH activity and that of TH mRNA were approximately 30% and 80% higher, respectively, in the SH rat brain neurons than those in the WKY rat brain neurons. In vivo experiments have been carried out to validate the elevated response of TH gene expression to Ang II in SH rat brain neuronal cultures. Ang II stimulated both TH activity and TH mRNA levels in the hypothalami and brain stems of adult WKY and SH rats. The level of stimulation in the brain of the SH rat was significantly higher than that in the WKY rat. These observations are consistent with an increase in AT1, receptor gene expression and suggest that increased TH gene expression could be the cellular/molecular basis for the greater neuromodulatory action of Ang II in the SH rat brain.

Alterations in mitochondrial DNA and enzyme activities in hypertrophied myocardium of stroke-prone SHRS

To clarify the pathophysiological alteration of mitochondria in SHRSP hypertrophied heart, mitochondria-related enzyme changes were examined and compared to those in WKY. Furthermore, the structure alteration in mitochondrial DNA (mtDNA) was examined by restriction fragment length polymorphisms (RFLPs). Both isocitrate dehydrogenase (ICDH) and cytochrome c oxidase (COX), which are related to energy production or the respiratory chain in mitochondria, were significantly lower in SHRSP myocardium than in WKY. Furthermore, superoxide dismutase (SOD), a potent radical scavenger, was also lower in SHRSP myocardium. RFLPs analysis by Rsa I revealed two deletions in the electrophoretic band in the SHRSP myocardium, but not in the liver. These findings suggest that mitochondrial dysfunction, especially lower energy production, could be an important factor for the pathogenesis of further myocardial degeneration. The results also suggest that mitochondrial alterations, in the membrane system as well as mtDNA, may be caused by oxidative stress in mitochondria because of decreased scavenging activity.

Cloning, characterization, and genetic mapping of the rat type 2 angiotensin II receptor gene

The renin-angiotensin system plays an important role in blood pressure homeostasis, but the contribution of the type 2 angiotensin II receptor (AT2R) is still unclear. The reports that the AT2R gene has been mapped to the X chromosome in human and rat and the previous report of a gene, Bp3, on the X chromosome responsible for an increase in blood pressure have suggested that the rat AT2R gene (Agtr2) could be this gene. To elucidate whether Agtr2 is Bp3, Agtr2 was cloned. A simple sequence repeat in the 3'-flanking region of this gene was identified and used as a genetic marker to map Agtr2 to the X chromosome at 18.1 cM distal to the androgen receptor locus. This map position is outside the confidence interval reported for Bp3, demonstrating that Agtr2 cannot be Bp3. However, these data will enhance the research into the AT2R biology as well as the study of the X chromosome.

Cloning of the alpha-subunit of GS protein from spontaneously hypertensive rats

Enhanced sodium reabsorption by the kidney has a significant role in the development of genetic hypertension. In the spontaneously hypertensive rat (SHR) model of genetic hypertension, the enhanced sodium reabsorption likely arises from abnormal hormonal regulation of tubular transport. Since hormonal signaling pathways are coupled frequently via GTP binding proteins, one explanation for hormonal abnormalities in SHR would be a defect in a GTP binding protein or proteins. Recent work has suggested that the regulation of Na+,K(+)-ATPase activity by cholera toxin-sensitive GTP binding proteins is abnormal in SHR. The purpose of the present studies was to clone the alpha S-subunit, which is the subunit ADP ribosylated by cholera toxin, of GS protein to determine whether it is abnormal in SHR. Reverse transcription-polymerase chain reaction was able to detect mRNA for alpha S in both Wistar-Kyoto (WKY) rats and SHR. Northern analysis indicated that equivalent amounts of alpha S mRNA were present in WKY rats and SHR. S1 nuclease analysis demonstrated that there was no difference in the amount of alpha S short and long forms between WKY rats and SHR. Subcloning and sequencing of polymerase chain reaction products from WKY rats and SHR indicated that the alpha S forms present in renal cortex were identical. ADP ribosylation studies with cholera toxin demonstrated the presence of equivalent amounts of alpha S protein in WKY rats and SHR. Taken together, these results suggest that the abnormal regulation of Na+,K(+)-ATPase activity by a cholera toxin-sensitive pathway in SHR does not arise from a defect in the alpha S subunit.

Comparison of salt sensitivity of male and female F2 progeny from crosses between WKY and SHRSP rats

1. The present study compared the salt sensitivity of male and female F2 progeny obtained from crosses between Wistar-Kyoto/Izumo rats and stroke-prone spontaneously hypertensive rats (SHRSP A3b/Izm) after salt loading for 7 months. 2. Average systolic blood pressure in male F2 progeny was 10 mmHg higher than that of female F2 progeny at 5 months without salt loading. 3. The blood pressure in male F2 progeny was raised significantly 2 months after salt loading, but there was no further significant change in blood pressure even though salt loading was continued for 5 months. 4. In female F2 progeny, however, a significant change in systolic blood pressure was observed 1 month after salt loading and there was a further significant rise in blood pressure over 6 months. 5. Angiotensin I-converting enzyme and RR1023 loci were strongly linked to systolic and diastolic blood pressures in the male but not the female F2 progeny after salt loading for 7 months. 6. We therefore speculate that the hormonal difference between sexes might influence salt sensitivity in the SHRSP.

Cosegregation of the renin gene with an increase in mean arterial blood pressure in the F2 rats of SHR-WKY cross

Using the restriction endonuclease, BgI I, Samani et al. found a restriction fragment length polymorphism (RFLP) for the renin gene in spontaneously hypertensive rats (SHR) and its normotensive control Wistar-Kyoto (WKY) rats. This RFLP was confirmed in our laboratory in SHR and WKY rats using a rat renin cDNA probe. The correlation of blood pressure and the renin RFLP was examined in 106 F2 rats produced from F1 rats, the offspring of a cross between SHR males and WKY females. Systolic blood pressure was measured by the tail cuff method at 12 weeks of age. Mean arterial blood pressure of anesthetized rats was measured by cannulation of the femoral artery prior to sacrifice. The frequency of renin genotype showed a typical 1:2:1 Mendelian ratio in F2 rats of SHR and WKY cross. The mean arterial blood pressure of F2 rats homozygous with the SHR allele was significantly higher than F2 rats that were heterozygous or homozygous for the WKY allele. No significant difference in systolic blood pressure was observed in these F2 rats. Thus, the renin gene RFLP cosegregates with an increase in mean arterial blood pressure in the F2 rats of SHR and WKY cross.

Distribution of kallikrein-binding protein mRNA in kidneys and difference between SHR and WKY rats

We investigated kallikrein-binding protein (KBP) mRNA distribution in the kidney of Sprague-Dawley (SD) rats, spontaneously hypertensive rats (SHR), and Wistar-Kyoto strain (WKY) rats. Northern blot analysis revealed that KBP mRNA was located mainly in the medulla and with lower amounts in SHR than in WKY rats. KBP mRNA in microdissected nephron segments was detected by reverse transcription and polymerase chain reaction (RT-PCR) followed by Southern blot analysis. In SD rats, the most abundant signals were consistently found in inner medullary collecting duct (IMCD), with small amounts in outer medullary collecting duct, proximal convoluted tubule, and glomerulus. No signals were found in connecting tubule and cortical collecting duct. The nephron distribution of KBP mRNA was similar in WKY and SD rats. Only a small amount of signal was found, however, in IMCD of SHR. In conclusion, 1) KBP mRNA was predominantly distributed in the medullary segments of the distal nephron, downstream from the known kallikrein activity site in the collecting duct, and 2) KBP mRNA expression was significantly decreased in the kidney of SHR.

The rat SA gene shows genotype-dependent tissue-specific expression

1. SA is a recently identified gene implicated in blood pressure regulation in rodent models of genetic hypertension. In this study we have examined, by Northern blotting, its expression in tissues of the spontaneously hypertensive rat, the Wistar-Kyoto rat and F2 rats, derived from a cross of the spontaneously hypertensive rat with the Wistar-Kyoto rat. 2. We demonstrate that the gene is expressed in a tissue-specific manner. Expression was detected in four sites: kidney, liver, brain and testes. 3. In the kidney and liver expression was higher in the spontaneously hypertensive rat than in the Wistar-Kyoto rat, whereas in the brain and testes the pattern was reversed. 4. In the F2 rats, the levels of SA mRNA in the liver, brain and testes were found to be primarily determined by the genotype at the SA gene locus. 5. The findings suggest the presence of strain-specific cis- and more than one tissue-specific trans-acting factors regulating the expression of the rat SA gene.

A new restriction fragment length polymorphism in the first intron of the spontaneously hypertensive rat renin gene

1. Amplification of the entire first intron of the renin gene of spontaneously hypertensive rat (SHR), Wistar-Kyoto (WKY) and Sprague-Dawley rats (SD) followed by Bgl II digestion uncovered a new deletion (approximately 50 bp) which exists upstream of the SHR renin gene first intron tandem repeat element. 2. The SHR tandem repeat element was 600 bp shorter than that in the WKY while the WKY tandem repeat element was 280 bp shorter than that in the SD. 3. Since elements regulating gene expression are known to exist in the first intron of other genes, this new restriction fragment length polymorphism (RFLP) might play a role in the reported overexpression of the SHR renin gene independent of changes in the length of the tandem repeat element.

Angiotensin converting enzyme and genetic hypertension: cloning of rat cDNAs and characterization of the enzyme

Using genetic mapping approaches, a gene on chromosome 10, Bp1, has been identified in the stroke-prone spontaneously hypertensive rat (SHRSP) in the same region that contains the gene for angiotensin converting enzyme (ACE). Since ACE plays an important role in blood pressure regulation, the ACE gene is a leading candidate for Bp1. To examine the possibility that a structural abnormality of ACE exists in the SHRSP, we cloned and characterized the cDNAs for the Wistar-Kyoto rat (WKY) and SHRSP ACE. Both cDNAs encode a single polypeptide of 1,313 amino acid residues with an estimated molecular weight of 150.9 KDa. Five nucleotide differences were identified between the WKY and the SHRSP ACE cDNAs. One of these differences resulted in an amino acid substitution (Lys-207 in the WKY to Arg-207 in the SHRSP). But the enzymatic properties of partially purified ACE from the two strains were similar. Thus the data suggest that an alteration in the primary structure of rat ACE does not contribute to the hypertension in the SHRSP.

Chromosomal mapping of genetic locus associated with thymus-size enlargement in BUF/Mna rats

The thymoma-prone rat of the BUF/Mna strain is a useful model for human thymoma. In this strain thymoma development is regulated by a single autosomal susceptible gene, Tsr-1. At pre-thymoma age, BUF/Mna rats have extremely large thymuses, when compared to those of other strains of rats. Genetic studies in crosses between BUF/Mna rats with large thymuses and WKY/NCrj rats with small thymuses suggested the presence of a major autosomal gene, Ten-1, which contributes to thymus enlargement in a backcross population. Linkage studies between Ten-1 and microsatellite markers in backcross rats of (WKY/NCrj x BUF/Mna)F1 x BUF/Mna have led to the localization of Ten-1 in chromosome 1. This result may provide an approach to clone Tsr-1, which could be allelic to Ten-1.

[Cosegregation studies in spontaneously hypertensive rats]

SHR (spontaneously hypertensive rat) is the most popular genetic hypertensive model rat. Using the F2 progeny obtained from SHR and normotensive rats, for example, WKY (Wistar-Kyoto rat), many cosegregation studies to find the genes responsible for blood pressure have been done. In this review, we present some studies using F2 rats concerning candidate genes, renin, kallikrein, sodium potassium-ATPase, heat shock protein 70, angiotensin converting enzyme, phospholipase C-delta 1 and SA gene to show whether these genes really associate with blood pressure. We discuss the signification of these genes in the process of producing SHR and stroke-prone SHR from WKY. We hope these studies will lead to identify the mechanism of human essential hypertension.

The hypertensive Y chromosome elevates blood pressure in F11 normotensive rats

Our laboratory has shown that the Y chromosome has a significant effect on blood pressure in the spontaneously hypertensive rat (SHR) model of hypertension and that the testes and androgen receptor contribute to the blood pressure rise. As an extension of our research, we have developed two new rat strains, SHR/a and SHR/y (F11) to study the Y chromosome. The objectives of the following research were 1) to study the blood pressure of rats with an SHR Y chromosome in a normotensive genetic background (SHR/y) or a normotensive Y chromosome in an SHR genetic background (SHR/a), 2) to determine the effect of male sex phenotype on the blood pressure of these rats, 3) to determine if testosterone replacement in castrated rats would restore blood pressure, and 4) to determine whether the Y chromosome from the SHR/y strain when crossed with a normotensive female can induce hypertension in androgen receptor-deficient male offspring. Blood pressure of male SHR/y rats was significantly higher than that of normotensive Wistar-Kyoto males (p < 0.01), and SHR/a males had significantly lower blood pressure compared with that of the parent SHR strain (p = 0.05). Testosterone replacement in castrated rats of both strains (SHR/a and SHR/y) restored blood pressure to control levels. Normotensive female King-Holtzman rats heterozygous for the testicular feminization gene were crossed with F11 SHR/a and SHR/y males.(ABSTRACT TRUNCATED AT 250 WORDS)

Sarcoplasmic reticulum calcium transport and Ca(2+)-ATPase gene expression in thoracic and abdominal aortas of normotensive and spontaneously hypertensive rats

Increased intracellular Ca2+ concentration has been associated with the elevation of vascular tone in hypertensive animals. The increase in free cytosolic Ca2+ may partially result from a reduced activity of the sarcoplasmic reticulum (SR) calcium pump. Accordingly we investigated the Ca2+ transport function and the expression of the Ca(2+)-ATPase gene in thoracic and abdominal aortas of normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). Total SR Ca2+ pump activity was estimated by measuring the oxalate-stimulated Ca2+ transport rate on crude homogenates. Ca2+ transport was also measured on highly active microsomal fractions. Our data indicate that the Ca2+ uptake rate, expressed per mg of protein or per g of muscle, is greater in homogenates from aortas of SHR when compared with that of WKY rats. In microsomal fractions isolated from thoracic aortas of SHR compared with WKY rats, the activity and density of SR Ca2+ pump were only slightly increased. The SR Ca2+ transport rate and the amount of each SR Ca(2+)-ATPase mRNA isoform, i.e. SERCA 2a and SERCA 2b, normalized to 18 S ribosomal RNA, were greater in thoracic than in abdominal aorta in both strains. When compared with WKY rats, the level of each SERCA mRNA isoform is higher in the abdominal aorta of SHR but appears similar in the thoracic aorta. Thus, in contrast to previously published data that documented a depressed SR Ca2+ transport activity in the aorta of SHR, the present data indicate that the SR function is increased. These changes in SR activity are accompanied by quantitative changes in expression of the SR Ca(2+)-ATPase gene without alterations in the SR Ca(2+)-ATPase mRNA isoforms pattern.

Organ specificity of the dopamine1 receptor/adenylyl cyclase coupling defect in spontaneously hypertensive rats

The coupling between the dopamine1 (DA1) receptor and the G protein/adenylyl cyclase (AC) enzyme complex is defective in the proximal convoluted tubule (PCT) of 20-wk-old spontaneously hypertensive rats (SHRs). Because this coupling defect could have been due to desensitization secondary to elevated renal dopamine levels in the adult animal, we studied the interaction between DA1 receptors and AC in PCT of rats as early as 3 wk of age, a time when renal dopamine levels are similar in SHRs and their normotensive controls (Wistar-Kyoto rats, WKYs). Maximum receptor density did not change with age and was similar in WKYs and SHRs in all the age groups studied (3, 8, and 20 wk). Basal-, forskolin-, and guanyl nucleotide-stimulated AC activities were also similar in WKYs and SHRs and did not change with age. However, the DA1 agonist-stimulated AC activity was greater in WKYs than in SHRs and increased with age in WKYs but not in SHRs. Moreover, the ability of a nonhydrolyzable analogue of GTP, Gpp(NH)p, to enhance DA1 agonist (SND-919-C12, 1 microM)-stimulated AC activity increased with age in WKY but not in SHRs. To determine if the defect noted in the PCT of SHRs is due to a defective D1A receptor gene, parallel studies were performed in the striatum, since this receptor is expressed predominantly in the latter tissue. In contrast to the results in PCT, radioligand binding and AC studies in striatum revealed no differences between WKYs and SHRs.(ABSTRACT TRUNCATED AT 250 WORDS)

Non convulsive spike-wave discharges do not induce Fos in cerebro-cortical neurons

Immunohistochemical localisation of Fos was used as a marker of neuronal activity to demonstrate neurons active during non-convulsive spike-wave epilepsy. Fos-positive neurons in cortex and several subcortical areas were counted. In undisturbed animals. Fos counts were not related to spike-wave in any region. With the electroencephalographic (EEG) recording procedure. Fos induction occurred in all regions, even after habituation. However, in central cortex, counts were found to be inversely related to spike-wave duration. This suggests that neuronal activity is not increased during spike-wave and that the central cortex in these animals is less responsive to arousal than in non-epileptic animals.

A new genetic locus cosegregating with blood pressure in F2 progeny obtained from stroke-prone spontaneously hypertensive rats and Wistar-Kyoto rats

BACKGROUND

Segregation studies using genomic polymorphisms on F2 progeny obtained from hypertensive rat models showed that a putative hypertensive gene is located close to the angiotensin converting enzyme (ACE) gene. However, it was suggested that additional major genes should contribute to the pathogenesis of hypertension.

METHODS

F2 rats were obtained from stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats of Izumo colony. Blood pressure was measured with a photoelectronic oscillometric tail-cuff method before and during salt loading. Genomic DNA was extracted from livers and digested with HaeIII or Rsal. DNA fingerprinting was performed with 26 32P-labelled human variable number of tandem repeats markers.

RESULTS

Eighty-seven fingerprint bands polymorphic between SHRSP and WKY were obtained. When the distribution of these bands in the F2 progeny was studied, one fingerprint band (1/MCT96.1) showed a distorted distribution between the high- and low-blood pressure subpopulations of the F2 rats, suggesting that the band cosegregated with blood pressure. When blood pressure was compared between the F2 rats with [(+) rats] and without [(-) rats] the 1/MCT96.1 band, it was found that (-) rats had significantly higher basal and salt-loaded blood pressures than (+) rats. The 1/MCT96.1 locus was also shown to have no positive linkage with the ACE locus.

CONCLUSION

The present study showed that examination of the allele distribution between subpopulations with extreme phenotype can be used in the screening of loci cosegregating with blood pressure. Furthermore, a locus not in the ACE region, showing cosegregation with blood pressure in F2 progeny from SHRSP and WKY rats, was found.

Molecular genetics of the SA-gene: cosegregation with hypertension and mapping to rat chromosome 1

OBJECTIVES

The SA-gene shows markedly higher levels of expression in the kidneys of spontaneously hypertensive rats (SHR) than in their non-hypertensive reference strain, the Wistar-Kyoto (WKY) rat. Based on the important role of the kidney in blood pressure regulation, the possibility has been raised that this gene, the translational product of which remains unknown, may participate in the pathogenesis of primary hypertension. The present study was conducted to test this hypothesis and to ascertain the chromosomal localization of the SA-gene.

DESIGN

A cosegregation study was performed using an F2 intercross between stroke-prone SHR (SHRSP) and WKY rats, and a previously described restriction fragment length polymorphism of the SA-gene for characterization of genotype. Mapping of the SA-gene was accomplished by screening a somatic cell-hybrid panel and by linkage group analysis.

RESULTS

A statistically significant difference in systolic blood pressure was found after sodium loading, but not under basal conditions between groups of rats defined by zygosity at the SA locus, consistent with a hypertensive effect of the SHRSP allele. No effect of SA genotype on diastolic blood pressure was observed. The SA-gene was localized on rat chromosome 1.

CONCLUSIONS

This study establishes the SA locus on chromosome 1 as a region in which a gene or genes contributing to blood pressure regulation in this model are localized, and provides further evidence for a possible role of the SA-gene in the pathogenesis of hypertension.

Further evidence of the SA gene as a candidate gene contributing to the hypertension in spontaneously hypertensive rat

We have recently reported that the allele of the SA gene of the Spontaneously hypertensive rat (SHR) has a capacity to influence blood pressure in a F2 rat population prepared from SHR and Wistar-Kyoto rat. In the present study, we have undertaken a similar genetic co-segregation analysis of the F2 rat population prepared from SHR and Lewis rat. The result indicated that, although overall effects of the SA gene genotypes on blood pressure were not significant, a correlation of the genotypes of the SA gene with blood pressure was significantly observed in the female rats of this population. The present results further strengthen our hypothesis that the SA gene, or a gene closely linked to this gene, has a capacity to influence blood pressure.

Hypotensive effect associated with a phospholipase C-δ1 gene mutation in the spontaneously hypertensive rat

To identify the genes responsible for blood pressure in the spontaneously hypertensive rat strain, we performed a cosegregation analysis between the genotype and blood pressure in a set of male F2 rats obtained by crossmating SHR with Wistar-Kyoto rats, a parental normotensive strain. Our investigation revealed that the phospholipase C-delta 1 polymorphism, which resulted in missense mutation, cosegregates with the lower blood pressure in SHR, and that PLC-delta 1 gene is located on chromosome 8. On the other hand, we found the lack of cosegregation between blood pressure and the nerve growth factor receptor gene, which is linked to a hypertensinogenic gene locus (denoted as BP/SP-1) on chromosome 10. We propose that PLC-delta 1 gene itself of closely linked gene on chromosome 8 is a new candidate with the hypotensive effect, and that BP-SP1 locus does not directly contribute to blood pressure elevation in original SHR.