Effect of Dietary Doses of Quercetin on Hepatic Drug Metabolizing Enzymes in Spontaneously Hypertensive Rats.

BACKGROUND: Administration of quercetin (QR) has shown several health benefits in clinical and pre-clinical studies. OBJECTIVE: This study investigates the effect of dietary doses of QR on hepatic drug metabolizing enzymes in spontaneously hypertensive rats in order to investigate the potential for herb-drug interactions. METHODS: The activity and/or protein expression of selected cytochrome P450 (CYP) enzymes and microsomal epoxide hydrolase were measured in hepatic microsomes using specific probe substrates and/or polyclonal antibodies. Cytosolic fraction was utilized to measure protein level and activity of major antioxidant systems. RESULTS: The doses employed in our study did not cause any significant alterations in the activity and/or protein level of CYP1A1, CYP2A6, CYP2E, and glutathione (GSH). While the activity and apoprotein levels of CYP1A2 and CYP2B1/2 were significantly reduced by the medium and high doses of QR, the activity and/or protein level of microsomal CYP3A and cytosolic GSH-S-transferase, GSH reductase, and GSH peroxidase were significantly enhanced. Activity and protein level of CYP2C9 were significantly inhibited by all doses. Only the high-dose QR resulted in significant inhibition of both microsomal and soluble epoxide hydrolase as well as induction of the antioxidant enzymes, catalase and superoxide dismutase. CONCLUSION: This study demonstrates that dietary doses of QR may offer chemoprevention through stimulation of the endogenous antioxidant systems and inhibition of CYP enzymes involved in bioactivation of procarcinogens. However, modulation of drug metabolizing enzymes by QR could have potential for herb-drug interactions with the possibility of serious complications.

Contribution of independent and pleiotropic genetic effects in the metabolic syndrome in a hypertensive rat.

Hypertension is a major risk factor for cardiovascular disease, Type 2 diabetes, and end organ failure, and is often found concomitant with disorders characteristic of the Metabolic Syndrome (MetS), including obesity, dyslipidemia, and insulin resistance. While the associated features often occur together, the pathway(s) or mechanism(s) linking hypertension in MetS are not well understood. Previous work determined that genetic variation on rat chromosome 17 (RNO17) contributes to several MetS-defining traits (including hypertension, obesity, and dyslipidemia) in the Lyon Hypertensive (LH) rat, a genetically determined MetS model. We hypothesized that at least some of the traits on RNO17 are controlled by a single gene with pleiotropic effects. To address this hypothesis, consomic and congenic strains were developed, whereby a defined fragment of RNO17 from the LH rat was substituted with the control Lyon Normotensive (LN) rat, and MetS phenotypes were measured in the resultant progeny. Compared to LH rats, LH-17LN consomic rats have significantly reduced body weight, blood pressure, and lipid profiles. A congenic strain (LH-17LNc), with a substituted fragment at the distal end of RNO17 (17q12.3; 74-97 Mb; rn4 assembly), showed differences from the LH rat in blood pressure and serum total cholesterol and triglycerides. Interestingly, there was no difference in body weight between the LH-17LNc and the parental LH rat. These data indicate that blood pressure and serum lipids are regulated by a gene(s) in the distal congenic interval, and could be due to pleiotropy. The data also indicate that body weight is not determined by the same gene(s) at this locus. Interestingly, only two small haplotypes spanning a total of approximately 0.5 Mb differ between the LH and LN genomes in the congenic interval. Genes in these haplotypes are strong candidate genes for causing dyslipidemia in the LH rat. Overall, MetS, even in a simplified genetic model such as the LH-17LN rat, is likely due to both independent and pleiotropic gene effects.

The effect of multivitamin-multimineral supplementation on the health status of inbred Wistar and spontaneously hypertensive rat strains.

The nutraceutical industry has proliferated in recent years, with the most popular form of supplementation being the multivitamin-multimineral (MVMM) supplement. In the animal health sector, supplement use has also expanded. The objective of this study was to determine the effects of MVMM supplementation, beneficial or otherwise, on the general health status of the spontaneously hypertensive rat (SHR) strain, an animal model used in hypertension research. A commercially prepared MVMM supplement was given tri-weekly via oral dosing for 8 weeks to two groups of seven adult female SHR and Wistar rats. Their corresponding control groups were dosed with deionised water only. Systolic and diastolic blood pressure, fasting blood glucose, growth rate and food and water intake were measured weekly. At the end of 8 weeks, the animals were euthanased and a full blood profile, urine sodium to potassium ratio, blood urea nitrogen levels and total plasma cholesterol was measured for all groups. The results indicated that growth rate was higher for the SHR supplemented group. Supplementation also decreased diastolic blood pressure in both Wistar and SHR groups and increased red blood cell count and decreased total cholesterol in the SHR group. No adverse effects on the general health status of the animals were observed. MVMM supplementation may therefore be useful in aiding growth and delaying the onset of hypertension and its effects. It may also assist in the longevity of the breeding stock of SHR rats.

Genetic Models in Applied Physiology. HXB/BXH rat recombinant inbred strain platform: a newly enhanced tool for cardiovascular, behavioral, and developmental genetics and genomics.

This review deals with the largest set of rat recombinant inbred (RI) strains and summarizes past and recent accomplishments with this platform for genetic mapping and analyses of divergent and complex traits. This strain, derived by crossing the spontaneously hypertensive rat, SHR/Ola, with a Brown Norway congenic, BN-Lx, carrying polydactyly-luxate syndrome, is referred to as HXB/BXH. The RI strain set has been used for linkage and association studies to identify quantitative trait loci for numerous cardiovascular phenotypes, including arterial pressure, stress-elicited heart rate, and pressor response, and metabolic traits, including insulin resistance, dyslipidemia and glucose handling, and left ventricular hypertrophy. The strain's utility has been enhanced with development of a new framework marker-based map and strain distribution patterns of polymorphic markers. Quantitative trait loci for behavioral traits mapped include loci for startle motor response and habituation, anxiety and locomotion traits associated with elevated plus maze, and conditioned taste aversion. The polydactyly-luxate syndrome Lx mutation has allowed the study of alleles important to limb development and malformation phenotypes as well as teratogens. The RI strains have guided development of numerous congenic strains to test locus assignments and to study the effect of genetic background. Although these strains were originally developed to aid in studies of rat genetic hypertension and morphogenetic abnormalities, this rodent platform has been shown to be equally powerful for a wide spectrum of traits and endophenotypes. These strains provide a ready and available vehicle for many physiological and pharmacological studies.

Determination of percent area density of epithelial and stromal components in development of prostatic hyperplasia in spontaneously hypertensive rats.

OBJECTIVES: To determine the percent area density of epithelial and stromal components in the development of prostatic hyperplasia in spontaneously hypertensive (SH) rats. METHODS: The ventral lobes of prostates obtained from male SH rats and their normotensive counterparts, Wistar Kyoto (WKY) rats, were examined histopathologically at 15, 29, 40, and 54 weeks of age (5 SH and WKY rats each at each age group). The degree of prostatic hyperplasia was evaluated with a score-chart protocol, histoscore. The percent area density of epithelium and stroma of the ventral prostate were determined using a computerized image analysis system. RESULTS: Definite lesions of hyperplastic changes were demonstrated in the ventral prostate of SH rats from 15 to 54 weeks. In comparison with WKY rats, SH rats showed a significantly increased degree of prostatic hyperplasia as reflected by the histoscore values. Furthermore, the histoscore of the ventral prostate of SH rats increased with age (from 21.7 +/- 0.7 at 15 weeks to 26.1 +/- 0.4 at 54 weeks). The percent area density of epithelium and stroma were significantly increased in SH rats, and the ratio of stroma to epithelium ranged from 1:2.94 to 1:3.50 in SH rats but was maintained at 1:1.15 to 1:1.19 in WKY rats during the observation period. CONCLUSIONS: The hyperplastic changes of the ventral prostate may develop with advancing age in SH rats. The development of prostatic hyperplasia may result from both epithelial and stromal proliferation and may be predominantly expressed as a glandular type in SH rats.

Growth characteristics, angiotensin II generation, and microarray-determined gene expression in vascular smooth muscle cells from young spontaneously hypertensive rats.

BACKGROUND: We have demonstrated that vascular smooth muscle cells (VSMCs) derived from spontaneously hypertensive rats (SHR) show exaggerated growth and produce angiotensin (Ang) II and growth factors. These may reflect intrinsic abnormalities in SHR that are not caused by excessive blood pressure, and are associated with genetic abnormalities. OBJECTIVE: To evaluate whether these characteristics of VSMCs from SHR are associated with hypertension or genetic factors. DESIGN AND METHODS: VSMCs were obtained by an explant method from aortas of 4-week-old male SHR/Izumo and Wistar-Kyoto (WKY)/Izumo rats. We evaluated growth characteristics by [3H]thymidine incorporation and cell number increases, immunofluorescence of alpha-smooth muscle (alpha-SM) actin, mRNA expressions of phenotype markers, Ang II-generating system components, and growth factors by reverse transcription and polymerase chain reaction analysis, and Ang II levels by radioimmunoassay in VSMCs. Expression of 850 genes in VSMCs was evaluated by microarray. RESULTS: VSMCs from young SHR showed increased basal DNA synthesis and higher responses of DNA synthesis and cell numbers in response to calf serum. Ang II was significantly increased in conditioned medium and cell extracts from SHR-derived VSMCs than in those from WKY rat-derived VSMCs. mRNA expression of Ang II-generating proteinases, such as cathepsin D and angiotensin-converting enzyme, was greater in VSMCs from SHRs than in cells from WKY rats. Expression of transforming growth factor-beta1, platelet-derived growth factor A-chain and basic fibroblast growth factor mRNAs was greater in VSMCs from SHRs than in cells from WKY rats. Expression of mRNAs of phenotype markers, such as matrix gamma-carboxyglutamic acid (Gla) and osteopontin, was also greater in VSMCs from SHR than in cells from WYK rats. Microarray study showed that VSMCs derived from young SHR increasingly express genes for many enzymes, adhesion molecules and cytokines. CONCLUSION: This study determined that VSMCs derived from young SHR show exaggerated growth, produce Ang II and increasingly express several enzymes, adhesion molecules and cytokines, which are independent of hypertension and possibly associated with genetic abnormalities.

Kynureninase is a novel candidate gene for hypertension in spontaneously hypertensive rats.

The rostral ventrolateral medulla (RVLM) plays a critical role in the tonic and reflexive regulation of arterial blood pressure. Recent studies have demonstrated that injection of kynurenic acid (KYN) into the RVLM of spontaneously hypertensive rats (SHR) decreases arterial blood pressure. We hypothesized that a relative increase in the excitatory amino acid-mediated drive of RVLM vasomotor neurons in SHR may be due to derangement of one of the enzymes that affect the KYN level in the brain. We selected kynureninase, kynureninase hydroxylase, kynurenine aminotransferase type I, and kynurenine aminotransferase type II as candidates that may affect the KYN level in the brainstem. We conducted association studies between polymorphisms of these genes and blood pressure in an F2 population derived from SHR and Wistar-Kyoto rats (WKY). The cosegregation analysis indicated that only the kynureninase gene (KYNU) polymorphism influenced systolic blood pressure (SBP) and residuals of systolic blood pressure after adjusting for heart rate and body weight (RSBP). KYNU was found to be located on rat chromosome 3, and quantitative trait loci analysis at this locus indicated that the logarithms of the odds scores for KYNU in terms of SBP and RSBP were 2.0 and 3.3, respectively. This association with blood pressure decreased in proportion to the distance from KYNU. The expression level of KYNU mRNA in the brainstem was about 3.1 and 2.9 times higher in 10-week-old and 16-week-old SHR than in age-matched WKY, respectively. The increased expression of KYNU in SHR is thought to decrease the KYN level. KYNU seems to be one of the genes that contributes to hypertension in SHR.

Nephron endowment and renal filtration surface area in young spontaneously hypertensive rats.

BACKGROUND/AIMS: A reduction in nephron endowment leading to reduced renal filtration surface area has been implicated in the development of hypertension. The aim of this study was to compare glomerular (and thereby nephron) number and renal filtration surface area in young Wistar-Kyoto rats (WKY) with young spontaneously hypertensive rats (SHR), prior to the development of hypertension in this model. METHODS: Using unbiased stereological methods the number and size of glomeruli, as well as total renal filtration surface area were determined in perfusion-fixed kidneys of 4-week-old WKY and SHR. RESULTS: At 4 weeks of age, in weight-matched animals, there was no significant difference in the number of glomeruli in the kidneys of SHR compared to WKY (28,620 +/- 1,643 and 25,670 +/- 1,263 glomeruli/kidney, respectively). Similarly, there was no difference in mean glomerular volume (SHR: 4.70 +/- 0.31 x 10(-4) mm(3); WKY: 4.28 +/- 0.20 x 10(-4) mm(3)). Surprisingly, total renal filtration surface area was significantly greater in SHR than WKY (3,867 +/- 116 and 3,176 +/- 83 mm(2), respectively). CONCLUSION: The renal abnormality underlying the development of hypertension in the SHR is not due to inborn deficits in nephron endowment and/or filtration surface area.

Decreased endothelial size and connexin expression in rat caudal arteries during hypertension.

OBJECTIVES: Hypertension is accompanied by endothelial dysfunction. The present study has investigated endothelial cell morphology and connexin expression in the caudal artery of the rat during the development of hypertension. METHODS: A significant increase in systolic blood pressure was detected from 9 weeks of age in spontaneously hypertensive male rats (SHR) compared to normotensive Wistar-Kyoto (WKY) rats, reaching a maximum by 11-12 weeks of age. Immunohistochemistry was used to quantify cell size and expression of connexins (Cxs) 37, 40 and 43 in the endothelium of prehypertensive (3-week-old) and hypertensive (12-week-old) rats. RESULTS: At 12 weeks, the size of endothelial cells and the expression of all three Cxs per endothelial cell were significantly less in SHR than WKY rats. At 3 weeks, there was no significant difference in cell size nor in the expression of Cxs 37 or 43; however, expression of Cx40 was significantly lower in SHR than in WKY rats. Between 3 and 12 weeks in WKY rats, there was no change in endothelial cell size, nor in the expression of Cxs 37, 40 and 43. In SHR, both cell size and Cx expression per endothelial cell were significantly decreased during the same developmental period, with a significant decrease in the density of Cx40 plaques. CONCLUSION: The development of hypertension in the SHR is accompanied by significant decreases in endothelial cell size and expression of Cx40, which may contribute to the endothelial dysfunction present in hypertension.

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.

Changes in cardiac energy metabolism during early development of female SHR.

We investigated effects of hypertension and early development on myocardial energy metabolism as reflected by maximal enzyme activities, glucose transporter content, and endogenous substrates in female Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). Left ventricular hypertrophy and systolic hypertension were evident in SHR at 6 weeks of age and these differences increased at 14 and 22 weeks of age. 3-Hydroxyacyl-CoA dehydrogenase (HOAD) activity in the left ventricle was 18% lower in 6-week-old rats than both 14- and 22-week-old rats, but not different between WKY rats and SHR. Hexokinase activity was 15% lower in 6-week-old SHR than WKY rats and decreased progressively with age in both strains. Glucose transporter (GLUT) 1 content was nearly twofold greater in 6-week-old rats than both 14- and 22-week-old rats. We found no difference in citrate synthase activity or GLUT4 content among groups. Glycogen concentration was 44% lower in SHR than WKY rats, whereas triglyceride was slightly (16%) higher in SHR than WKY rats. Older animals had higher levels both glycogen and triglyceride than younger animals. We conclude that the left ventricle of both SHR and WKY rats may change from predominantly glucose to fatty acid oxidation for energy production during early development.

Prolongation of life span in hypertensive rats by dietary interventions. Effects of garlic and linseed oil.

The effects of long-term dietary application of garlic (dried powder, 0.5% in weight of standard chow; G group) or linseed oil (2.5%; L group) as well as a combination of both interventions (L + G group) on the life span of hypertensive rats (SHR SP) was investigated. A further group fed with standard chow served as control (C). The dietary interventions were started at the age of three weeks. Besides regular measurements of the systolic arterial blood pressure (oscillometrically at the tail artery) as well as of heart rate and body weight, autopsy and histological investigations were performed. Both diets, and particularly their combination, prolonged life span significantly (mean values (days) C: 434.5 +/- 23.5; G: 453.2 +/- 16.2; L: 470.0 +/- 26.2; L + G: 494.8 +/- 39.2). There was no significant interaction of the factors garlic and linseed oil. Systolic blood pressure as measured during the compensatory stage (data used until the 39th week of life) was significantly lowered by both garlic (mean -5.8 mm Hg), linseed oil (mean -6.3 mm Hg), and their combination (mean -11.3 mm Hg). The animals died as a consequence of congestive left and right ventricular failure with ventricular hypertrophy, dilatation, myocardial fibrosis and cellular infiltration, left ventricular atrial thrombosis (in most cases), and terminal pneumonia. On the other hand, arteriosclerotic plaques and signs of cerebral stroke could not be detected. Except for the degree of hypertrophy, which was lower in the treated groups, no differences were obvious regarding the morphological findings at the time of death. There was a significant positive correlation between mean blood pressure and the degree of left ventricular hypertrophy. Furthermore, a significant negative correlation between mean blood pressure and ventricular hypertrophy on the one hand and survival on the other hand was obvious provided the total number of animals was considered, however, not within the individual groups. The same applies to the relation between the reduction of left ventricular hypertrophy and life span. The relatively slight hypotensive effect of both dietary interventions as well as the results of previous investigations speaks in favor of a substantial influence of factors independent of blood pressure. In view of controversial results and interpretations in international literature, the mechanisms involved need further study.

Myogenic tone in mesenteric arteries from spontaneously hypertensive rats.

To investigate myogenic tone during the developmental and established phases of hypertension, segments of distal (6th order) mesenteric arteries from spontaneously hypertensive rats (SHR) at 5 and 20 wk were isolated and pressurized in vitro and compared with vessels from age-matched Wistar-Kyoto (WKY) control animals. At 5 wk, tone was significantly enhanced in the SHR. At 20 wk tone was no longer significantly increased over a wide pressure range, although arteries from the SHR were able to maintain diameter at all pressures studied, whereas vessels from the WKY exhibited forced distension at 180 and 200 mmHg. From the relative slope of the pressure-diameter relationship (myogenic index), no increase in peak myogenic responsiveness was observed in arteries from the SHR at either time point. Passive lumen diameters were significantly decreased in arteries from SHR at both time points. From the total and passive midwall circumference-tension relationships, total tension was observed at a reduced midwall circumference in the SHR, but increased absolute levels of total tension were not observed. The normalized midwall circumference-tension relationships in the two strains revealed increased total tension due to active tension development at a reduced normalized circumference at 5 wk in the SHR. At 20 wk the normalized midwall circumference-tension relationships in the two strains were identical. These results demonstrate that myogenic tone in mesenteric arteries is enhanced during the development of hypertension but not when it is established, except at high intraluminal pressures.

Blood pressure and its regulation in spontaneously hypertensive rats bred on the lowest sodium diet for normal growth.

To investigate the effects of dietary sodium restriction from conception to adulthood on blood pressure and its regulatory mechanisms, male offspring were derived from inbreeding in spontaneously hypertensive rats fed a diet containing sodium of 175 mumol/g food (control) or 22 mumol/g (low sodium), which is the least sodium content for normal growth. While urinary sodium excretion was markedly less, the low sodium diet did not inhibit body growth and failed to blunt the development of hypertension. Neither plasma catecholamine concentration nor depressor response to hexamethonium was different between the two groups at any age examined (8, 12, and 20 weeks). Plasma renin concentration was not elevated, whereas urinary excretion of aldosterone was increased at any age in the low sodium group compared with that in the control group. Other sets of rats were fed a diet containing sodium of 175 mumol/g plus mefruside (a diuretic) of 0.001% in the same manner as in the other two groups. Urinary sodium excretion per creatinine was higher than in the other groups. The diuretic treatment inhibited body growth and suppressed adult blood pressure. While the sympathetic function was not affected, both plasma renin concentration and urinary excretion of aldosterone were elevated. These results indicate that dietary sodium restriction with the least sodium for normal growth from conception cannot blunt either the sympathetic nervous function or the development of hypertension in spontaneously hypertensive rats. Aldosterone appears to play an important role in maintaining sodium homeostasis under the dietary sodium restriction.

Developmental regulation of transforming growth factor-beta 1 responses and vascular smooth muscle growth in spontaneously hypertensive rats.

OBJECTIVE: To investigate the developmental regulation of transforming growth factor-beta 1 (TGF-beta 1) action and the expression of TGF-beta receptors in vascular smooth muscle cells (VSMC) isolated from spontaneously hypertensive rats (SHR). DESIGN: TGF-beta 1 effects on proliferation and expression of TGF-beta receptor subtypes were compared in VSMC prepared from SHR, Wistar-Kyoto (WKY) and Sprague-Dawley rats of different ages. METHODS: TGF-beta 1 effects on platelet-derived growth factor-BB (PDGF-BB)-stimulated proliferation were examined in VSMC isolated from SHR, WKY and Sprague-Dawley rats aged 1, 4 and 12 weeks, and from renal hypertensive WKY rats. TGF-beta receptors on the surface of VSMC were identified by affinity labelling, followed by immunoprecipitation with TGF-beta receptor antibodies; complexes were then analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. RESULTS: TGF-beta 1 inhibited by 60-80% PDGF-BB-stimulated proliferation of VSMC from 1-week-old SHR. In 4-week-old SHR, VSMC were resistant to the antiproliferative action of TGF-beta 1, whereas the mitogenic activity of PDGF-BB was increased approximately 150% by TGF-beta 1 in VSMC from 12-week-old SHR. In contrast, TGF-beta 1 inhibited by 10-50% PDGF-BB-stimulated proliferation of VSMC from age-matched WKY and Sprague-Dawley rats. TGF-beta isoforms (TGF-beta 1, -beta 2, -beta 3) all elicited similar growth responses in VSMC from SHR and WKY rats of different ages. Hypertension per se did not alter TGF-beta 1 effects on proliferation, as TGF-beta 1 inhibited by 30-40% growth factor action on VSMC from control, uni-nephrectomized and one-kidney one-clip hypertensive WKY rats. The type I, II and III TGF-beta receptors were expressed on the surface of VSMC isolated from SHR of different ages. CONCLUSION: Alterations in TGF-beta 1 responses, which become evident in VSMC from 4-week-old SHR and are most prominent at 12 weeks, may be important in the development of vascular hypertrophy in this rat strain.

Enhancement of endothelium-dependent relaxation in the aorta from stroke-prone spontaneously hypertensive rats at developmental stages of hypertension.

1. Endothelium-dependent relaxation (EDR) in aortic rings from young (8 weeks) and adult (16 weeks and 20 weeks) stroke-prone spontaneously hypertensive rats (SHRSP) was investigated in comparison with age-matched Wistar-Kyoto rats (WKY). 2. At 8 weeks, acetylcholine (3 x 10(-9)-10(-5) mol/L) and ionomycin (4 x 10(-8)-10(-6) mol/L)-induced EDR in SHRSP aortae was significantly enhanced compared to that in WKY aortae. Mechanical denudation of the endothelium completely abolished, and pretreatment of aortae with NG-monomethyl L-arginine (1 mmol/L), an inhibitor of nitric oxide formation, greatly reduced the relaxation in both strains. Indomethacin (10(-5) mol/L), a cyclo-oxygenase inhibitor that blocks the production of endothelium-derived contracting factors, did not significantly alter the relaxation by acetylcholine at this age. There was no difference in endothelium-independent relaxation of denuded aortae by sodium nitroprusside (10(-9)-10(-6) mol/L) and 8-bromoguanosine 3', 5'-cyclic monophosphate (10(-6)-10(-3) mol/L). 3. In adult SHRSP with established hypertension, however, the acetylcholine (10(-8)-10(-5) mol/L)-induced relaxation markedly diminished at any of the concentrations tested compared to that observed in 8 weeks old SHRSP and WKY at 8-20 weeks of age. This finding differed from other observations where the relaxation in SHRSP was impaired only at higher concentrations of acetylcholine. Indomethacin pretreatment of aortae from 20 week old SHRSP restored acetylcholine-induced EDR to a level comparable with that in age-matched WKY.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative study of various genetic hypertensive rat strains: blood pressure, body weight, growth and organ weights.

In an attempt to compare various genetic strains of hypertensive rats, representative hypertensive strains and associated controls (male, 1-month-old, 6-10 of each strain and 18 strains in total) were collected at a single center (National Institutes of Health; NIH, United States), maintained under the same experimental conditions with normal sodium NIH open formula diet and studied by a single investigator using standard techniques. Animals were measured for blood pressure (BP) by a tail-cuff method without anesthesia and body weight (BW) at 10 and 12 weeks of age and killed to measure organ weights. Hypertension was severe (> 190 mmHg) in spontaneously hypertensive rats (SHR) and their stroke-prone substrains at 12 weeks of age but mild to moderate (145-160 mmHg) in the rest of the hypertensive strains (Dahl's, Milan, Lyon, Sabra, and New Zealand Strains). Regarding organ size, partial correlation analysis showed that organ weights, except for brain and adrenal glands, are good functions of BW and that weight of the left ventricle (LV) was the only one significantly linked to BP levels. A bivariate regression model for LV weight was obtained as follows: LV(mg) = 1.478 BW(g) + 2.13BP(mmHg) - 51(R = 0.878, P < 0.001). The presence of some genetic factor regulating relative organ size independently of BW and BP was suggested in LV weight as well as in the weight of the other organs. Among the strains, MHS was found to be unique for the smallest kidney size and New Zealand strains for the greatest relative LV size when adjusted to allow for the influence of BP.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factor-beta 1 in heart development.

Defined biochemical stimuli regulating neonatal ventricular myocyte (cardiomyocyte) development have not been established. Since cardiomyocytes stop proliferating during the first 3-5 days of age in the rodent, locally generated 'anti-proliferative' and/or differentiation signals can be hypothesized. The transforming growth factor-beta (TGF-beta) family of peptides are multifunctional regulators of proliferation and differentiation of many different cell types. We have determined in neonatal and maturing rat hearts that TGF-beta 1 gene expression occurs in pups of both normotensive (Wistar Kyoto, WKY) and hypertrophy-prone rats (spontaneously hypertensive, SHR). TGF-beta 1 transcript levels were readily apparent in total ventricular RNA from SHR pups within 1 day of age and elevated in 3-7 day old WKY and SHR hearts when cardiomyocyte proliferation indices are diminished. TGF-beta 1 transcript levels remain at a 'relatively' high level throughout maturation and into adulthood in both strains. Further, TGF-beta 1 transcripts were localized to cardiomyocytes of neonatal rat ventricular tissue sections by in situ hybridization. Immunoreactive TGF-beta was co-localized to the intracellular compartment of neonatal cardiomyocytes at the light and electron microscopic level. In vitro analysis using primary cultures of fetal and neonatal cardiomyocytes indicated that TGF-beta s inhibit mitogen stimulated DNA synthesis and thymidine incorporation. From these data, we propose that locally generated TGF-beta s may act as autocrine and/or paracrine regulators of cardiomyocyte proliferation and differentiation as intrinsic components of a multifaceted biochemical regulatory process governing heart development.

Alterations of lymphocyte populations during development in the spontaneously hypertensive rat.

OBJECTIVE: Immune system abnormalities have been linked to hypertension in the spontaneously hypertensive rat (SHR). The goal of our study was to examine different lymphocyte subpopulations in the prehypertensive and developmental phases of hypertension in the SHR. DESIGN: Blood samples were obtained from SHR and Wistar-Kyoto (WKY) rats at the following time-points: 2 weeks and 1, 2, 3 and 4 months. Lymphocytes were separated from the whole blood. METHODS: Monoclonal antibodies were used to fluorescently label the following lymphocyte subpopulations; total T cells, T non-helper cells, T helper cells and B cells. Fluorescence-activated cell sorting (FACS) analysis was used to quantify the percentages of the different subpopulations examined. RESULTS: The T non-helper cell population was depressed in SHR from 2 weeks of age. This finding persisted throughout the entire 4-month study period. At the 4-month time-point, the total T cell percentage was also depressed in the SHR. CONCLUSIONS: These results demonstrate that immune system abnormalities are present in the prehypertensive and developmental phases of hypertension in the SHR. This supports the hypothesis that the immune system is involved in the development and maintenance of hypertension in the SHR, preceding not adapting to this state.