Enhanced DNA synthesis in heart and kidney of newborn spontaneously hypertensive rats

Antihypertensive Effect of Milk Fermented by Lactiplantibacillus plantarum K79 on Spontaneously Hypertensive Rats

The aim of this study is to investigate whether milk fermented by Lactiplantibacillus plantarum K79, which exhibits angiotensin-converting enzyme inhibitory activity, has an effect on lowering the blood pressure of hypertensive rats and to investigate biomarker changes in their blood. Experimental group: normal group (NG, Wistar-Kyoto rats): distilled water, control group [NCG, spontaneously hypertensive rats (SHR)]: distilled water, high treatment group (HTG, SHR): 500 mg/kg/day, medium treatment group (SHR): 335 mg/kg/day, low treatment group (SHR): 170 mg/kg/day, positive control group (PCG, SHR): Enalapril, 10 mg/kg/day. The experimental animals used in this study were divided into groups composed of 8 animals. In terms of weight change, a significant difference was observed between the NG and the SHR group, but there was no significant difference between the SHR group. After 8 wk of feeding, blood pressure was lowered more significantly in the HTG (209.9±13.3 mmHg) than in the NCG (230.8±7.3 mmHg). The treatment group has an effect of lowering blood pressure by significantly suppressing blood pressure-related biomarker protein expression than NG. The results obtained can be used as an antihypertensive material in a variety of food raw materials.

The role of complement in arterial hypertension and hypertensive end organ damage

Increasing evidence indicates that hypertension and hypertensive end organ damage are not only mediated by haemodynamic injury but that inflammation also plays an important role. The complement system protects the host from a hostile microbial environment and maintains tissue and cell integrity through the elimination of altered or dead cells. As an important effector arm of innate immunity, it plays also central roles in the regulation of adaptive immunity. Thus, complement activation may drive the pathology of hypertension through its effects on innate and adaptive immune responses, aside from direct effects on the vasculature. Recent experimental data strongly support a role for complement in all stages of arterial hypertension. The remarkably similar clinical and histopathological features of malignant nephrosclerosis and atypical haemolytic uraemic syndrome suggest also a role for complement in the development of malignant nephrosclerosis. Here, we review the role of complement in hypertension and hypertensive end organ damage. LINKED ARTICLES: This article is part of a themed issue on Canonical and non-canonical functions of the complement system in health and disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.14/issuetoc.

Increased Complement 3 With Suppression of miR-145 Induces the Synthetic Phenotype in Vascular Smooth Muscle Cells From Spontaneously Hypertensive Rats

Background

We previously reported that vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHRs) show the increased expression of complement 3 (C3) and the synthetic phenotype. We targeted the SHR C3 gene (C3 knockout [C3KO] SHRs) by the zinc finger gene editing method. In the current study, we investigated the mechanisms underlying the increased expression of C3 and the role of endogenous C3 in the synthetic phenotype of SHR VSMCs in comparison to cells from Wistar‐Kyoto (WKY) rats and C3KO SHRs.

Methods and Results

Nonmuscle myosin heavy chain staining of aortas from SHRs at 1 day after birth was stronger in comparison to WKY rats and C3KO SHRs. DNA synthesis in VSMCs from SHRs was significantly higher in comparison to WKY rats and C3KO SHRs. Immunohistochemical staining of renin and liver X receptor α in VSMCs from SHRs was stronger in comparison to WKY rats and C3KO SHRs. The expression of renin, Krüppel‐like factor 5, and liver X receptor α proteins in VSMCs from SHRs was significantly higher in comparison to WKY rats and C3KO SHRs. The expression of synthetic phenotype markers osteopontin, matrix gla, and l‐caldesmon, growth factors transforming growth factor‐β1 and platelet‐derived growth factor‐A, transcription factors Krüppel‐like factor 5 and liver X receptor α, and angiotensinogen mRNAs in VSMCs from SHRs was significantly higher in comparison to WKY rats and C3KO SHRs. The expression of miR‐145 mRNA in VSMCs from SHRs was suppressed in comparison to cells from WKY rats. miR‐145 inhibitor significantly increased the expression of C3 in VSMCs from WKY rats, but not in cells from SHRs.

Conclusions

These findings indicate that the increased C3 with the suppression of miR‐145 induces the synthetic phenotype through Krüppel‐like factor 5 and the activation of the renin‐angiotensin system through liver X receptor α in VSMCs from SHRs.

Role of complement 3a in the growth of mesangial cells from stroke-prone spontaneously hypertensive rats

Vascular smooth muscle cells (VSMCs) derived from spontaneously hypertensive rats (SHR) show exaggerated growth with a synthetic phenotype and angiotensin II (Ang II) production associated with increased production of complement (C3). We hypothesized that C3 is involved in the growth of mesangial cells (MCs) from hypertensive rats. We examined the effects of a C3a receptor inhibitor on proliferation, phenotype and Ang II generation in MCs from stroke prone-spontaneously hypertensive rats (SHR)-SP, SHR and Wistar-Kyoto (WKY) rats. Expression of C3 and C3a receptor were evaluated by immunohistochemical staining of the renal cortex. We examined the effects of the C3a inhibitor, SB290157, on proliferation, the expression of phenotype-marker mRNAs and Ang II production in cells from SHR-SP, SHR and WKY rats. Immunostaining of C3 was stronger in SHR and SHRSP glomeruli. MCs from SHR-SP and SHR abundantly express pre-pro C3 mRNA. SB290157 significantly inhibited basal DNA synthesis and proliferation of MCs from SHR-SP and SHR. Expression of osteopontin mRNA in MCs from SHR-SP and SHR was decreased with SB290157 treatment, whereas MC basal expression of α-SMA mRNA was decreased. SB290157 significantly decreased the production of Ang II in MCs from SHR-SP and SHR. Endogenous C3a promotes exaggerated growth with a synthetic phenotype and the production of Ang II in MCs from SHR-SP and SHR. The C3 and C3a receptor system may primarily be involved in the pathogenesis of renal remodeling in hypertensive rats.

Role of complement 3a in the synthetic phenotype and angiotensin II-production in vascular smooth muscle cells from spontaneously hypertensive rats

Background

Spontaneously hypertensive rats (SHR)-derived vascular smooth muscle cells (VSMCs) show exaggerated growth with a synthetic phenotype and angiotensin II (Ang II)-production. To evaluate the contribution of complement 3 (C3) or C3a toward these abnormalities in SHR, we examined effects of a C3a receptor inhibitor on proliferation, phenotype, and Ang II-production in VSMCs from SHR and Wistar–Kyoto (WKY) rats.

Methods

Expression of pre-pro-C3 messenger RNA (mRNA) and C3 protein was evaluated by reverse transcription-PCR and western blot analyses, and C3a receptor mRNA was evaluated by reverse transcription-PCR analysis in quiescent VSMCs from SHR and WKY rats. We examined the effects of the C3a inhibitor, SB290157, on proliferation and the expression of phenotype-marker and Krueppel-like factor 5 (KLF-5) mRNAs in VSMCs from SHR and WKY rats. We examined effects of C3a receptor inhibitor, SB290157, on Ang II-production in conditioned medium of VSMCs from SHR and WKY rats by a radioimmunoassay.

Results

Expression of pre-pro-C3 mRNA and C3 protein was significantly higher in SHR VSMCs than WKY VSMCs. SB290157 significantly inhibited proliferation of VSMCs from SHR, but not in cells from WKY rats. Relative to WKY VSMCs, SB290157 significantly increased the low expression of SM22α mRNA and decreased the high expression of osteopontin mRNA in SHR VSMCs. SB290157 significantly decreased the high expression of KLF-5 and Ang II-production in VSMCs from SHR, but not in cells from WKY rats.

Conclusions

C3a induces exaggerated growth, a synthetic phenotype and Ang II-production in SHR-derived VSMCs. C3a may be primarily involved in cardiovascular remodeling in hypertension.

Dynamic expression of proteins associated with adventitial remodeling in adventitial fibroblasts from spontaneously hypertensive rats

AIM

To identify proteins that could potentially be involved in adventitial remodeling in vascular adventitial fibroblasts (AFs) from spontaneously hypertensive rats (SHR).

METHODS

AFs were isolated from thoracic aortas of 4-, 8-, 16-, and 24-week-old male SHR and Wistar-Kyoto (WKY) rats and cultured to passage 4. Proteomic differential expression profiles between SHR-AFs and WKY-AFs were investigated using 2-D electrophoresis (2-DE), whereas gel image analysis was processed using Image Master 2D Platinum. Protein spots were identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Expression levels of annexin A1 in AFs and aortas from SHR and WKY rats were detected with Western blotting and immunofluorescence techniques.

RESULTS

In 4-, 8-, 16-, and 24-week-old SHR-AFs, 49, 59, 54, and 69 protein spots were found to have significant differences from the age-matched WKY-AFs. Fourteen spots with the same changes in patterns were analyzed in 4-, 8-, 16-, and 24-week-old SHR-AFs with mass spectrometry. Except for cytoskeleton proteins such as tubulin beta 5, it was found that annexin A1, translation elongation factor Tu, endoplasmic reticulum protein 29 and calcium-binding protein 1 were expressed in vascular AFs and their levels changed significantly in SHR-AFs compared with those in WKY-AFs. A decrease in annexin A1 in SHR-AFs was confirmed with Western blotting and immunofluorescence staining at the cell and tissue levels.

CONCLUSION

The application of proteomic techniques revealed a number of novel proteins involved in adventitial remodeling of AFs from SHR, which provide new mechanisms responsible for the occurrence and development of hypertension and potential targets for influencing vascular remodeling in hypertension.

Fibroblast apoptosis precedes cardiomyocyte mass reduction during left ventricular remodeling in hypertensive rats treated with amlodipine

BACKGROUND

A transient induction of apoptosis accompanies the normalization of left ventricular mass index in spontaneously hypertensive rats (SHR) treated with dihydropyridine calcium-channel blockers. However, the cell type undergoing apoptosis in this model and the temporal correlation with onset cardiac remodeling remain undefined.

METHODS AND RESULTS

SHR were treated either with vehicle or amlodipine (20 mg/kg per day) for 4, 7, 10, 14 or 28 days. Amlodipine stably reduced systolic blood pressure by day 2 (-26 +/- 2%) and stably reduced the left ventricular concentration of atrial natriuretic peptide (ANP) mRNA by approximately 50% as early as day 4, suggesting the early reduction of cardiomyocyte stress. Left ventricular mass index was significantly reduced by day 7 (-4.6 +/- 1.5%), in coordination with reduced DNA content (-23 +/- 2%) and non-cardiomyocyte number (-17 +/- 4%). However, the cardiomyocyte cross-sectional area was reduced only starting from day 14. Caspase-3 cleavage was significantly increased at day 7 only. Ultimately, amlodipine for 28 days induced a slight increase in capillary density without affecting total cardiomyocyte number, while reducing the total number of non-cardiomyocytes down to levels seen in untreated normotensive Wistar-Kyoto rats. Bax to Bcl-2 protein ratios were increased from day 7 to day 28. In situ double labeling by the terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) method (apoptosis) combined with rhodamine-labeled lectin binding (endothelial cell marker) revealed a significant increase (> 3-fold) in TUNEL-positive, lectin-negative non-cardiomyocytes in the interstitium between days 7 and 14.

CONCLUSIONS

Left ventricular remodeling induced by amlodipine in SHR involves selective deletion of excess fibroblasts via apoptosis prior to cardiomyocyte mass reduction, but after attenuation of ANP gene expression.

Role of zinc in regulation of arterial blood pressure and in the etiopathogenesis of arterial hypertension

Increased gastrointestinal absorption and urinary excretion of zinc has been confirmed in experimental and clinical studies on primary arterial hypertension as a result from changes of intracellular and extracellular zinc content. In arterial hypertension, the levels of zinc in serum, lymphocyte, and bone decrease while increasing in heart, erythrocytes, kidney, liver, suprarenal glands and spleen. These changes result in the loss of zinc homeostasis that leads to various degrees of deficiency, not entirely compensated by nutritional factors or increased absorption in the gastrointestinal tract. Loss of zinc homeostasis can be both cause and effect of high blood pressure. In the present review, the role of zinc metabolism changes and its mechanisms in arterial hypertension are discussed.

Regulation of therapeutic apoptosis: a potential target in controlling hypertensive organ damage

Cell growth and survival are potential therapeutic targets for the control of complications associated with hypertension. In most cardiovascular disorders, cardiac fibroblasts and large-vessel smooth muscle cells can replicate and thus contribute to the disease. We propose that cardiovascular hyperplasia may be reversed via therapeutic apoptosis induction with drugs that are safe and already used in the clinic. We first reported that, irrespective of the drug class, those drugs that are able to induce regression of cardiovascular hypertrophy are also able to reverse cardiovascular hyperplasia via apoptosis. Drugs active in this regard include inhibitors of the renin-angiotensin system, calcium channel blockers, and beta-blockers. Moreover, the effects of these drugs on cell survival is not merely secondary to blood pressure reduction. Therapeutic apoptosis in the cardiovascular system of the spontaneously hypertensive rat is characterized by a rapid and transient onset following initiation of antihypertensive treatment. Herein, the induction and termination of therapeutic apoptosis during drug treatment of hypertension will be briefly reviewed and supported by novel data suggesting that reversal of cardiovascular hyperplasia is associated with reduced cell growth and a resistance to further induction of therapeutic apoptosis, as shown in spontaneously hypertensive rats receiving an intermittent regime of nifedipine therapy. We propose that the presence of a cell subpopulation with defective cell cycle regulation may determine organ susceptibility to undergo therapeutic apoptosis.Key words: apoptosis, hypertension, hyperplasia, growth, nifedipine.

Synergistic interaction between enalapril, L-arginine and tetrahydrobiopterin in smooth muscle cell apoptosis and aortic remodeling induction in SHR

Smooth muscle cell (SMC) apoptosis occurs at the onset of enalapril-induced regression of aortic hypertrophy in SHR. A potential mechanism is the correction of endothelial dysfunction (ED) leading to reduced production of reactive oxygen species and enhanced bioavailability of nitric oxide (NO), a potent apoptosis inducer. Stimulants of NO include the precursor L-arginine and the NO synthase cofactor tetrahydrobiopterin (BH(4)), which correct ED in several models. The objective was to examine the relationships between ED and the cell growth/death balance during vascular remodeling induced by enalapril in SHR. SHR, 10-week-old, received enalapril (ENA: 30 mg x kg(-1) x day(-1) p.o.) for 1 or 2 weeks, or a co-treatment of L-arginine (2.0 g x kg(-1) x day(-1) p.o.) and BH(4) (5.4 mg x kg(-1) x day(-1) i.p. twice daily) administered alone (group: LB) or in combination with enalapril (ENA+LB) for 1 week. Controls received vehicle. After 1 week, ED was completely corrected with LB but not affected significantly by ENA, whereas both treatments failed to induce SMC apoptosis or aortic remodeling. The correction of ED and the induction of SMC apoptosis (3.3-fold increase in TUNEL labeling) required 2 weeks of ENA treatment. The combination of LB with ENA for 1 week, however, was additive for the reduction of SMC proliferation, and synergistic for the induction of apoptosis and regression of vascular hypertrophy. These interactions were independent of blood pressure regulation. Our results suggest that the correction of ED is not sufficient to induce SMC apoptosis and vascular remodeling, although it facilitates these responses during enalapril treatment.

Complement 3 is involved in the synthetic phenotype and exaggerated growth of vascular smooth muscle cells from spontaneously hypertensive rats

Vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) show the synthetic phenotype and exaggerated growth in comparison with VSMCs from normotensive Wistar-Kyoto (WKY) rats. We investigated genes associated with the synthetic phenotype and exaggerated growth of VSMCs from SHR by microarray. Expression of 1300 transcripts was evaluated by microarray with total mRNA extracted from mid-layer aortic smooth muscle of 3-week-old SHR/Izumo and WKY/Izumo rats. mRNAs encoding sodium-dependent neurotransmitter transporter, epidermal growth factor precursor, EEF2, leptin receptor long-isoform b, clathrin assembly protein short form, and preprocomplement 3 (pre-pro-C3) were expressed only in aortic smooth muscle from SHR by microarray and by reverse-transcription polymerase chain reaction analysis. Pre-pro-C3 mRNA was detected only in cultured VSMCs from SHR. Exogenous C3 changed VSMCs to the synthetic phenotype. Antisense oligodeoxynucleotides (ODN) to C3 reduced the higher level of DNA synthesis in VSMCs from SHR. Antisense ODN to C3 increased expression of SM22alpha mRNA and decreased expression of osteopontin and matrix Gla mRNAs. It also decreased expression of growth factor mRNAs in VSMCs from SHR. In conclusion, we have shown that C3, independent of other complement molecules, has direct effects on the phenotype of VSMCs and stimulates growth of these cells. C3 is produced only by VSMCs from SHR. Therefore, C3 may be the gene underlying the synthetic phenotype and exaggerated growth of VSMCs from SHR. C3 may be a new target for the treatment of hypertension.

Kinin B2 receptor is not involved in enalapril-induced apoptosis and regression of hypertrophy in spontaneously hypertensive rat aorta: possible role of B1 receptor

1. Treatment with enalapril induces smooth muscle cell apoptosis and regression of aortic hypertrophy in spontaneously hypertensive rats (SHRs), whereas combined blockade of angiotensin II AT(1) and AT(2) receptors does not. We postulated that vascular apoptosis with enalapril involves enhanced half-life of bradykinin (BK) and kinin B(2) receptor stimulation. 2. SHR, 11-weeks old, were treated for 4 weeks with enalapril (30 mg kg(-1) day(-1)), Hoe 140 (500 microg kg(-1) day(-1); B(2) receptor antagonist), alone or in combination. Controls received vehicle. 3. The half-life of hypotensive responses to intra-arterial bolus injections of BK were significantly increased in SHR anesthetized after 4 weeks of enalapril, an effect prevented by Hoe 140. The magnitude of BK-induced hypotension was significantly attenuated in all rats treated with Hoe 140. 4. As compared to placebo, enalapril treatment significantly reduced blood pressure (-34+/-2%), aortic hypertrophy (-20+/-3%), hyperplasia (-37+/-5%) and DNA synthesis (-61+/-8%), while it increased aortic DNA fragmentation by two-fold. Hoe 140 given alone or in combination with enalapril affected none of these parameters. 5. As a possible alternative mechanism, aortae isolated during the second week of enalapril treatment showed a transient upregulation of contractile responses to des-Arg(9)BK (EC(50)<1 nM), which were significantly reduced by [Leu(8)]des-Arg(9)BK (10 microM). Moreover, in vitro receptor autoradiography revealed an increase in expression of B(1) and B(2) receptor binding sites by 8-11 days of enalapril treatment. 6. Aortic apoptosis induction and hypertrophy regression with enalapril do not involve kinin B(2) receptors in SHR. Kinins acting via B(1) receptors remains a candidate mechanism.

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.

Evidence of an altered in vivo vascular cell turnover in spontaneously hypertensive rats and its modulation by long-term antihypertensive treatment

The aims of this study were to measure in vivo cell turnover in the thoracic aorta from spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) and to investigate how it could be modulated by chronic antihypertensive treatment. Cell turnover was estimated in rats in which DNA had been prelabeled in utero with [ 3 H]-thymidine, by the rate of disappearance of total [ 3 H]-DNA from birth to 20 weeks of age. In SHR compared with WKY, neonatal relative aortic mass was transiently elevated and was reversed to hypotrophy at 8 weeks. At 20 weeks of age, aortic hypertrophy reappeared. Aortic DNA content reflected the morphologic changes observed with age. In both SHR and WKY, the decline with time in [ 3 H]-prelabeled aortic DNA coupled with the increase in total organ DNA demonstrated that cells prelabeled in utero died and were replaced. Decline in [ 3 H]-DNA from birth to 8 weeks of age was approximately threefold faster in the aorta from SHR than in WKY. In older SHR, the decrease in [ 3 H]-DNA was then slower and similar to that of WKY. Chronic treatment of SHR for 15 weeks from the age of 5 weeks, with hydralazine, enalapril, or nifedipine prevented the rise in systolic blood pressure, aortic mass, and DNA content. This was associated with an unchanged residual radioactivity of [ 3 H]-prelabeled aortic DNA over time, suggesting that the treatment did not stimulate cumulative cell death. We propose that the altered cell turnover is a component of aortic remodeling observed in hypertension. Our data also suggest that it is possible to modulate in vivo cell turnover and affect vascular remodeling by pharmacologic therapy.

Workshop: excess growth and apoptosis: is hypertension a case of accelerated aging of cardiovascular cells?

Several groups including ours have demonstrated cardiac hyperplasia in neonates from genetically hypertensive rat strains. We have shown that similar problems exist in the kidney as well. More recently, we found that excessive heart and kidney weight is neonatally related to inhibition of apoptosis. Using recombinant inbred strains derived from a reciprocal cross between Brown Norway and spontaneously hypertensive rat progenitor strains, we mapped the inhibition of neonatal apoptosis to 2 distinct loci on chromosomes 1 (Myl 2) and 18 (Abrb 2). Positional candidate genes at these loci are being explored. These studies have also demonstrated that the loci determining kidney and heart weights in neonates are distinct from those determining increased organ weight in adults. The impact of blood pressure per se is also divergent because adult kidney weight is negatively correlated whereas heart weight is positively correlated with it. Analyses by extremes of low and high percentiles from fetal life to adulthood identified a single locus determining heart weight at Acaa on chromosome 8 in newborn (P=0.0003) and adult (P=0.016) rats. The Acaa region contains a DNA mismatch repair gene (hMLH1). The kinetics of neonatal growth through adulthood by prelabeling DNA with [(3)H]thymidine in pregnant mares showed that although the growth process is complex and nonlinear in the kidney of hypertensive rats, there is an increased turnover of cells, that is, reduced half-life of DNA. This observation is supported by the presence of shorter telomere fragments in kidneys of spontaneously hypertensive rats. These studies suggest that cardiovascular cells from hypertensive animals are subject to accelerated turnover, potentially leading to their accelerated aging.

Proapoptotic and growth-inhibitory role of angiotensin II type 2 receptor in vascular smooth muscle cells of spontaneously hypertensive rats in vivo

Angiotensin type 2 (AT(2)) receptors for angiotensin II suppress cell growth and induce apoptosis in vitro, but their role is poorly defined in vivo. We reported that transient induction of smooth muscle cell (SMC) apoptosis precedes DNA synthesis inhibition and aortic hypertrophy regression in spontaneously hypertensive rats treated with the AT(1) antagonist losartan or the converting-enzyme inhibitor enalapril. Although both drugs are equipotent in reducing SMC number, apoptosis occurs significantly earlier with losartan than enalapril. To examine the role of AT(2) receptors in this model, spontaneously hypertensive rats were given valsartan, an AT(1) antagonist, or enalapril, in combination or not with the AT(2) antagonist PD123319 for 1 or 2 weeks. Control rats received vehicle. Systolic blood pressure was reduced similarly by valsartan and enalapril but it was not significantly affected by PD123319. Angiotensin II plasma levels were increased (6-fold) with valsartan and reduced (80%) with enalapril but unaffected by PD123319. Valsartan significantly increased internucleosomal DNA fragmentation indicative of apoptosis at 1 week only (2.7-fold) and significantly reduced aortic mass (18%), SMC number (33%), and DNA synthesis (24%, measured by (3)H-thymidine incorporation) at 2 weeks. These valsartan-induced changes were prevented by PD123319. In contrast, enalapril-induced DNA fragmentation (2-fold increase at 2 weeks) was not affected by PD123319. PD123319 given alone did not affect growth or apoptosis. AT(1) and AT(2) receptor mRNAs were detected in the aorta by reverse transcription-polymerase chain reaction. Together, these results provide the first evidence that AT(2) receptors mediate vascular mass regression by stimulating SMC apoptosis in vivo, an effect seen during AT(1) receptor blockade but not during converting-enzyme inhibition.

Apoptosis during regression of cardiac hypertrophy in spontaneously hypertensive rats. Temporal regulation and spatial heterogeneity

We previously reported that increased apoptosis participates in the regression of aortic hypertrophy in spontaneously hypertensive rats. To further document the potential role of apoptosis in cardiovascular therapy, we examined apoptosis during regression of hypertrophy in the heart of spontaneously hypertensive rats receiving the antihypertensive drug enalapril (30 mg. kg(-1). d(-1)), losartan (30 mg. kg(-1). d(-1)), nifedipine (35 mg. kg(-1). d(-1)), hydralazine (40 mg. kg(-1). d(-1)), propranolol (50 mg. kg(-1). d(-1)), or hydrochlorothiazide (75 mg. kg(-1). d(-1)) for 1 to 4 weeks, starting at 10 to 11 weeks of age. Systolic blood pressure and heart rate were measured by the tail-cuff method. Markers of apoptosis included oligonucleosomal DNA fragmentation in extracted cardiac DNA or in situ in ventricular cross sections labeled with terminal deoxynucleotidyl transferase. Cardiac DNA synthesis was evaluated by [(3)H]-thymidine incorporation in vivo. All drugs reduced cardiac workload, defined as the product of blood pressure and heart rate, by >20% at 4 weeks. However, only nifedipine, enalapril, losartan, and propranolol reduced cardiac mass (>19%) within 4 weeks. Regression of cardiac hypertrophy was accompanied by a 50% to 300% increase in DNA fragmentation and a >20% reduction in DNA synthesis, resulting in a >20% reduction in cardiac DNA content after 4 weeks. Apoptosis induction occurred early and was transient within 4 weeks of nifedipine, enalapril, or losartan administration. With all regression-inducing drugs, the increase in DNA fragmentation occurred mainly in the subepicardium. Thus, transient induction of apoptosis in the subepicardium appears to be a characteristic feature of the early response to drug-induced regression of cardiac hypertrophy in spontaneously hypertensive rats.

Production of angiotensin II by homogeneous cultures of vascular smooth muscle cells from spontaneously hypertensive rats

Production of angiotensin II (Ang II) in spontaneously hypertensive rats (SHR)-derived vascular smooth muscle cells (VSMC) has now been investigated. A nonpeptide antagonist (CV-11974) of Ang II type 1 receptors inhibited basal DNA synthesis in VSMC from SHR, but it had no effect on cells from Wistar-Kyoto (WKY) rats. Ang II-like immunoreactivity, determined by radioimmunoassay after HPLC, was readily detected in conditioned medium and extracts of SHR-derived VSMC, whereas it was virtually undetectable in VSMC from WKY rats. Isoproterenol increased the amount of Ang II-like immunoreactivity in conditioned medium and extracts of SHR-derived VSMC, whereas the angiotensin-converting enzyme inhibitor delapril significantly reduced the amount of Ang II-like immunoreactivity in conditioned medium and extracts of these cells. Reverse transcription-polymerase chain reaction analysis revealed that the abundance of mRNAs encoding angiotensinogen, cathepsin D, and angiotensin-converting enzyme was greater in VSMC from SHR than in cells from WKY rats. The abundance of cathepsin D protein by Western blotting was greater in VSMC from SHR than in cells from WKY rats. Ang I-generating and acid protease activities were detected in VSMC from SHR, but not in cells from WKY rats. These results suggest that SHR-derived VSMC generate Ang II with increases in angiotensinogen, cathepsin D, and angiotensin-converting enzyme, which contribute to the basal growth. Production of Ang II by homogeneous cultures of VSMC is considered as a new mechanism of hypertensive vascular disease.

Molecular mechanisms of the exaggerated growth of vascular smooth muscle cells in hypertension

The molecular mechanisms of the exaggerated growth of vascular smooth muscle cells (VSMC) in hypertension are reviewed based on our previous experimental data. Spontaneously hypertensive rats (SHR)-derived VSMC increasingly express angiotensinogen, cathepsin D and angiotensin-converting enzyme (ACE) mRNAs, compared to cells from normotensive Wistar-Kyoto (WKY) rats, indicating the presence of an Ang II generating system in a homogeneous culture of VSMC from SHR. The produced Ang II then induces TGF-beta. SHR-derived VSMC show the distinct expression and abnormal regulation by Ang II of TGF-beta receptors when compared with cells from WKY rats, which express TGF-beta type II receptor predominantly to induce PDGF A-chain stimulation of VSMC growth. These findings imply that the increased growth of VSMC in hypertension is a primary event independent of high blood pressure, and is associated with endogenous Ang II-related growth factors.

Newborn and adult recombinant inbred strains: a tool to search for genetic determinants of target organ damage in hypertension

It has been proposed that one of the primary events in the development of essential hypertension is a growth-related process initiated as early as during fetal development. Differences in kidney size have been observed between most rat models of hypertension and their respective controls. In this study, we analyzed relative kidney size (kidney weight/body wt) in a set of rat recombinant inbred strains (RIS) (N = 27) and their progenitors, the spontaneously hypertensive rat strain (SHR/Ola) and Brown Norway congenic strain (BN.1x), at two different ages, at birth and at 15 weeks. In the progenitors, the relative kidney weight was higher in the hypertensive than in the normotensive strain of both the newborn (P < 0.001) and adult (P < 0.001) animals. In the RIS, a significant correlation was found between the newborn and adult relative kidney weight (r = 0.49, P = 0.01), indicating that the two phenotypes share some of their genetic determinants. A total genome search of newborn and adult relative kidney weight was performed with a total of 453 genetic markers. These analyses revealed several suggestive quantitative trait loci (QTL), some of which were, indeed, significant for both newborn and adult relative kidney weight (such as, D3Mit9 on rat chromosome 3; r = -0.50, P < 0.01; r = -0.47, P < 0.01; respectively). Others, such as the locus on rat chromosome 1 (Rt6; r = -0.43, P < 0.05), were significant only for the adult relative kidney size. This QTL was found in close proximity to a region previously related to susceptibility to hypertensive renal disease in the fawn-hooded rat and, similarly to that study, its effect was found to be independent of blood pressure. Furthermore, a growth pattern of the kidneys after birth, evaluated as the difference between the newborn and adult relative kidney weight, was also subjected to total genome scan. Several suggestive QTL were identified. One of the most significant loci was found at the D1a marker on rat chromosome 17 (r = -0.51, P < 0.01), which was previously related to the determination of adult heart weight in the RIS. In conclusion, the current study demonstrates the usefulness of RIS in studies of hypertension-related phenotypes, some of which are abnormal before the development of high blood pressure. To better understand their role in the pathogenesis of hypertension, studies at different ages are needed, which are uniquely feasible in RIS.

Hypertension: genes and environment

Hypertension can be classified as either Mendelian hypertension or essential hypertension, on the basis of the mode of inheritance. The Mendelian forms of hypertension develop as a result of a single gene defect, and as such are inherited in a simple Mendelian manner. In contrast, essential hypertension occurs as a consequence of a complex interplay of a number of genetic alterations and environmental factors, and therefore does not follow a clear pattern of inheritance, but exhibits familial aggregation of cases. In this review, we discuss recent advances in understanding the pathogenesis of both types of hypertension. We review the causal gene defects identified in several monogenic forms of hypertension, and we discuss their possible relevance to the development of essential hypertension. We describe the current approaches to identifying the genetic determinants of human essential hypertension and rat genetic models of hypertension, and summarise the results obtained to date using these methods. Finally, we discuss the significance of environmental factors, such as stress and diet, in the pathogenesis of hypertension, and we describe their interactions with specific hypertension susceptibility genes.

Early, short-term treatment with captopril permanently attenuates cardiovascular changes in spontaneously hypertensive rats

The purpose of the current study was to determine if early, short-term treatment of spontaneously hypertensive rats (SHR) with captopril would cause a persistent attenuation of the structural alterations of the heart, aorta, and coronary arteries that are commonly seen in adult SHR. Therefore, mating pairs of SHR were treated with captopril and the pups were kept on captopril (SHRC) or were taken off captopril at two months (SHROC). Untreated SHR and Wistar-Kyoto (WKY) rats were mated and served as controls. At 8-10 months of age, heart weight and left ventricular weight/body weight ratios were increased in SHR compared to WKY, SHRC, and SHROC. Aortic medial areas of SHR and SHROC were similar and were larger than WKY and SHRC. Nuclear density in SHR and SHROC was less than WKY and SHRC suggesting hypertrophy of the medial wall. In coronary vessels, medial thickness was greatest in SHR, while there was no difference among WKY, SHRC, SHROC. These data suggest that early, short-term treatment of SHR with captopril permanently attenuated the structural alterations in the heart and coronary vessels that are commonly seen in adult SHR.

Antisense oligodeoxynucleotide complementary to platelet-derived growth factor A-chain messenger RNA inhibits the arterial proliferation in spontaneously hypertensive rats without altering their blood pressures

OBJECTIVE

To evaluate the effects of the antisense oligodeoxynucleotide (ODN) to platelet-derived growth factor (PDGF) A-chain messenger RNA (mRNA) on the growth of cardiovascular organs in hypertension.

DESIGN

15-Mer antisense ODN complementary to the initiation codon region of rat PDGF-A chain mRNA and non-sense ODN of identical proportion but with a random order of bases relative to that of antisense ODN were synthesized with a DNA synthesizer.

METHODS

We examined the effects of the antisense ODN on the growth of vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats, and on the expression of PDGF A-chain mRNA by reverse transcription and polymerase chain reaction and PDGF A-chain protein by Western blot analysis in vitro. We evaluated the distribution of 32P-labeled antisense ODN and examined the effects of the antisense ODN on the growth of cardiovascular organs in vivo.

RESULTS

The antisense ODN reduced the basal DNA synthesis of VSMC from SHR significantly, but did not do so in cells from Wistar-Kyoto rats. Mutations in the antisense ODN sequence reduced the ODN-induced inhibition of DNA synthesis. Addition of serum or transforming growth factor-beta 1 increased the DNA synthesis in the SHR-derived VSMC that was inhibited by the antisense ODN. The antisense ODN inhibited the production of PDGF A-chain protein, but not of the PDGF A-chain mRNA. The injection of 32P-antisense ODN in vivo led to a greater accumulation of radioactivity in the aorta than in other organs. Infusion of antisense ODN for 28 days did not alter the systolic blood pressure appreciably in rats of either strain. However, in SHR, it reduced markedly the elevated DNA content, [3H]-thymidine uptake, and incorporation of [3H]-thymidine into aortic DNA, and suppressed the production of aortic PDGF A-chain protein. These results indicated that the PDGF A-chain is involved in the exaggerated growth of VSMC from SHR by which inhibition of the translation of PDGF A-chain mRNA to the protein with antisense ODN occurs in vitro, and that antisense ODN to PDGF A-chain suppresses the exaggerated arterial proliferation in SHR without altering the high blood pressure in vivo.

CONCLUSION

These results imply that inhibition of the final responsible growth factor PDGF A-chain by antisense ODN can suppress the arterial proliferation in hypertension without altering the blood pressure, suggesting that the arterial proliferation in hypertension is independent of the high blood pressure in part, and that antisense therapy could be feasible for treating hypertension.

Altered balance between cell replication and apoptosis in hearts and kidneys of newborn SHR

Apoptosis is involved in neonatal remodeling of organs of the cardiovascular system. Since we previously reported hyperplasia of these organs at birth in several forms of genetic hypertension, the aim of this study was to determine whether alterations of the apoptotic process could explain our findings. The heart, aorta, and kidneys of newborn Wistar-Kyoto and spontaneously hypertensive rats were harvested 24 hours after an injection of [3H]thymidine. DNA was extracted to measure its specific activity (index of DNA synthesis) and DNA fragmentation as an estimation of apoptosis. All organs studied showed an increased weight to body weight ratio in spontaneously hypertensive rats. Twenty-four hours after birth, DNA synthesis in all organs of spontaneously hypertensive rats was comparable to that in normotensive rats. However, apoptosis was markedly decreased in the heart and kidneys of newborn spontaneously hypertensive rats compared with their normotensive controls. In the aorta, apoptosis was reduced, but not significantly. Calculation of a proliferation index (DNA synthesis/fragmentation) revealed a significant increase of heart proliferation, with a similar trend in the aorta and kidneys. In addition, we found a negative correlation between heart weight and DNA fragmentation. Although other factors may influence hyperplasia of the aorta, we propose that a reduction of apoptotic activity is responsible, at least in part, for heart and kidney hyperplasia in newborn spontaneously hypertensive rats.

Smooth muscle apoptosis during vascular regression in spontaneously hypertensive rats

We previously reported that apoptosis is increased in smooth muscle cells cultured from the aorta of spontaneously hypertensive rats versus normotensive controls. As an initial in vivo exploration, we now examined smooth muscle cell apoptosis regulation during the regression of vascular hypertrophy in the thoracic aorta media of spontaneously hypertensive rats receiving the antihypertensive drug enalapril (30 mg.kg-1.d-1), losartan (30 mg.kg-1.d-1), nifedipine (35 mg.kg-1.d-1), hydralazine (40 mg.kg-1.d-1), propranolol (50 mg.kg-1.d-1), or hydrochlorothiazide (75 mg.kg-1.d-1) for 1 to 4 weeks starting at 10 to 11 weeks of age. Three criteria were used to evaluate smooth muscle cell apoptosis: (1) oligonucleosomal fragmentation of the extracted aortic DNA, (2) reduction in aortic DNA content, and (3) depletion of smooth muscle cells in the arterial media. Arterial DNA synthesis was evaluated by [3H]thymidine incorporation in vivo. After 4 weeks of treatment, systolic blood pressure was reduced significantly by > 42% with losartan, enalapril, and hydralazine, and by 23% with nifedipine, versus control values of 220 +/- 5 mm Hg. However these agents affected vascular growth and apoptosis differently. Losartan, enalapril, and nifedipine stimulated smooth muscle cell apoptosis threefold to fivefold before there was a significant reduction in DNA synthesis (> 25%), vascular mass (> 19%), or vascular DNA content (> 38%), and these treatments markedly reduced (by 38% to 50%) medial cell number as measured at 4 weeks by the three-dimensional disector method. Losartan and nifedipine stimulated smooth muscle cell apoptosis before reducing blood pressure. In contrast, hydralazine did not affect vascular mass, apoptosis, or DNA synthesis, although blood pressure was lowered. Propranolol or hydrochlorothiazide failed to affect hypertension or vascular growth. Thus, smooth muscle cell apoptosis represents a novel therapeutic target for the control of hypertensive vessel remodeling in response to therapeutic agents.

Inhibitory effect of an angiotensin II type 1 receptor antagonist on growth of vascular smooth muscle cells from spontaneously hypertensive rats

To investigate the role of endogenous angiotensin II (Ang II) in the growth of vascular smooth muscle cells (VSMC), we examined the effect of the novel nonpeptide Ang II type 1 (AT1) receptor antagonist CV-11974 on basal and stimulated-growth of VSMC from normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). CV-11974 inhibited basal DNA synthesis by VSMC from SHR, but not from WKY, in the absence of serum. In the presence of 10% calf serum, DNA synthesis was significantly higher in VSMC from SHR than in cells from WKY, and the inhibitory effect of CV-11974 was attenuated. Ang II dose-dependently stimulated DNA synthesis by VSMC from both rat strains, and this effect was abolished by CV-11974. CV-11974 slightly but significantly suppressed proliferation of VSMC from both rat strains. CV-11974 competitively inhibited the specific binding of 125I-labeled Ang II to VSMC from both rat strains. The angiotensin-converting enzyme inhibitor (ACEI) delapril also reduced basal DNA synthesis by VSMC from SHR, but did not affect proliferation of VSMC from either rat strain. These findings suggest that VSMC from SHR may synthesize Ang II which promotes their basal growth in an autocrine/paracrine manner through the AT1 receptor, and that this system may be associated with the exaggerated growth of VSMC from SHR.

Apoptosis in target organs of hypertension

Apoptosis or programmed cell death frequently parallels abnormalities in cell proliferation and differentiation. As hypertrophy/hyperplasia or remodeling occurs in organs affected by hypertension, we evaluated the degree of apoptosis in the heart, kidney, and brain in situ in genetically hypertensive mice and rats as well as in cultured vascular smooth muscle cells. Apoptosis was characterized by morphological features, DNA fragmentation, and laddering as well as by terminal deoxynucleotidyl transferase labeling of the 3' OH ends of both extracted DNA and tissue sections. The present report provides the first evidence of increased apoptosis in whole organs of genetically hypertensive rat and mouse strains: in the heart of spontaneously hypertensive rats (SHR) and in the heart (ventricular cardiomyocytes), kidney (inner cortex and medulla), and brain (cortex, striatum, hippocampus, and thalamus) of spontaneously hypertensive mice, with a higher effect of apoptotic inducers in cultured aortic smooth muscle cells derived from SHR. Both types of known apoptotic processes, oligonucleosomal cleavage and large DNA fragmentation, were observed in vascular smooth muscle cells, but only the former appeared to be increased in SHR. This study underlines the importance of cell death dysregulation in hypertension, reveals a new route for investigation of the pathogenesis of hypertension, and suggests novel targets of therapeutic intervention.

Hypertension, aging, and myocardial synthesis of heat-shock protein 72

We determined the temperature-induced synthesis of the 72-kD heat-shock protein (hsp72) in hearts of normotensive and spontaneously hypertensive rats (SHR) subjected to whole-body hyperthermia (42.0 +/- 0.5 degrees C for 15 minutes). The animals were studied at three different ages: young (2 months), adult (6 months), and old (18 months). The hsp72 was determined by Western blot analysis using a monoclonal antibody. The results were calculated densitometrically as a percentage of a commercial standard. Young SHR responded to hyperthermic stress with increased synthesis of hsp72 compared with age-matched normotensive rats (298.8 +/- 70.0% versus 88.3 +/- 25.5%). This trend was maintained in adult rats (118.1 +/- 31.0% versus 54.8 +/- 21.3%) but not in old rats (65.3 +/- 29.4% versus 43.6 +/- 15.1%). Aging caused a reduction of hsp72 expression in response to hyperthermic stress in both SHR (4.6-fold) and normotensive rats (twofold). These data show that hearts of young and adult SHR respond to heat shock with enhanced synthesis of hsp72. This abnormal response, attenuated by aging, is independent of the presence and degree of hypertension or hypertrophy and is potentially linked to the genetic determination of the disease.

Enalapril reduces the enhanced 1,2-diacylglycerol content and RNA synthesis in spontaneously hypertensive rat hearts before established hypertension

There is evidence that cardiac hypertrophy in spontaneously hypertensive rats (SHR) occurs before the development of hypertension. 1,2-Diacylglycerol, which is thought to be a second messenger activating protein kinase C, is also produced in excess in SHR hearts at 4 weeks of age, before established hypertension. We determined myocardial 1,2-diacylglycerol content in SHR with and without prazosin and enalapril from 3 to 4 weeks of age. Hearts from untreated SHR had greater RNA and DNA synthesis and greater relative weights at 4 weeks of age than those from Wistar-Kyoto (WKY) rats. There was no difference in triglyceride content or phospholipid species between WKY rats and untreated SHR, except for a higher cholesterol content in SHR. Treatment of SHR with enalapril, but not prazosin, lowered not only 1,2-diacylglycerol content but also RNA synthesis to the levels of WKY rats. Moreover, fatty acids involved in 1,2-diacylglycerol were altered by enalapril despite the lack of a difference between WKY rats and untreated SHR. Prazosin did not have any effect on 1,2-diacylglycerol fatty acid composition. Enalapril may decrease cardiac hypertrophy in SHR by lowering myocardial 1,2-diacylglycerol production.

Vascular smooth muscle cell proliferation and its therapeutic modulation in hypertension

The increased growth potential of vascular smooth muscle cells (VSMCs) represents one of the crucial anomalies responsible for the development of essential hypertension, diabetic macroangiopathy, and atherosclerosis. The exaggerated response to growth factors of VSMC from spontaneously hypertensive rats (SHRs) persists in culture when compared with normotensive Wistar-Kyoto control rats, indicating an intrinsic defect in the hypertension-producing mechanism. This greater proliferation is characterized by two intermediate phenotypes: (1) accelerated entry into the S phase of the cell cycle, which results from hyperresponsiveness to epidermal growth factor and platelet-derived growth factor, and (2) abnormal contact inhibition. The enhanced expression of transforming growth factor beta 1 (TGF-beta 1) messenger ribonucleic acid in SHRs precedes this altered contact inhibition, and only VSMCs from SHRs respond to exogenously added TGF-beta 1 at a high cell density, which suggests that abnormal TGF-beta 1 autoregulation may be implicated in the second phenotype. Platelets contain major growth factors for VSMC. Platelet extracts from hypertensive and diabetic patients present augmented growth-promoting activity on VSMCs, which is most evident when both diseases occur simultaneously. Growth-promoting activity may be further influenced by antihypertensive therapy. This growth-promoting activity is increased by hydrochlorothiazide but not by indapamide, atenolol, or captopril in diabetic hypertensive and nondiabetic hypertensive patients. In conclusion, VSMCs in hypertension manifest an intrinsic growth defect that is modulated by extrinsic platelet growth factors and antihypertensive drugs.

Pathogenesis of the essential hypertensions

The pathogenesis of essential hypertension (EH) is reviewed with a special focus on the development phase or the pre-hypertensive period. Three animal models are presented: the spontaneously hypertensive rat, the Dahl's salt-sensitive rat, and the Milan hypertensive rat. Some of the findings in animal models have inspired new fields and technical approaches for studying EH in man. From the original idea of Page, a new mosaic of various etiological parameters serves as a basis for reviewing the multiple facets of EH in man. One must conclude that EH is heterogeneous disease and most likely every single hypertensive patient belongs to a subgroup of the whole population of hypertensives.

Ultrastructural and functional abnormalities of intestinal and renal epithelium in the SHR

Intestinal calcium transport, renal tubular calcium reabsorption, and plasma 1.25 (OH)2 vitamin D3 (calcitriol) levels have all been reported to be diminished in the spontaneously hypertensive rat (SHR) compared with its genetic control the Wistar Kyoto rat (WKY). In the present study, absorptive duodenal and renal tubular epithelia of 12- to 14-week-old male SHR and WKY were examined by electron microscopy to determine whether such disturbances could be related to structural abnormalities. Patchy loss of microvilli in both duodenal and proximal tubular epithelia was observed in the SHR, whereas brush border membrane was entirely normal in the WKY. Irregular spaces were observed between the basal aspects of SHR intestinal epithelial cells and their basement membrane. In addition, the average height of duodenal and renal microvilli was reduced in the SHR. Two specific markers of the brush border membrane, alkaline phosphatase and villin, as well as the cytoplasmic vitamin-D dependent calcium-binding proteins, CaBP9K and CaBP28K were determined. Duodenal alkaline phosphatase activity was reduced in the SHR, compared with the WKY: 0.145 +/- 0.002 vs. 0.186 +/- 0.002 IE/min.microns 3 x 10(3) brush border, mean +/- SEM, N = 10 pairs, P less than 0.001. However, duodenal villin expression was not different from that of the WKY. Duodenal CaBP9K and renal CaBP28K content was diminished in the SHR: 21.0 +/- 0.80 vs. 29.9 +/- 2.19 micrograms/mg protein, N = 6 pairs, P less than 0.01 for duodenum, and 4.47 +/- 0.39 vs. 7.67 +/- 0.54 micrograms/mg protein, N = 6 pairs, P less than 0.001 for kidney. These data showing structural and functional abnormalities of intestinal and kidney cells in the SHR appear to reflect a disorder of transporting epithelia which may be either intrinsic or related to reduced circulating calcitriol.

Genetic, neurohumoral, and hemodynamic influences on spontaneously hypertensive rat heart development in oculo

To distinguish among genetic, neurohumoral, and hemodynamic explanations for structural and functional differences in the hearts of young spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) control rats, embryonic SHR and WKY rat heart tissue was cultured in the anterior eye chamber of adult SHR and WKY rats. In study 1, atria from E-12 WKY rat embryos grafted into anterior eye chambers of either SHR or WKY host rats achieved a larger size than did SHR grafts by 8 weeks in oculo (2.98 +/- 0.75 and 2.55 +/- 0.32 mm2 vs. 1.80 +/- 0.20 and 2.04 +/- 0.44 mm2). Beating rates did not differ between SHR and WKY rat atria implanted into SHR or WKY host rats. In study 2, ventricles from E-13 embryonic SHR and WKY rat hearts grew to similar size and weight when implanted into SHR or WKY host rats (e.g., SHR hearts, 1.81 +/- 0.32 vs. 1.74 +/- 0.33 mm2; WKY rat hearts, 1.75 +/- 0.29 vs. 2.29 +/- 0.32 mm2). Ventricle grafts from SHR embryos into SHR host rats beat more rapidly (165 +/- 19 beats/min) during weekly measurements than either WKY rat ventricles (92 +/- 9 beats/min in SHR hosts and 99 +/- 9 beats/min in WKY host rats) or SHR ventricles grafted into WKY host rats (109 +/- 7 beats/min, p less than 0.001). In study 3, atria from E-13 SHR and WKY rat embryos were grafted into sympathectomized and intact eye chambers of SHR or WKY host rats. Sympathectomy of the eye chamber compromised growth of grafts into WKY host rats (1.54 +/- 0.24 vs. 0.90 +/- 0.14 mm2) but not SHR hosts (1.54 +/- 0.25 vs. 1.73 +/- 0.24 mm2). Grafts into sympathectomized eye chambers of WKY host rats beat more slowly than grafts into eye chambers with sympathetic innervation intact (282 +/- 14 vs. 202 +/- 14 beats/min); sympathectomy did not alter beating rate of grafts in SHR hosts (266 +/- 14 vs. 255 +/- 18 beats/min). These results suggest that the growth and beating rate of SHR atrial grafts may be less sensitive to sympathetic innervation than WKY rat atrial grafts. In these studies, SHR grafts did not grow larger than WKY heart grafts and did not show an increased intrinsic beating rate, suggesting that the cardiac hypertrophy and increased intrinsic beating rate observed in intact SHR are unlikely to result from direct genetic programming.

Selectively enhanced stimulation of DNA synthesis by EGF in vascular smooth muscle cells from young and adult SHR

Aortic vascular smooth muscle cells isolated from spontaneously hypertensive rats (SHR) replicate in vitro nearly twice as fast as cells isolated from several normotensive control strains of rats. Serum-derived peptide growth factors are known to stimulate cells to enter the DNA synthetic phase of the cell cycle and subsequent mitosis. We have examined the effect of several peptide growth factors to stimulate [3H]thymidine incorporation into DNA in smooth muscle cells isolated from adult (24 wk, hypertensive) SHR and age matched normotensive NIH Black Wistar (NBR) control rats. Our results indicate that the response of the SHR cells to epidermal growth factor (EGF) is selectively enhanced compared to the control NBR cells. PDGF also stimulated DNA synthesis but no significant difference between SHR and NBR was observed. Nerve growth factor and endothelial derived growth factor were not mitotic on either cell line. Additionally, we have found that SHR cells, isolated from young early hypertensive weanling animals before a significant elevation in pressure has occurred, divide at the same rate as adult SHR cells normotensive strains. These results are consistent with the view that genetic changes affecting the cellular response to EGF may influence the development of early hypertensive hyperplasia in the SHR which in concert with other factors aggravates the later development of hypertension.

Abnormalities in growth characteristics of aortic smooth muscle cells in spontaneously hypertensive rats

Comparative studies have shown that cultured vascular smooth muscle cells from spontaneously hypertensive rats (SHR) proliferate to a higher cell number, grow to a greater density, and have greater specific growth rate, particularly at a higher saturation density, than those of the normotensive Wistar-Kyoto (WKY) control rats. The growth difference was not due to varying cell survival nor to attachment ability after passage. The degree of DNA synthesis was estimated by [3H]thymidine incorporation into newly synthesized DNA. [3H]thymidine uptake increased with escalating concentrations of calf serum and reached a plateau at 5% calf serum in WKY rats, whereas an excessive, continuous rise was observed in SHR with up to a 20% concentration. [3H]thymidine incorporation into newly synthesized DNA was tested after stimulation by platelet-derived growth factor and epidermal growth factor. A significantly higher amount of newly synthesized DNA in vascular smooth muscle cells from SHR was noted when the cells were stimulated by platelet-derived growth factor or epidermal growth factor alone, and their simultaneous addition did not significantly change the 50% effective concentration but heightened the maximal response. These data provide evidence of increased aortic smooth muscle cell proliferation from aortas of SHR after mitogen stimulation and suggest a defect in growth stimulatory-inhibitory control.

Insulin-like growth factors and neonatal cardiomyocyte development: ventricular gene expression and membrane receptor variations in normotensive and hypertensive rats

Defined factors regulating or influencing mammalian ventricular myocyte (cardiomyocyte) development are not known at this time. During early neonatal ventricular growth, cardiomyocytes begin a 'transition phase' of development toward cellular maturation (hypertrophy) that entails terminal proliferation and cellular binucleation. Insulin-like growth factor-I and -II (IGFs) are believed to play a major role in mammalian postnatal and fetal growth, possibly functioning in local environments which facilitate autocrine or paracrine tissue growth characteristics. Therefore, we examined the expression of the IGF genes and their corresponding membrane receptors in ventricles of normotensive and spontaneously hypertensive (SHR) rat pups during the first 7-14 days of age. We have determined: (1) by receptor crosslinking that neonatal ventricular membranes possess type 1 and type 2 IGF receptors; (2) by receptor binding analysis that type 1 IGF receptor concentration is elevated between days 1-7 in the SHR and shows an age-related decline in concentration and an increase in affinity in both strains; (3) by Northern blot analysis that neonatal rat ventricular tissue expresses primarily IGF-II RNA transcripts of 3.6, 2.3 and 1.7 kilobases (kb) in size, with low levels of IGF-I transcripts detected; (4) by slot-blot hybridization that SHR ventricles contain higher levels of IGF-II transcripts at 3 days of age; and (5) localized the IGF transcripts to ventricular myocytes by tissue in situ hybridization. These observations support a role for cardiomyocyte-produced IGFs that may be locally produced and act in an autocrine or paracrine fashion to modulate cardiomyocyte growth and maturation in the developing rat heart. Because both IGF receptor and IGF RNA transcript parameters differed in SHR hearts, genetically predisposed to hypertrophy, a potentially important biochemical alteration may be associated with the fetal/neonatal growth abnormalities of the developing heart in this rat strain.