Genetic Model Of Hypertension Research Articles

Circadian rhythms in renal function in hypertensive TGR(mRen-2)27 rats and their normotensive controls.

Patients with secondary hypertension frequently display abnormal circadian blood pressure profiles, characterized by a failure to decrease blood pressure at night. The transgenic TGR(mRen-2)27 rat strain, developing fulminant hypertension after the mouse salivary Ren-2 renin gene has been integrated into its genome, provides a fundamental model of genetic hypertension. Because of an inverse circadian blood pressure profile and an unchanged rhythmic pattern of heart rate compared with the normotensive Sprague-Dawley (SPR) strain, it was proposed to serve as an animal model of genetic hypertension. It was the aim of the present study to investigate the circadian rhythmicity in renal function of the transgenic rat to determine whether hypertension and disturbed circadian blood pressure profile would affect kidney function. Urinary water, electrolyte, and protein excretion, as well as glomerular filtration rate and renal plasma flow, were determined in unrestrained freely moving transgenic hypertensive (TGR) and SPR normotensive control rats by collecting urine and arterial blood every 4 h. Significant and similar circadian rhythms were found in renal excretion and hemodynamics in both normotensive and hypertensive strains. Peaks occurred in the active dark period, whereas troughs were found in daytime for all parameters. However, it has to be pointed out that, although the circadian profiles were not grossly perturbed in hypertensive animals, some small differences between SPR and TGR strains did exist in renal function. These discrepancies were precisely related to acrophase, showing a slight phase delay, and also to relative amplitude in TGR. This study demonstrates that the inverted circadian blood pressure profile affected only slightly the circadian rhythms in kidney function in TGR compared with SPR. These findings support the notion that time-dependent changes in systemic blood flow may be of greater importance for circadian regulation of kidney function than systemic blood pressure.

Elevated epidermal growth factor receptor levels in hypertensive Lyon rat kidney and aorta.

1. The adult spontaneously hypertensive Lyon rats (LH strain) exhibited increased maximal epidermal growth factor (EGF) binding in freshly prepared kidney and aortic tissue membranes compared with age-matched normotensive (LN) or hypotensive (LL) strains. However, the binding affinity of the receptors to EGF was the same in all the three strains studied. These findings indicate an increased number of EGF receptors (EGFR) in the hypertensive LH strain. 2. Protein tyrosine kinase activity associated with the EGFR was also elevated in the LH strain compared with LN or LL strains, indicating that these receptors are functionally active. 3. There was a correlation between maximal EGF binding by aortic membranes and blood pressure in individual animals (r = 0.55; P < 0.001). 4. Taken together with previously reported similar findings in other models of genetic hypertension, the present results suggest a possible role for increased levels of EGFR in the development and maintenance of genetic hypertension.

Cell calcium handling and intracellular pH regulation in hereditary hypertriglyceridemic rats: Reduced platelet response to thrombin stimulation

Multiple cell membrane alterations have been described in humans and animals with various genetic forms of hypertension and/or dyslipidemia. The aim of our study was to characterize some properties of platelets and/or erythrocytes (cytosolic calcium handling, intracellular pH regulation and thrombin responsiveness) in a new model of genetic hypertension associated with hyperlipidemia — Prague hereditary hypertriglyceridemic (HTG) rats. There were no differences in basal cytosolic Ca 2+ values in platelets or erythrocytes of HTG rats and control Wistar rats. Ca 2+ influx into erythrocytes was also similar in HTG and control rats. In both strains Ca 2+ influx correlated positively with plasma triglycerides. The slope of this relationship was less steep in HTG than in Wistar rats. Cytosolic Ca 2+ response to thrombin stimulation was smaller in HTG platelets, which were also characterized by a major reduction of thrombin-induced Mn 2+ entry through receptor-operated Ca 2+ channels. Platelets of HTG rats had the same basal intracellular pH i values and similar buffering capacity as control rats but their pH i response to thrombin stimulation was substantially reduced. It can be concluded that reduced responsiveness to thrombin stimulation is a major alteration found in platelets of hypertensive hereditary hypertriglyceridemic rats.

Ca(2+)-dependent mitogen-activated protein kinase activation in spontaneously hypertensive rat vascular smooth muscle defines a hypertensive signal transduction phenotype.

The mechanisms responsible for altered vascular smooth muscle cell (VSMC) function in hypertension remain unknown. In the spontaneously hypertensive rat (SHR) model of genetic hypertension, there are multiple abnormalities in VSMC function, including increased growth, Na(+)-H+ exchange, and increased signal transduction by protein kinase C. The family of kinases termed mitogen-activated protein (MAP) kinases has recently been shown to be essential mediators of growth factor signal transduction. In the present study, alterations in MAP kinase function in the hypertensive phenotype were investigated using early-passage SHR and Wistar-Kyoto (WKY) VSMCs stimulated with angiotensin II (Ang II, 100 nmol/L) or platelet-derived growth factor-BB (PDGF-BB, 10 ng/mL). MAP kinase activity was measured by in-gel kinase assays and Western blot analysis. Two differences between SHR and WKY rats were observed for Ang II-mediated MAP kinase activation: (1) Inactivation after Ang II stimulation was more rapid in SHR than WKY VSMCs. (2) Activity in SHR VSMCs showed a greater dependence on Ca2+ mobilization, since chelation of intracellular Ca2+ with BAPTA inhibited maximal activity by 95% in SHR VSMCs but by only 50% in WKY VSMCs. In contrast to the results with Ang II, no differences in PDGF-stimulated MAP kinase activity were observed. These findings establish activation of MAP kinase by Ang II as a feature that distinguishes SHR VSMCs from WKY VSMCs and suggest that differences in regulation of MAP kinase signaling may alter cellular events that are increased in the SHR genetic model of hypertension.

Na+, K+‐pump activity and skeletal muscle contractile deficits in the spontaneously hypertensive rat

Skeletal muscles in an animal model of genetic hypertension (the spontaneously hypertensive rat. SHR) exhibit significant deficits in contractile performance. These deficits appear to be unrelated to the rise in blood pressure. Slow-twitch soleus muscles show a decrease in specific muscle tension and a reduced resistance to muscle fatigue during prolonged contractile activity. We tested the hypothesis that the reduced fatigue resistance occurs as a consequence of an impaired ability to maintain or restore Na+ and K+ balance across the sarcolemma during repeated contractions. This may result from a genetically based increase in the Na+ permeability of SHR muscles, coupled with a reduction Na+, K+ pump capacity as the animals mature. Soleus muscles in adult SHR exhibit a significant increase in intracellular Na+ content and a significant decrease in intracellular K+ content at rest. B6RB+ uptake in Na(+)-loaded hypertensive muscles is 45% less than predicted from the number of ouabain-binding sites available. Activation of Na+, K+ pumps using adrenaline or insulin produces a significantly smaller hyperpolarization in hypertensive soleus than in control muscles. Control soleus muscles are hyperpolarized for at least 10 min after a 4 min period of high-frequency activity, but hypertensive soleus muscles remain at resting polarity. Nonetheless, the number of ouabain-binding sites in hypertensive muscle is significantly greater than in control soleus, and binding affinities are similar. This apparent deficit in pump capacity might lead to a greater and more prolonged increase in extracellular K+ during repetitive contractions,and an associated decline in tension. Recently, we have been able to prevent the abnormal decrease in hypertensive soleus fatigue resistance by long-term treatment (8 weeks) with the Ca2+ blocker amlodipine. The therapy prevented or reversed the contractile deficits, but did not restore the responsiveness of the Na+, K+ pump to hormonal stimulation. The current data suggest that both a reduction in Na+, K(+)-pump capacity and changes in Ca2+ distribution play a role in the development of contractile deficits in hypertensive muscles.

Renal Sympathetic Neural Mechanisms as Intermediate Phenotype in Spontaneously Hypertensive Rats

The borderline hypertensive rat, the F1 of a cross between a hypertensive spontaneously hypertensive rat (SHR) and a normotensive Wistar-Kyoto (WKY) rat, is a NaCl-sensitive model of genetic hypertension. In addition to hypertension, borderline hypertensive rats fed 8% NaCl develop characteristic alterations in the regulation of efferent renal sympathetic nerve activity and the neural control of renal function that are similar to those observed in the SHR parent. Like the normotensive WKY rat parent, borderline hypertensive rats fed 1% NaCl remain normotensive and do not exhibit these alterations in renal sympathetic neural mechanisms. These renal sympathetic neural mechanisms constitute a complex quantitative trait that may represent an intermediate phenotype. They have a plausible pathogenetic role in hypertension and are different between SHR and WKY rats. This study evaluated two aspects of this complex quantitative trait, enhanced renal sympathoexcitation with air-jet stress and enhanced renal sympathoinhibition with guanabenz, as a candidate intermediate phenotype. As neither of these aspects was observed in two-kidney, one clip Goldblatt-hypertensive rats, this suggests that the trait is not secondary to hypertension from an acquired cause. In a backcross population (F1 x WKY) fed 8% NaCl for 12 weeks, both enhanced renal sympathoexcitation with air-jet stress and enhanced renal sympathoinhibition with guanabenz cosegregated with the hypertension. These results support renal sympathetic neural mechanisms as an intermediate phenotype in SHR.

Recombinant erythropoietin increases blood pressure in experimental hypertension and uraemia without change in vascular cytosolic calcium.

The mechanism of erythropoietin-induced hypertension in dialysis patients is unclear. Intracellular calcium ([Ca2+]i) may be altered in both hypertension and uraemia, and the effects of both uraemia and r-HuEPO on vascular smooth muscle [Ca2+]i and blood pressure (BP) in Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) were therefore studied. Male WKY and SHR underwent partial nephrectomy or sham operation. Three weeks later a 28-day period of treatment with either r-HuEPO 100 U/kg, s.c., 3 times/week or buffer was commenced (n = 10-12 for each subgroup). BP was measured weekly, by noninvasive Doppler tail-cuff assessment. [Ca2+]i was measured following loading with fura-2 in pooled, primary aortic vascular smooth muscle cells (VSMC). Serum urea and creatinine rose 3- to 4-fold after partial nephrectomy. Treatment with r-HuEPO did not change renal function further in either uraemic or control WKY or SHR. Haemoglobin increased in both non-uraemic WKY (16.2-20.3 g/dl) and SHR (16.4-20.5 g/dl) and uraemic animals (WKY 13.9-20.9; SHR 13.8-18.8 g/dl; p < 0.01 for all changes) following 4 weeks of r-HuEPO treatment. BP was unaffected by r-HuEPO in WKY but increased in nonuraemic SHR (210-250; p < 0.01) and in uraemic SHR (224-251 mm Hg; p < 0.001) at 4 weeks. VSMC [Ca2+]i was higher in SHR than WKY (121 vs. 83 nmol/l; MANOVA p < 0.05) but no effect of uraemia or r-HuEPO on [Ca2+]i was detected. In conclusion, the hypertensive effects of r-HuEPO are augmented both in a genetic model of hypertension and in uraemia. Although VSMC [Ca2+]i was elevated in SHR, the further increase in BP induced by r-HuEPO was not associated with alterations in VSMC cytosolic calcium.

Thyrotropin-Releasing Hormone Hyperactivity in the Preoptic Area of Spontaneously Hypertensive Rats

Thyrotropin-releasing hormone (TRH) plays an important role in central cardiovascular regulation through the activation of different neurotransmitter systems at distinct extrahypothalamic sites. To study possible alterations in the TRH system in the hypertensive state, we measured TRH concentration in cerebrospinal fluid and TRH content of the preoptic area in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) by radioimmunoassay. In addition, we also measured the density of the TRH receptor in this area by a rapid filtration technique using [3H]methyl-TRH. We found a significant increase in both the TRH content (634 +/- 61 versus 350 +/- 26 pg/mg protein, SHR versus WKY; P < .01, n = 5) and density of TRH receptors without changes in affinity (Bmax, 5.0 +/- 0.1 versus 3.3 +/- 0.1 fmol/mg protein, P < .01, n = 4). An increase in TRH concentration was also found in the cerebrospinal fluid of SHR (30 +/- 3 versus 21 +/- 2 pg/mL, P < .01, n = 5), suggesting increased TRH release in the central nervous system. Northern blot analysis indicated a threefold augmented abundance of TRH precursor mRNA in the preoptic area of SHR. A polyclonal antibody raised against TRH injected peripherally or intracerebroventricularly lowered arterial blood pressure in SHR but not in WKY. In addition, long-term treatment with enalapril (5 mg/kg twice daily), which was effective in inhibiting serum angiotensin-converting enzyme activity by more than 50%, decreased arterial blood pressure and preoptic area TRH content of SHR, whereas another vasodilator, diltiazem (10 mg/kg every 8 hours), failed to produce a similar change.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of gender on basal nitric oxide release in a model of genetic hypertension

Annual Scientific Meeting of the British Hypertension Society. University of Strathclyde, Glasgow, Scotland 11–13 September 1995: PDF Only

Is the M1-muscarinic receptor a candidate gene for hypertension in the spontaneously hypertensive rat?

1. Central nervous system muscarinic receptors have been implicated in genetic models of hypertension as well as in stress adaptive cardiovascular responses. To determine if the sequence of the M1-muscarinic receptor is pathogenetic for hypertension, we analysed the differences between SHRLJ (spontaneously hypertensive rats) and WKYLJ (Wistar-Kyoto) rats in the sequence of the M1-receptor gene. 2. Specific primer sets were synthesized so as to cover the gene in 10 fragments (158-344 base pairs) with overlaps. Analysis was conducted by both polymerase chain reaction (PCR)-acrylamide and by single-stranded conformation polymorphism (SSCP). 3. No polymorphic locus was found by non-denaturing PCR-acrylamide nor by denaturing SSCP. Slight intrastrain variations in fragment 2 of the parental strains were examined by direct sequencing; however, no difference in sequence was found between SHRLJ and WKYLJ. To identify the chromosomal location and possible linkage with a polymorphic locus, rat/mouse somatic hybrid cell lines were examined. The rat M1-muscarinic receptor was assigned to chromosome 1. 4. Based on analysis of the coding sequence of the gene, our data do not support the hypothesis that the M1-muscarinic receptor is a candidate gene for hypertension. We conclude that, pending analyses of the promoter and regulatory regions of the gene, differences in the M1-muscarinic receptor in SHR either in receptor expression or in physiological response must be due to altered intracellular signalling or extracellular transynaptic events, but not due to a mutation of the gene sequence.

Structural and functional properties of isolated, pressurized, mesenteric resistance arteries from a vasopressin-deficient rat model of genetic hypertension.

In this study we examined the structural and functional properties of mesenteric resistance arteries isolated from normotensive and hypertensive vasopressin-deficient rats. Hypertensive rats had a significantly higher mean arterial pressure (176 +/- 3 mm Hg) than normotensive controls (121 +/- 2 mm Hg). First- and second-order mesenteric resistance arteries were set up in a pressure myograph and pressurized to the mean arterial pressure of the rat from which they had been isolated. Vessels were fixed with glutaraldehyde, embedded in Araldite, sectioned, and examined histologically. First- and second-order mesenteric resistance arteries from hypertensive rats displayed a reduced internal diameter and increased media-to-lumen ratio compared with their normotensive controls. However, there was no evidence for an increased media content, indicating that the reduced internal diameter of hypertensive arteries was consequent to either remodeling of similar amounts of wall material or a reduced artery distensibility but not vascular growth. Pressurized arteries were also examined with respect to their responsiveness to the vasoconstrictors norepinephrine and arginine vasopressin and to the endothelium-dependent vasodilator acetylcholine and the endothelium-independent vasodilator papaverine. Both first- and second-order mesenteric arteries from hypertensive rats displayed enhanced sensitivity to norepinephrine compared with their normotensive controls. This effect was specific for norepinephrine, because responses to arginine vasopressin were similar in vessels isolated from normotensive and hypertensive rats. No evidence was found for an impaired endothelium-dependent vasodilatation in arteries from hypertensive rats. Indeed, in hypertensive vasopressin-deficient rats responses to acetylcholine were increased in first-order arteries compared with those from normotensive rats. Responses to papaverine were similar in arteries isolated from either normotensive or hypertensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Defective ANF-R2/ANP-C receptor-mediated signalling in hypertension.

In the present studies we have shown that atrial natriuretic factor (peptide) receptor of ANF-R2/ANP-C type is coupled to adenylyl cyclase/cAMP signal transduction system through Gi-regulatory protein and is implicated in mediating some of the physiological responses of atrial natriuretic factor or peptide (ANP). ANF-R2/ANP-C receptor-mediated adenylyl cyclase inhibition was altered in hypertension. This alteration was tissue specific. In heart, aorta, brain and adrenal, the extent of inhibition of adenylyl cyclase by ANP was enhanced in SHR as compared to age-matched WKY, whereas in platelets, the ANP-mediated inhibition was completely attenuated. The enhanced inhibition of adenylyl cyclase by ANP was also observed in heart and aorta from DOCA-salt hypertensive rats. In addition, the augmented inhibition of adenylyl cyclase by ANP was observed in 2 weeks and older SHR but not in 3-5 days old SHR. Similarly, in DOCA-salt hypertensive rats, the enhanced inhibition of adenylyl cyclase by ANP was observed after 2 weeks of DOCA-salt treatment when the blood pressure was also enhanced, however one week older SHR but not in 3-5 days old SHR. Similarly, in DOCA-salt hypertensive rats, the enhanced inhibition of adenylyl cyclase by ANP was observed after 2 weeks of DOCA-salt treatment when the blood pressure and augmented ANP-mediated inhibition of adenylyl of DOCA-salt treatment did not result in an augmented blood pressure and augmented ANP-mediated inhibition of adenylyl cyclase, suggesting that blood pressure increase may be responsible for the enhanced responsiveness of ANP to adenylyl cyclase inhibition. However, in genetic model of hypertension, the increased inhibition of adenylyl cyclase by ANP at 2 weeks of age (when the blood pressure is normal) may be implicated in the pathogenesis of hypertension. The augmented inhibition of adenylyl cyclase in cardiovascular tissues from SHR and DOCA-salt hypertensive rats may be due to the upregulation of ANF-R2/ANP-C receptors or due to the amplification of post-receptor signalling mechanisms.

α 1-Adrenergic receptors in cardiac ventricles of dahl rats

This study was designed to examine the effects of sex, age, and a high-salt diet on cardiac alpha 1-adrenoceptors in an animal model of genetic hypertension, the Dahl salt-sensitive rat. Ventricular alpha 1-adrenoceptors were measured by radioligand binding with [3H]prazosin in membrane fractions in Dahl S and R rats of 7, 12, and 15 weeks of age. In both S and R rats, the maximal binding (Bmax) of alpha 1-adrenoceptor binding was greater in male than in female rats. The Bmax decreased with age in both the S and R strains; at 12 weeks of age, Bmax was approximately one-half of that observed at 7 weeks of age in both S and R strains. In the rats fed a high-salt diet, the Bmax tended to be greater in S rats than in R rats at 12 weeks of age and this difference became significant at 15 weeks of age. A significant positive correlation was found between the Bmax and the heart-to-body weight ratio in the Dahl S and R rats. The dissociation constant (Kd) was not different between male S and R rats at each age. These results suggest that the ventricular alpha 1-adrenoceptor may be involved in cardiac hypertrophy in Dahl rats.

Expression of endothelin-1 gene in blood vessels of adult spontaneously hypertensive rats

Endothelins are potent vasoconstrictor peptides produced by the endothelium of blood vessels and other tissues, which could play a potentially important pathogenic role in hypertension. In some hypertensive models, endothelin production in blood vessels is enhanced. We have therefore investigated endothelin-1 gene expression in arteries of 17-week old spontaneously hypertensive rats (SHR) with established hypertension and Wistar-Kyoto control rats (WKY). The abundance of endothelin-1 mRNA in aorta and mesenteric arteries was evaluated by Northern blot analysis. Endothelin-1 mRNA expression was found to be reduced in the aorta of SHR in comparison to the age-matched WKY, whereas it was similar in mesenteric arteries in both strains. These results agree with the vascular content of immunoreactive endothelin-1 which we previously reported, and indicate that reduced or normal vascular endothelin-1 content in SHR is not the result of rapid turnover of the peptide in SHR blood vessels. Together with normal plasma immunoreactive endothelin-1 and normal or reduced responsiveness of blood vessels of SHR to endothelin-1, this indicates that vascular endothelin-1 does not appear to play an important role in the pathogenesis of the elevation of blood pressure in this model of genetic hypertension.

Neuropeptide Y

To evaluate whether neuropeptide Y (NPY) is likely to be relevant as a regulator of cardiovascular function in general and of blood pressure control in arterial hypertension in particular, based on a literature survey. NPY is a putative cotransmitter of many central and peripheral sympathetic neurons. It and its receptors are present in brain areas and peripheral tissues involved in cardiovascular regulation, and administration of exogenous NPY to these sites can elicit functional cardiovascular responses by acting on specific pre- and postsynaptic receptors. Moreover, NPY may act as a growth factor for the development of vascular and cardiac hypertrophy. The release of NPY and postsynaptic vasoconstriction responses to NPY may be enhanced in hypertension, whereas presynaptic inhibitory responses may be attenuated. Some of these alterations may precede the development of blood pressure elevations in the spontaneously hypertensive rat model of genetic hypertension. NPY might be an important physiological and pathophysiological modulator of cardiovascular function, but further studies using specific high-affinity antagonists are required.

Overflow of endogenous norepinephrine from PVH nucleus of DOCA-salt hypertensive rats.

Previous studies from this laboratory demonstrated that there was enhanced basal and evoked (K+ depolarization) overflow of endogenous norepinephrine (NE) into the perfusate of a push-pull cannula placed in the paraventricular nucleus of the hypothalamus (PVH) of conscious freely moving spontaneously hypertensive rat (SHR) compared with Wistar-Kyoto (WKY) or Sprague-Dawley (SD) rats. The present study was carried out to determine whether results obtained with SHR were specific to this genetic model of hypertension by examining NE release in deoxycorticosterone acetate (DOCA)-salt hypertension. DOCA-salt hypertension was produced in 8-wk-old uninephrectomized SD rats by administering a 50-mg DOCA Silastic pellet subcutaneously 7 days postnephrectomy and providing 0.9% NaCl + 0.2% KCl drinking solution at libitum for 3 wk. Sham-implanted animals received normal tap water. Blood pressure was similar to that of 8- to 10-wk-old SHR. Basal release of NE as well as release after K+ added to the push-pull cannula or sodium nitroprusside or phenylphrine administered intravenously was determined. It was observed that there was no difference in basal overflow or after K+ administration in DOCA-salt hypertensive rats compared with sham animals. Similarly, the increase in NE overflow due to sodium nitroprusside or the decrease due to phenylphrine was similar between DOCA-salt rats or sham controls. This was in sharp contrast to what was observed in SHR: basal or K(+)-evoked release was significantly greater in SHR than WKY, SD, DOCA-salt, or DOCA-sham controls. It is concluded that central noradrenergic activity involving the PVH is not altered in DOCA-salt hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

933-93 The Regression of Left Ventricular Myofibrillary Proteins by ACE-inhibition (Lisinopril) is Associated with an Increase in Protein Synthetic Rates in Vivo

One of the most serious complications of systemic hypertension is myocardial tissue damage, including left ventricular hypertrophy, as a consequence of increased protein synthesis. However, the modulating role of translational events in the hypertrophy-regression transition is poorly understood, especially where therapeutic regimes have been employed. These events were investigated in vivo in a genetic model of hypertension, namely in the spontaneously hypertensive rat (SHR); comparative responses were investigated in normotensive Wistar Kyoto rats (WKY). Rats were used at 4 months of age and treated with either the ACE-inhibitor lisinopril (5 mg/kg/day) in tap water or plain tap water (controls). The groups were assigned as follows: WKY-CON, normotensive controls; WKY-LIS, normotensives plus lisinopril; SHR-CON, hypertensive controls; SHR-LIS, hypertensives plus lisinopril. Fractional rates of protein synthesis (k s defined as the percentage of the myofibrillary protein pool renewed each day; %/day) were measured in vivo with the flooding dose technique using L-[4 -3 H]phenylalanine. Left ventricular myofibrillary proteins were extracted by differential solubility and high-speed centrifugation techniques; purity was assessed with SDS-PAGE. After 8 weeks treatment the myofibrillary protein contents (mg per region) in normotensive rats were as follows (all data as mean ± SEMS, n = 6–9): WKY-CON, 45 ± 1 mg; WKY–LIS, 36 ± 1 (p &lt; 0.001). In the hypertensive group regression of contractile protein content occurred; i.e., SHR-CON, 52 ± 3 mg; SHR-L1S, 38 ± 1 mg (p &lt; 0.001). Corresponding k s values were: WKY-CON, 8.3 ± 0.2 %/d; WKY–LIS, 8.2 ± 0.3 %/d (NS). In the SHR-group k s values were: SHR-CON, 8.2 ± 0.3%/d; SHR-L1S, 9.2 ± 0.3 mg (p &lt; 0.025) ACE-induced regression of contractile protein composition in hypertension is associated with an increase in rates of translation

Abnormal regulation of cytosolic free calcium in vascular endothelial cells from spontaneously hypertensive rats

To investigate whether the resting cytosolic free calcium concentration and the agonist-induced increase in this concentration in vascular endothelial cells from spontaneously hypertensive rats (SHR) differ from those in normotensive Wistar-Kyoto (WKY) rats. The Fura-2 fluorescence technique was used to monitor changes in cytosolic free calcium concentration in isolated aortic endothelial cells from SHR (aged 12 weeks) and age-matched WKY rats. Aortic endothelial cells from primary culture to the third passage were used. The cells were grown to a confluent monolayer on coverslips before the fluorescent measurement of cytosolic free calcium concentration. The resting cytosolic free calcium concentration and changes in it induced by bradykinin, endothelin 1, angiotensin II and thapsigargin were examined and compared between endothelial cells from SHR and WKY rats. The resting cytosolic free calcium concentration in aortic endothelial cells was significantly lower in SHR than in WKY rats. Bradykinin induced a lesser increase in cytosolic free calcium concentration in endothelial cells from SHR than in those from WKY rats. However, aortic endothelial cells both from SHR and from WKY rats had a similar calcium response to endothelin 1 and angiotensin II. Furthermore, the thapsigargin-induced increase in cytosolic free calcium concentration was significantly less in SHR than in WKY rat endothelial cells. These results suggest that the altered calcium response to bradykinin in endothelial cells from SHR could be caused by an alteration of bradykinin receptors or changed bradykinin degradation. Alternatively, the intracellular calcium stores that are sensitive to thapsigargin and bradykinin may differ from those that are activated by endothelin 1 and angiotensin II in SHR aortic endothelial cells. A lower level of resting cytosolic free calcium concentration and the impaired bradykinin-induced increases in it in SHR endothelial cells could reflect dysfunction of vascular endothelium underlying a reduced endothelium-dependent vasorelaxation in this genetic hypertension model.

Central effects of irbesartan, an AT 1 antagonist in rats

We evaluated if chronic blockade of bradykinin B2-receptors by the long-acting antagonist Icatibant (D-Arg,‘Hyp3,Thi5,D-Tic7,Oic8’-bradykinin) affects blood pressure of rats. Pairs of normotensive Wistar Kyoto rats or spontaneously hypertensive rats were mated and their offspring received Icatibant (25 nmol day−1per kg body wt., s.c.) or vehicle from the 2nd day until the 7th week of life. Then, the administration of Icatibant or vehicle was continued by i.p. infusion using Alzet osmotic pumps. At 9 weeks of age, normotensive rats given Icatibant showed greater systolic blood pressure (135±1vs115±1 mmHg in vehicle-treated rats,P<0.01), while heart rate was similar. The group difference regarding blood pressure levels was confirmed by direct intra-arterial measurement. No difference was detected between vehicle- and Icatibant-treated spontaneously hypertensive rats regarding blood pressure increase with aging. In conclusion, chronic blockade of bradykinin receptors by Icatibant alters the adult cardiovascular phenotype of Wistar Kyoto rats, provided that the antagonist is given at the early phases of life. These results suggest that the B2-receptor is essential for the maintenance of cardiovascular homeostasis during development, whereas it does not exert a protective role against the progression of hypertension in a rat model of genetic hypertension.

Kinetics of Na+/H+ exchange in vascular smooth muscle cells from WKY and SHR: effects of phorbol ester.

The kinetic properties of Na+/H+ exchange were investigated in vascular smooth muscle cells (VSMC) in culture from normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Antiport activity was measured in 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein-loaded cells after nigericin-induced cytosolic acidification. Studies were performed without (control) and with pretreatment of the cells with phorbol 12-myristate 13-acetate (PMA; 200 nM). Na+/H+ exchange markedly differed between the two strains with lower Hill coefficients [1.56 +/- 0.17 (SE) vs. 2.62 +/- 0.36] and higher maximal activity (Vmax) values (55.85 +/- 5.24 vs. 31.11 +/- 2.38 mmol H+.l-1.min-1) in SHR compared with WKY cell lines. PMA markedly altered the antiport kinetics in WKY VSMC with a decrease in the Hill coefficient (1.75 +/- 0.14) without affecting Vmax (31.88 +/- 1.55 mmol H+.l-1.min-1). In VSMC from SHR, PMA had no effect on the kinetic variables investigated. Thus two kinetic abnormalities are present with respect to Na+/H+ antiport activity in VSMC from SHR compared with WKY, i.e., increased Vmax and decreased Hill coefficient. The observation that PMA does not affect the kinetics of the Na+/H+ antiport in VSMC from SHR suggests a marked degree of antiporter prestimulation in this animal model of genetic hypertension.