Induction of FOS expression by acute immobilization stress is reduced in locus coeruleus and medial amygdala of Wistar–Kyoto rats compared to Sprague–Dawley rats

Activation of the brain noradrenergic system during acute stress is thought to play an important integrative function in coping and stress adaptation by facilitating transmission in many brain regions involved in regulating behavioral and physiologic components of the stress response. Compared with outbred control Sprague-Dawley (SD) rats, inbred Wistar-Kyoto (WKY) rats exhibit an exaggerated hypothalamic-pituitary-adrenal (HPA) response as well as increased susceptibility to certain forms of stress-related pathology. However, we have also shown previously that WKY rats exhibit reduced anxiety-like behavioral reactivity to acute stress, associated with reduced activation of the brain noradrenergic system. Thus, to understand better the possible neurobiological mechanisms underlying dysregulation of the stress response in WKY rats, we investigated potential strain differences in stress-induced neuronal activation in brain regions that are both involved in regulating behavioral and neuroendocrine stress responses, and are related to the noradrenergic system, either as targets of noradrenergic modulation or as sources of afferent innervation of noradrenergic neurons. This was accomplished by visualizing stress-induced expression of Fos immunoreactivity in the paraventricular nucleus of the hypothalamus, lateral bed nucleus of the stria terminalis, central nucleus of the amygdala, and medial nucleus of the amygdala (MeA), as well as the noradrenergic nucleus locus coeruleus (LC). Stress-induced Fos expression was found to be decreased in the LC and MeA of WKY rats compared with similarly stressed SD rats, whereas no strain differences were observed in any of the other brain regions. This suggests that strain-related differences in activation of the MeA may be involved in the abnormal neuroendocrine and behavioral stress responses exhibited by WKY rats. Moreover, as the MeA is both an afferent as well as an efferent target of the brainstem noradrenergic system, reduced MeA activation may either be a source of reduced noradrenergic reactivity seen in WKY rats, or possibly a consequence. Nonetheless, understanding the mechanisms underlying altered stress reactivity in models such as the WKY rat may contribute to a better understanding of stress-related psychopathologies such as depression, post-traumatic stress disorder or other anxiety disorders.

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

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

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

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

Renin antisense injected intraventricularly decreases blood pressure in spontaneously hypertensive rats

Brain renin-angiotensin system plays an important role in blood pressure regulation and is suggested to play a role in the development and maintenance of hypertension. To test the hypothesis that brain renin may play a significant role in hypertension in spontaneously hypertensive rats (SHR), phosphorothioated antisense oligodeoxynucleotides targeted to renin mRNA were administered intracerebroventricularly in SHR. Administration of an antisense but not its sense oligodeoxynucleotide produced a prolonged duration of decrease in blood pressure. Intra-arterial administration of the antisense oligodeoxynucleotide at the same dose that decreased blood pressure when administered intraventricularly did not affect blood pressure. Furthermore, renin mRNA but not angiotensin AT1 receptor mRNA levels were decreased in the hypothalamus of the antisense oligodeoxynucleotide-treated rats. These results suggest that brain renin may play a significant role in hypertension in SHR.

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

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

White matter lesions and alteration of vascular cell composition in the brain of spontaneously hypertensive rats

There have been few studies on the white matter lesions of spontaneously hypertensive rats (SHR). From the point of view of hypertension and arteriosclerosis, white matter lesions were examined in SHR and stroke-prone SHR (SHRSP), and were then compared with Wistar-Kyoto (WKY) rats. The vasculopathy was analyzed by morphometric immunohistochemistry for collagen and smooth muscle actin. Both SHR and SHRSP had hypertension at > or = 12 weeks of age, and the latter developed severe white matter lesions at 20 weeks. Immuno- histochemistry revealed proliferation of microglia in the white matter and an increase in smooth muscle actin in the vessels of SHRSP compared with the WKY rats and SHR, but there were no changes in the collagen. These results indicate a role of hypertension in the pathogenesis of white matter lesions. However, genetic difference may also be responsible since SHR and SHRSP showed similar hypertension.

Paradoxical hormonal and behavioral responses to hypothyroid and hyperthyroid states in the Wistar-Kyoto rat

Wistar-Kyoto (WKY) rats show endogenous depressive behavior that can be reversed by antidepressants. Given that WKYs exhibit decreased sensitivity to some antidepressants and treatment-resistant depressed patients often show hypothalamic-pituitary-thyroid (HPT) dysregulation, we examined the behavioral and HPT hormonal responses of WKYs to altered thyroid status. "Euthyroid" WKYs had elevated basal plasma TSH and T(3) levels as compared to Wistars. Hypothyroidism increased TSH levels more in WKYs than in Wistars and increased response latency in the open field test (OFT) of WKYs only. Administration of T(4) and T(3) suppressed plasma TSH equally in both strains. Wistars responded to increased T(3) levels with decreased response latency and increased activity in the OFT, but increased immobility in the forced swim test. In contrast, WKYs responded only to the high T(3) levels with decreased response latency in the OFT. These results suggest the existence of a decreased central nervous system sensitivity to thyroid hormones in WKYs that could be related to their depressive behavior.

Effect of long-term ethanol feeding on brainstem alpha(2)-receptor binding in Wistar-Kyoto and spontaneously hypertensive rats

Our previous studies have shown that ethanol attenuates baroreflex function in Wistar-Kyoto (WKY) but not in spontaneously hypertensive rats (SHRs). The present study determined the effects of chronic ethanol administration on alpha(2)-binding sites in brainstem areas that modulate baroreflexes. In vitro autoradiography was utilized to evaluate the effect of a 3-month ethanol feeding on the density (B(max)) and affinity (K(D)) of alpha(2)-adrenoceptors in the middle (mNTS) and rostral (rNTS) portions of the nucleus tractus solitarius of SHRs and WKY rats. Autoradiographic examination of brainstem sections preincubated with [125I]p-iodoclonidine revealed no inter-strain differences in alpha(2)-binding in control rats. Ethanol feeding caused strain-dependent changes in alpha(2)-binding activity, which comprised significant (P<0.05) decreases in the density of alpha(2)-binding sites in both areas of the NTS in SHRs versus no effect in WKY rats. These findings do not favor a role for brainstem alpha(2)-adrenoceptors in ethanol-induced attenuation of baroreflexes. Interestingly, the ethanol-evoked reduction in the NTS alpha(2)-receptor density in SHRs may explain reported findings that ethanol abolishes the hypotensive effect of the alpha(2)-adrenoceptor agonist clonidine in this rat model.

Deficits in spatial learning and nicotinic-acetylcholine receptors in older, spontaneously hypertensive rats

Spontaneously hypertensive rats are often used as models of attention deficit hyperactivity disorder and to investigate the effects of hypertension on cognitive function. Along with the wide variety of cardiovascular anomalies, these animals as young adults also exhibit deficits in memory and attention and central nicotinic-acetylcholine receptor sites. These findings may have particular significance since nicotinic receptors appear to be involved in the regulation of cerebral circulation and mnemonic function. Furthermore, a lack of high affinity nicotinic receptors (in knockout mice) has also been shown to accelerate both the structural and cognitive degeneration associated with age, findings that may be especially relevant to age-related memory disorders such as Alzheimer's Disease where large deficits in nicotinic receptors are observed. Since spontaneously hypertensive rats appear to be both memory-impaired and deficient in nicotinic receptors at a young age (compared to the non-hypertensive phenotype, Wistar-Kyoto rats), we were interested to learn if these conditions were exacerbated in older animals with particular interest in specific nicotinic receptor subtypes in memory areas of the brain. Spatial learning was assessed in 15-month-old subjects of each phenotype (i.e. hypertensive and non-hypertensive) using a two-phase water maze paradigm, and nicotinic receptors were measured via autoradiography with [125I]-alpha-bungarotoxin and [3H]-epibatidine. In the water maze, both groups learned to locate a hidden platform as indicated by progressively shorter latencies across training days, however, Wistar-Kyoto rats were more efficient in both phases. While the number of both bungarotoxin and epibatidine binding sites was lower in the hypertensive rats across several brain regions, in the case of epibatidine binding, the magnitude of the difference and the number of areas affected was generally greater and included areas important for spatial learning (e.g. frontal and entorhinal cortex). In a direct comparison between 3-month-old and 15-month-old rats of each phenotype, epibatidine sites were markedly reduced by age (i.e. by greater than 50% in some cases) across multiple brain regions in both groups, although Wistar-Kyoto rats appeared to be more substantially affected by age. These data further support the use of the spontaneously hypertensive rat as model for studying learning-impairment and reduced central nicotinic receptors and also indicate that these characteristics persist and (in the case of high affinity nicotinic receptor cites) worsen with age.

Gender-related distinctions in protein kinase C activity in rat vascular smooth muscle

Gender differences in vascular reactivity have been suggested; however, the cellular mechanisms involved are unclear. We tested the hypothesis that the gender differences in vascular reactivity reflect gender-related, possibly estrogen-mediated, distinctions in the expression and activity of specific protein kinase C (PKC) isoforms in vascular smooth muscle. Aortic strips were isolated from intact and gonadectomized male and female Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). Isometric contraction was measured in endothelium-denuded aortic strips. PKC activity was measured in the cytosolic and particulate fractions, and the amount of PKC was measured using Western blots and isoform-specific anti-PKC antibodies. In intact male WKY rats, phenylephrine (Phe, 10(-5) M) and phorbol 12,13-dibutyrate (PDBu, 10(-6) M) stimulated contraction to 0.37 +/- 0.02 and 0.42 +/- 0.02 g/mg tissue wt, respectively. The basal particulate/cytosolic PKC activity ratio was 0.86 +/- 0.06, and Western blots revealed alpha-, delta-, and zeta-PKC isoforms. Phe and PDBu increased PKC activity and caused significant translocation of alpha- and delta-PKC from the cytosolic to particulate fraction. In intact female WKY rats, basal PKC activity, the amount of alpha-, delta-, and zeta-PKC, the Phe- and PDBu-induced contraction, and PKC activity and translocation of alpha- and delta-PKC were significantly reduced compared with intact male WKY rats. The basal PKC activity, the amount of alpha-, delta-, and zeta-PKC, the Phe and PDBu contraction, and PKC activity and alpha- and delta-PKC translocation were greater in SHR than WKY rats. The reduction in Phe and PDBu contraction and PKC activity in intact females compared with intact males was greater in SHR ( approximately 30%) than WKY rats ( approximately 20%). Phe and PDBu contraction and PKC activity were not significantly different between castrated males and intact males but were greater in ovariectomized (OVX) females than intact females. Treatment of OVX females or castrated males with 17 beta-estradiol, but not 17 alpha-estradiol, subcutaneous implants caused significant reduction in Phe and PDBu contraction and PKC activity that was greater in SHR than WKY rats. Phe and PDBu contraction and PKC activity in OVX females or castrated males treated with 17 beta-estradiol plus the estrogen receptor antagonist ICI-182,780 were not significantly different from untreated OVX females or castrated males. Thus a gender-related reduction in vascular smooth muscle contraction in female WKY rats with intact gonads compared with males is associated with reduction in the expression and activity of vascular alpha-, delta-, and zeta-PKC. The gender differences in vascular smooth muscle contraction and PKC activity are augmented in the SHR and are possibly mediated by estrogen.

Reduced production of lactate during hypoxia and reoxygenation in astrocytes isolated from stroke-prone spontaneously hypertensive rats

Lactate production and expressions of monocarboxylate transporter 1 (MCT1) and lactate dehydrogenase (LDH) mRNA after hypoxia and reoxygenation (H/R) were examined by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) using astrocytes in culture isolated from stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar Kyoto rats (WKY). The basal production of lactate in SHRSP was the same as that observed in WKY. In contrast the lactate levels in SHRSP at 1 and 6 h of reoxygenation after hypoxia were significantly lower than those observed in WKY. In addition LDH and MCT1 mRNA expressions in SHRSP were significantly less strong compared with those in WKY during H/R. These findings indicate that decreased production and slow transport of lactate in SHRSP astrocytes are involved in neuronal energy depletion and possibly encourage neuronal damage, although hereditary weakness of cortical neurons is also related to cell death during H/R.

Ca2+ buffering function of sarcoplasmic reticulum in rat tail arteries: comparison in normotensive and spontaneously hypertensive rats

The superficial buffer barrier function of the sarcoplasmic reticulum (SR) during rest and that during stimulation with Bay k 8644, an agonist of L-type Ca2+ channels, were compared in endothelium-denuded strips of tail arteries from 13-week-old normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR), by measuring the effects of cyclopiazonic acid (CPA) and thapsigargin that inhibit SR Ca2+-ATPase and the effect of ryanodine that depletes SR Ca2+. The addition of 10 microM CPA induced a transient contraction that was not significantly different between WKY and SHR. The CPA-induced contraction was strongly inhibited by 100 nM nifedipine and was abolished by Ca2+-free solution in both strains. Thapsigargin (100 nM) or ryanodine (10 microM) induced similar, small transient contractions in the two strains. The addition of Bay k 8644 (1-100 nM) almost failed to induce a contraction in both WKY and SHR. When the strips were preincubated with 10 microM CPA, 100 nM thapsigargin or 10 microM ryanodine, Bay k 8644 induced similar concentration-dependent contractions in the two strains. The amount of Ca2+ stored in the SR, as estimated from the 20 mM caffeine-induced contraction, was not significantly different between WKY and SHR. Our results suggest that the SR of rat tail arteries can buffer a large amount of Ca2+ that enters the cell during the rest and the Bay k 8644 stimulation, and these functions are not altered in SHR.

Clonidine action in spontaneously hypertensive rats (SHR) depends on the GABAergic system function

The effect of gamma-aminobutyric acid (GABA)A antagonists (bicuculline, picrotoxin) on clonidine hypotension in spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats were examined. The GABA turnover changes after clonidine injection in both strains were also studied. Administration of clonidine alone induced the stronger decrease of systolic blood pressure (SBP) in SHR. Co-dosage of clonidine with these agents reduced its hypotensive effect in dose dependent manner and the effectiveness of both antagonists was higher in SHR. We find that clonidine stimulates GABA synthesis in the hypothalamus and the pons-medulla in both strains but the GABA turnover rate is significantly slower in SHR. Therefore, the differences in inhibitory action of GABAA receptor antagonists between WKY and SHR rats may be explained by central GABAergic system dysfunction in the hypertension. Our results indicate that the down regulation of the GABAergic system observed in hypertension may be compensated by the action of clonidine.

Brain dopamine D2 receptor mRNA levels are elevated in young spontaneously hypertensive rats

Levels of brain dopamine D2 receptor expression were compared between spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) controls by quantitative in situ hybridisation, using a complementary RNA probe for D2 receptor mRNA. In SHR which were 6 weeks of age, significantly higher levels of D2 receptor mRNA were found in the caudate-putamen (42%), nucleus accumbens (23%), olfactory tubercle (17%) and substantia nigra (38%) compared to age-matched WKY controls. D2 receptor mRNA levels were also higher in the substantia nigra (27%) of 12-14-week old SHR compared to WKY. The increased levels of dopamine D2 receptor gene expression displayed in young prehypertensive SHR could implicate altered central dopaminergic activity in the pathogenesis of hypertension.

Nitric oxide synthase in the JGA of the SHR: expression and role in tubuloglomerular feedback

The spontaneously hypertensive rat (SHR) has an enhanced tubuloglomerular feedback (TGF) and a diminished buffering by juxtaglomerular apparatus (JGA)-derived NO. We examined the hypothesis that these effects are due to decreases in nitric oxide synthase (NOS) expression or limited availability of L-arginine or tetrahydrobiopterin (BH(4)). SHR had significantly (P < 0.05) greater mRNA abundance (by RT-PCR) or protein (by Western analysis) for neuronal NOS (nNOS, or type I) and endothelial cell NOS (ecNOS, or type III) in renal cortex or isolated glomeruli, respectively. There was prominent expression of ecNOS in glomerular endothelium and nNOS in macula densa. Maximal TGF responses, assessed from changes in proximal stop-flow pressure during orthograde loop of Henle (LH) perfusion, were greater in SHR [Wistar-Kyoto (WKY), 8.1 +/- 0.3 (n = 46) vs. SHR, 10.3 +/- 0.3 mmHg (n = 57); P < 0.001]. Unlike WKY, TGF responses of SHR were unresponsive to microperfusion of the nNOS inhibitor, 7-nitroindazole (7-NI, 10(-4) M) [WKY, 9.5 +/- 0.5 to 13.2 +/- 0.7 (n = 13, P < 0.001) vs. SHR, 11.8 +/- 0.7 to 12.5 +/- 0.6 mmHg (n = 19, not significant)], or to L-arginine (10(-3) M) [WKY, 7.7 +/- 0.8 to 6.3 +/- 0.4 (n = 10, P < 0.05) vs. SHR, 10.4 +/- 0.7 to 10.6 +/- 0.7 mmHg (n = 10, not significant)]. Neither BH(4) (10(-4) M) nor sepiapterin (10(-4) M), its stable precursor, modified TGF responses in WKY or in SHR, nor did they restore a response to microperfusion of 7-NI in SHR. In conclusion, there is a diminished role for NO from nNOS in blunting of TGF in SHR which cannot be ascribed to limited NOS expression or availability of substrate or BH(4).

Comparison of calcium import as a function of contraction in the aortic smooth muscle of Sprague-Dawley, Wistar Kyoto and spontaneously hypertensive rats

Genetic variations of far-reaching consequences have been established between spontaneously hypertensive rats (SHR) and their controls, Wistar Kyoto rats (WKY). The SHR strain is the most widely used model for the study of genetic hypertension. Calcium homeostasis in the vascular smooth muscle (VSM) is controlled by calcium channels and calcium pumps located in both VSM and the overlying endothelial cells that line the large blood vessels and the heart. Hypertension adversely affects calcium homeostasis. Investigations on the import of calcium from extracellular spaces with alpha1-adrenergic stimulation as a function of contractility of VSM cells in SHR and WKY were made and compared with the contractility observed in VSM cells of Sprague-Dawley (CD) rats. Experiments were performed on rings from thoracic aortas of three strains with endothelial lining intact or removed to discern the paracrine control of endothelium on contractility in response to calcium import. The internal stores of Ca2+ were depleted by repeated alpha 1-adrenergic stimulation with phenylephrine (PE) and refilling of these stores was prevented by cyclopiazonic acid (CPA) and/or thapsigargin (TG), two known inhibitors of Ca2+ATPase, the enzyme that drives sarcoplasmic calcium pumps. The two components of tonic muscular contraction, T I and T II, which are known to be due to the flow of Ca2+ from the extracellular gradient controlled via the poly-phosphoinositide cascade and nifedipine sensitive Ca2+ channels were found to be variable among these strains. Implications of these variations are discussed in this report

Fiber type populations and Ca2+-activation properties of single fibers in soleus muscles from SHR and WKY rats

Electrophoretic analyses of muscle proteins in whole muscle homogenates and single muscle fiber segments were used to examine myosin heavy chain (MHC) and myosin light chain 2 (MLC2) isoform composition and fiber type populations in soleus muscles from spontaneously hypertensive rats (SHRs) and their age-matched normotensive controls [Wistar-Kyoto (WKY) rats], at three stages in the development of high blood pressure (4 wk, 16 wk, and 24 wk of age). Demembranated (chemically skinned with 2% Triton X-100), single fiber preparations were used to determine the maximum Ca2+-activated force per cross-sectional area, calcium sensitivity, and degree of cooperativity of the contractile apparatus and Ca2+-regulatory system with respect to Ca2+. The results show that, at all ages examined, 1) SHR soleus contained a lower proportion of MHCI and MLC2 slow (MLC2s) and a higher proportion of MHCIIa, MHCIId/x, and MLC2 fast (MLC2f ) isoforms than the age-matched controls; 2) random dissection of single fibers from SHR and WKY soleus produced four populations of fibers: type I (expressing MHCI), type IIA (expressing MHCIIa), hybrid type I+IIA (coexpressing MHCI and MHCIIa), and hybrid type IIA+IID (coexpressing MHCIIa and MHCIId/x); and 3) single fiber dissection from SHR soleus yielded a lower proportion of type I fibers, a higher proportion of fast-twitch fibers (types IIA and IIA+IID), and a higher proportion of hybrid fibers (types I+IIA and IIA+IID) than the homologous muscles from the age-matched WKY rats. Because the presence of hybrid fibers is viewed as a marker of muscle transformation, these data suggest that SHR soleus undergoes transformation well into adulthood. Our data show also that, for a given fiber type, there are no significant differences between SHR and WKY soleus muscles with respect to any of the Ca2+-activation properties examined. This finding indicates that the lower specific tensions reported in the literature for SHR soleus muscles are not due to strain- or hypertension-related differences in the function of the contractile apparatus or regulatory system.

Altered muscle metabolism associated with vasoconstriction in spontaneously hypertensive rats

In the rat muscle vascular bed, vasoconstrictors either increase or decrease oxygen consumption (VO2). The present study compared the effects of norepinephrine (NE), angiotensin II (ANG II), and 5-hydroxytryptamine (5-HT) on vasoconstriction-associated metabolism in the constant-flow perfused hindlimb of spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) in the absence of insulin. Basal perfusion pressure, VO2, glucose uptake, and lactate production were increased by 21.4, 11.9, 46.4, and 44.9% (P < 0.05 for all), respectively, in SHR, which also had higher blood pressure and metabolic rate (P < 0.05) in vivo. Dose-response curves for NE-induced perfusion pressure, VO2, and lactate production in SHR were shifted to the left compared with WKY. Associated with the increased perfusion pressure, NE-induced VO2 and glucose uptake were both decreased (P < 0.01), particularly at high concentrations. These differences were unaffected by 10 microM propranolol but were all diminished by further addition of prazosin (2.5 nM). ANG II stimulated VO2, glucose uptake, and lactate production in both strains, but the increased lactate production was smaller in SHR (P < 0.05) with a proportional decrease (P < 0.05) in glucose uptake. Conversely, 5-HT decreased VO2 in both strains (P < 0.01), and this effect was greater in SHR (P < 0.01). These data suggest that SHR muscle thermogenesis and glucose uptake are impaired during vasoconstriction, especially in response to NE.

Intracellular free Ca2+ and basal Mn2+ influx in cultured aortic smooth muscle cells from spontaneously hypertensive and normotensive Wistar-Kyoto rats

Numerous studies investigating the possible role of altered Ca2+ homeostasis in hypertension have compared resting and agonist-stimulated intracellular free Ca2+ ([Ca2+]i) in cultured aortic smooth muscle cells from spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats. However, such studies have not given consistent results. Differences in the method used to load cells with the Ca(2+)-sensitive indicator fura-2 have been investigated here as a possible source of variability between studies. We also describe the adaptation of a fluorescence technique for the assessment of basal Ca2+ permeability in SHR and WKY through the measurement of Mn2+ influx. The results are consistent with the hypothesis that basal Ca2+ influx is elevated in cultured aortic smooth muscle cells from SHR compared to those from WKY. However, this was not reflected as a significant difference between the two strains in basal or angiotensin II (200 nmol/L)-stimulated [Ca2+]i. Furthermore, this result was not dependent on the protocol used to load cells with fura-2. Hence, measurement of bulk [Ca2+]i does not appear to be the most sensitive parameter for altered Ca2+ homeostasis in SHR. Other compartments of the cell may better reflect altered Ca2+ fluxes in hypertension and are discussed in this work.

Changes in angiotensin II receptor density and calcium handling during proliferation in SHR aortic myocytes

The aim of the present work was to characterize angiotensin II (ANG II) receptors and their effect on intracellular free Ca2+ concentration ([Ca2+]i) in proliferating aortic smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Independently from the proliferating state of cultures, apparent affinities of ligands (ANG II > losartan > > CGP-42112A) were consistent with the presence of AT1 receptors in primary cells from SHR and WKY. In proliferating cultures, increases in [Ca2+]i elicited by ANG II (100 nM) were dramatically attenuated or abolished in VSMCs from both strains compared with confluent and postconfluent cultures. Ca2+ releases induced by ionomycin and by ANG II in the absence of extracellular Ca2+ were also impaired in proliferating cultures. In addition, no significant strain difference was found in proliferating cultures with respect to ANG II receptor density, basal [Ca2+]i, and ANG II-induced increases in [Ca2+]i. However, ANG II receptor density significantly increased in SHR, but not in WKY VSMCs at postconfluence. Furthermore, basal [Ca2+]i was elevated in confluent and postconfluent cultures from SHR but not WKY. In confluent cultures, ANG II- and ionomycin-induced Ca2+ releases were enhanced in SHR VSMCs compared with WKY VSMCs. These results show that ANG II-induced Ca2+ release and ionomycin-sensitive Ca2+ stores are enhanced in SHR VSMCs but dramatically decreased in proliferating VSMC cultures from both strains. Mechanisms underlying these alterations remain to be defined. However, the results suggest that alterations in ANG II AT1 receptor density and in intracellular Ca2+ handling in confluent and postconfluent cultures are not associated with the proliferative phenotype of SHR VSMCs. In addition, no evidence for any change in ANG II receptor subtype associated with proliferation of VSMCs was found in either strain.

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

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

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

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

Increased sodium-dependent D-glucose transport in the jejunal brush-border membrane of spontaneously hypertensive rat

The current studies explore the effect of hypertension on D-glucose transport into jejunal brush-border membrane vesicles (BBMV). Spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats, as a control group, were used. The purity of the BBMV from both groups of animals was validated by the finding that the specific activity of brush-border enzyme marker, sucrase, was severalfold greater in membrane vesicles compared with corresponding values in mucosal homogenate. D-glucose uptake was Na+ dependent in both groups of animals, with a transient increase in the intravesicular concentration of D-glucose. However, the initial rate and the magnitude of the accumulation of Na+-dependent D-glucose was significantly higher in SHR compared with WKY rats. In order to investigate the mechanism(s) for the increase in Na+-dependent D-glucose transport in SHR, several experiments were performed: (1) an experiment that indicated 22Na uptake, as an indicator for Na+ permeability, was similar between SHR and WKY rats, (2) kinetic studies that indicated that Vmax values of SHR were significantly greater that those of WKY rats. In contrast, similar Km values for glucose were found between SHR and WKY rats, (3) Na+-dependent phlorizin binding measurements that were not altered by hypertension and (4) a study of the brush-border membrane lipid composition that showed a significant increase in the free cholesterol/phospholipid ratio in SHR. We conclude that altered membrane cholesterol content and consequently altered lipid fluidity could be, at least in part, responsible for the observed increase in Na+-dependent D-glucose transport in SHR.

Comparison of 11 beta-hydroxysteroid dehydrogenase in spontaneously hypertensive and Wistar-Kyoto rats

11 beta-Hydroxysteroid dehydrogenase (11 beta-HSD) modulates glucocorticoid interactions with mineralocorticoid and glucocorticoid receptors in vivo, by converting 11 beta-hydroxyglucocorticoids to their inactive 11-ketone derivatives. Defective 11 beta-oxidation of glucocorticoids has been associated with hypertension. The objective of this study was to investigate whether 11 beta-HSD contributes to the occurrence of hypertension in spontaneously hypertensive rats (SHRs). The liver and kidney microsomal oxidations of corticosterone (the physiological glucocorticoid in rats) in organs from juvenile (3 weeks old) and adult (3 months old) SHR and Wistar-Kyoto (WKY) rats, with NAD and NADP, show no differences between rat strains. For cortisol, with NADP, adult SHRs show (1.3-3 times; P < 0.05) lower kidney microsomal oxidation rates. The liver microsomal reduction of cortisone shows remarkable interstrain differences; with NADH, reduction is conducted only by adult WKY rats, whereas with NADPH, juvenile animals show similar reduction rates, but at adulthood, only WKYs reduce cortisone. Using Western blot analysis with antibodies against 11 beta-HSD1, positive signals are obtained only for liver microsomes, appearing somewhat lower in SHRs for juvenile but not adult animals. Urinary corticosterone/11-dehydrocorticosterone ratios (measured in adult animals) are not different between rat strains, but are elevated after administration of corticosterone in both strains (although significant only in SHRs). The data provide no indications for exaggerated stimulation of renal corticosteroid receptors, due to modified 11 beta-HSD, in SHRs. However, the experiments suggest the existence of multiple 11 beta-HSDs, in addition to 11 beta-HSD1 and 11 beta-HSD2, some of which may be modified in SHR, but the nature and physiological role of these 11 beta-HSDs is unclear.

Peritoneal macrophages from stroke-prone spontaneously hypertensive rats accumulate more cholesteryl ester than do macrophages from Wistar-Kyoto rats

The intracellular cholesterol metabolism of peritoneal macrophages from stroke-prone spontaneously hypertensive rats (SHRSP) was compared to that of normotensive Wistar-Kyoto rats (WKY) in order to examine the role of macrophages in the development of arterial fat deposits in the SHRSP. Scavenger receptor activity and intracellular acyl CoA:cholesterol acyltransferase (ACAT) activity were significantly higher in macrophages from SHRSP compared to findings in WKY, in the presence of modified low-density lipoprotein (LDL), acetylated-LDL (Ac-LDL). Moreover, macrophages from the SHRSP accumulated more cholesteryl ester than seen in WKY in response to Ac-LDL. ACAT activity and cholesteryl ester accumulation were inhibited by specific ACAT inhibitor, HL-004, to a similar extent, in macrophages from WKY and SHRSP. These findings suggest the susceptibility of SHRSP to arterial fat deposits.

Time-dependent changes in catecholamine turnover in spontaneously hypertensive rats exposed to hypoxia

In three separate experiments, 4 to 5-week-old spontaneously hypertensive rats (SHR) and normotensive controls (Wistar-Kyoto [WKy]) were exposed to hypobaric hypoxia (simulated altitude = 3658 m) for 3 hr, 3 days, or 3 weeks. Comparable groups were maintained in ambient laboratory conditions (normoxia). Hypoxia prevented the increase in blood pressure noted in 8-week-old normoxic SHR. Right ventricular hypertrophy first occurred after 3 days of hypoxia, and was found in both SHR and WKy. Catecholamine turnover was measured using the tyrosine hydroxylase inhibitor, alpha-methyl-p-tyrosine. In myocardium, both strains evidenced hypoxia-induced changes in norepinephrine (NE) turnover, which was increased at 3 hr, normalized at 3 days, and increased again at 3 weeks. Reduced basal NE concentration at 3 days indicated a temporary deficit in synthetic capacity, which would allow maintenance of a heightened neuronal output. Catecholamine turnover in right and left ventricles differed little in response to hypoxia, in spite of differential hemodynamic demands on SHR versus WKy or on right versus left ventricle. In contrast to findings in myocardium, significant interactive effects between strain and altitude exposure were noted for adrenal catecholamine turnover. Specifically, hypoxia exerted a suppressive influence in SHR that was not evident in WKy, and this may represent an important component of hypoxia-induced protection against the development of spontaneous hypertension.

Regulation of neuronal nitric oxide synthase in rat adrenal medulla

Neuronal nitric oxide synthase (nNOS) has been suggested to be involved in cardiovascular homeostasis. We studied the regulation of nNOS expression, determining nNOS mRNA expression levels in various tissues in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). We also investigated the effects of antihypertensive treatment with the angiotensin II antagonist hydralazine or reserpine on nNOS mRNA expression. The expression levels of nNOS mRNA and nNOS protein were determined by Northern and Western blot analysis, respectively. NADPH-diaphorase histochemistry was used to identify cells in the adrenal medulla that expressed nNOS. No significant differences in expression levels in SHR and WKY were observed in the cerebellum and brain stem. nNOS mRNA expression levels in the decapsular portion of the adrenal gland were developmentally modulated and in a 24-week-old WKY were 2.5 times higher than in an age-matched SHR. This reduced expression of nNOS mRNA in the decapsular portion of the adrenal gland of SHR seemed to be a result of hypertension in the SHR, because administration of either an angiotensin II antagonist (TCV-116) or hydralazine upregulated nNOS mRNA expression in both SHR and WKY. Marked augmentation of nNOS mRNA expression in the decapsular portion of the adrenal gland by reserpine treatment suggested an intimate relation between nNOS in the decapsular portion of the adrenal gland and the sympathoadrenal system. Reserpine treatment also increased the expression of nNOS protein; however, reserpine treatment did not affect the distribution pattern of nNOS-positive cells (NADPH-diaphorase-positive cells) in the adrenal medulla.(ABSTRACT TRUNCATED AT 250 WORDS)

Na(+)-H+ exchanger expression in vascular smooth muscle of spontaneously hypertensive and Wistar-Kyoto rats

The Na(+)-H+ exchanger has important modulatory effects on vascular smooth muscle cell proliferation and contractility. Increased Na(+)-H+ exchange activity is a general property of many tissues, including mesenteric artery and cultured vascular smooth muscle cells, in the spontaneously hypertensive rat (SHR). In the present work, we investigated whether alterations in the steady-state levels of specific Na(+)-H+ exchanger mRNA isoforms (NHE-1 through NHE-4) are associated with the observed increases in exchanger activity. Poly(A+) mRNA prepared from 12-week-old hypertensive SHR and normotensive Wistar-Kyoto (WKY) aorta, kidney, and intestine was hybridized to cDNAs specific for each NHE isoform. By Northern blot analysis, NHE-1 was detected in all tissues as well as cultured vascular smooth muscle cells and was not regulated differently in SHR compared with WKY tissues. There was no expression of NHE-2, NHE-3, or NHE-4 in SHR and WKY aortas or in cultured vascular smooth muscle cells from SHR and WKY aortas. Stimulation of NHE-1 mRNA expression by growth factors was similar in cultured SHR and WKY vascular smooth muscle cells. We conclude that the previously observed increase in exchanger activity in blood vessels and cultured vascular smooth muscle cells of the SHR is not caused by induction of the NHE-2, NHE-3, and NHE-4 isoforms or by alterations in steady-state NHE-1 mRNA expression. These findings suggest that posttranslational regulation of the Na(+)-H+ exchanger is responsible for increased activity in the SHR.

Release of nitric oxide in response to acetylcholine is unaltered in spontaneously hypertensive rats

OBJECTIVE

Although a decreased responsiveness to acetylcholine, an endothelium-dependent vasodilator, has been reported in arteries isolated from spontaneously hypertensive rats (SHR), the precise role of nitric oxide (NO) in the in vivo regulation of blood pressure is not clear. We investigated the effects of acetylcholine and of NG-nitro-L-arginine methyl ester (L-NAME), an NO synthase inhibitor, on mean arterial pressure and the production of NO metabolites (nitrate and nitrite) in SHR and in Wistar-Kyoto (WKY) rats, their normotensive control strain.

DESIGN

We determined serum levels of nitrate and nitrite before and after the intravenous injection of 40 micrograms/kg acetylcholine following the administration of L-NAME (30 mg/kg) or its vehicle in adult SHR and WKY rats.

RESULTS

Acetylcholine administration significantly reduced mean arterial pressure in both SHR and WKY rats, accompanied by a significant rise in serum nitrate and nitrite. Administration of L-NAME significantly increased the mean arterial pressure in SHR and in WKY rats. L-NAME inhibited the hypotension induced by acetylcholine and the rise in serum nitrate and nitrite both in SHR and in WKY rats.

CONCLUSION

The release of NO stimulated by acetylcholine was unaltered in SHR, supporting previous in vitro results.

A deficit in preprodynorphin mRNA expression in hippocampus of spontaneously hypertensive rats

A significantly lower level of preprodynorphin mRNA hybridization signal was found in hippocampal dentate granule cells of spontaneously hypertensive rats at 4 and 16 weeks old, before and after hypertension development respectively, when compared with preprodynorphin (PPD) mRNA level in the hippocampus of age-matched Wistar-Kyoto rats. The possible implications of disturbed PPD mRNA and dynorphin expression in the hippocampus are discussed with regard to pathophysiology of hypertension and central control of cardiovascular function.

Different calcium storage pools in vascular smooth muscle cells from spontaneously hypertensive and normotensive Wistar-Kyoto rats

OBJECTIVE

To evaluate whether the distribution of intracellular free calcium may be impaired in primary hypertension.

DESIGN

Cytosolic free calcium and stored calcium were investigated in cultured vascular smooth muscle cells from spontaneously hypertensive rats (SHR).

METHODS

The concentrations of intracellular and stored calcium were investigated in cultured vascular smooth muscle cells from spontaneously hypertensive rats aged 6 months from the Münster strain (SHR) and from age-matched normotensive Wistar-Kyoto (WKY) rats. Vascular smooth muscle cells were grown on coverslips, and fluorescence measurements of the intracellular calcium concentration were performed using fura-2. The different effects of thapsigargin, a selective Ca-ATPase inhibitor, and of angiotensin II (Ang II) on the calcium storage pools were investigated.

RESULTS

In the absence of external calcium thapsigargin produced a dose-dependent transient increase in the concentration of intracellular calcium in vascular smooth muscle cells. The thapsigargin-induced maximum peak increase in the concentration of intracellular calcium was not significantly different in SHR and WKY rats. After depletion of the thapsigargin-sensitive calcium pools the addition of 100 nmol/l Ang II produced a rise in the concentration of intracellular calcium in vascular smooth muscle cells from SHR and WKY rats. Using vascular smooth muscle cells from the SHR the Ang II-induced increase in the concentration of intracellular calcium was not significantly different in the presence and absence of thapsigargin, indicating that the calcium pools depleted by thapsigargin and Ang II do not overlap significantly in vascular smooth muscle cells from SHR. In contrast, in the WKY rats the response to Ang II was significantly diminished after depletion of the thapsigargin-sensitive pool. When Ang II and thapsigargin were administered in the reverse order, i.e. Ang II before thapsigargin, the thapsigargin response was diminished in the WKY rats but not in the SHR.

CONCLUSION

SHR differ from WKY rats in having vascular smooth muscle cells that contain thapsigargin-sensitive calcium storage pools that are distinct from the Ang II-sensitive calcium pools.

Heparin suppresses endothelin-1 peptide and mRNA expression in cultured endothelial cells of spontaneously hypertensive rats

Heparin given sc consistently lowers blood pressure in spontaneously hypertensive rats (SHR). This study was designed to examine heparin's effect on vasoconstrictor endothelin-1 production in cultured aortic endothelial cells (EC). Aortic EC from SHR and normotensive Wistar Kyoto rats (WKY) were cultured and incubated with or without different concentrations of heparin. Heparin suppressed endothelin-1 release and endothelin-1 mRNA expression in a dose- and a time-dependent fashion in both WKY and SHR. The suppressive effects were more augmented in SHR than in WKY: SHR versus WKY--endothelin-1 level at 6 h = 8 +/- 1.8 versus 14 +/- 2.2 pg/10(6) cells (P < 0.01) and mRNA expression--85 versus 52% maximal inhibition by heparin, 10 U/mL (=70 micrograms/mL) (P < 0.01). When heparin was added with transcriptional inhibitor actinomycin D and incubated for 30 min, no further inhibition of endothelin-1 mRNA level measured after another 30 minutes was observed compared with the endothelin-1 mRNA level in cultured EC of SHR treated with just actinomycin D at 30 min. These results suggest that heparin regulates endogenous endothelin-1 production by cultured EC, probably at the transcriptional level, and that this effect is more marked in SHR than in WKY.

Anterior pituitary proopiomelanocortin expression is decreased in hypertensive rat strains

Studies comparing neuroendocrine differences between the spontaneously hypertensive rat (SHR) and the normotensive Wistar-Kyoto (WKY) strains have suggested altered anterior pituitary corticotrope expression of POMC associated with the development of hypertension in SHR animals. One major difficulty in comparing the SHR and WKY strains is that the two strains exhibit genetic differences unrelated to blood pressure status, because inbred in the SHR genome is a profile of behavioral characteristics different from those in the WKY, including hyperactivity in a novel environment and hyperreactivity in responding to stress. The present studies examine two new inbred rat strains, the WKHT and WKHA, which independently express the hypertension and behavioral traits, respectively. Together with the SHR and WKY, these genetically related, homozygous strains permit a more definitive means of examining the neuroendocrine correlates of either hypertension or behavior. The adult (5-month-old) male anterior pituitary gland content of the POMC peptides beta-endorphin and ACTH was decreased approximately 50% in the SHR and WKHT strains compared to that in the WKY strain, whereas hormone levels in the WKHA strain were not significantly different from those in the WKY strain. Reduced POMC peptide levels were, therefore, specifically associated with the hypertensive trait. Hormone content in prehypertensive weanling (5- to 7-week-old) SHR and WKHT animals was also reduced approximately 35% compared to that in WKY animals. Northern blot analysis identified a 45% decrease in POMC mRNA expression in the hypertensive SHR and WKHT strains, which paralleled the changes in tissue hormone content. Using both immunocytochemistry and in situ hybridization histochemistry, the number of labeled cells per unit area of tissues section was reduced approximately 45% in anterior pituitary tissues from SHR and WKHT rats compared to that in WKY tissues. The levels of POMC mRNA per cell, determined by quantitative densitometry, were not statistically different in the anterior pituitaries of WKHT, SHR, and WKY rats. The decrease in hormone content and POMC mRNA levels may, thus, reflect decreased anterior pituitary gland corticotrope populations. Although POMC peptide levels in the anterior pituitaries of adult WKHA animals were not significantly different from those in WKY animals, the morphological studies demonstrated a 30% increase in the corticotrope population in the WKHA strain. In contrast, POMC mRNA levels in WKHA animals were decreased 30%, and the amount of POMC mRNA per corticotrope was decreased approximately 35% compared to that in WKY, SHR, and WKHT tissues.(ABSTRACT TRUNCATED AT 400 WORDS)

Chronobiologic evaluation of angiotensin-converting enzyme activity in serum and lung tissue from normotensive and spontaneously hypertensive rats

Angiotensin-converting enzyme (ACE) activity in serum and lung tissue from both normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) was determined at six different circadian times. In WKY rats serum ACE varied significantly within 24 h, mainly due to reduced enzyme activity at 12:00 h. In SHR the 24-h profile of serum ACE did not exhibit time-dependent differences. Mean serum ACE activity over 24 h was significantly higher in WKY than in SHR. In lung tissue ACE activity did not depend on the circadian time in either strain. Mean enzyme activity in lung tissue was not different between WKY and SHR. We conclude that circadian changes in the activity of serum and tissue ACE are unlikely to play an important role in the regulation of the circadian blood pressure profile in both normotensive and spontaneously hypertensive rats.

Production of nerve growth factor by cultured vascular smooth muscle cells from spontaneously hypertensive and Wistar-Kyoto rats

OBJECTIVE

Nerve growth factor (NGF) is a neurotrophic protein which acts on peripheral sympathetic nerves. Elevated NGF in vascular tissues of young spontaneously hypertensive rats (SHR) has been reported. The aim of the present study was to compare the amount of NGF secreted from cultured vascular smooth muscle cells (VSMC) and mesenteric artery and thoracic aorta segments from SHR and Wistar-Kyoto (WKY) rats.

METHODS

VSMC prepared by the enzyme digestion method from the thoracic aortic media of 14-week-old SHR and age-matched WKY rats were subcultured in Dulbecco's modified Eagle's medium containing 10% fetal calf serum. Segments of mesenteric artery and thoracic aorta from 4-week-old SHR and age-matched WKY rats were similarly cultured. The NGF content in conditioned medium was measured using an enzyme immunoassay. The protein content of VSMC was measured by the Lowry method.

RESULTS

Total NGF content in the cell culture medium was increased during an exponential growth phase and then gradually decreased during a quiescent phase in both rat strains. There were no significant differences in the levels of NGF secreted from mesenteric artery and thoracic aorta segments between the SHR and WKY rats. The differences in cellular protein content between SHR and WKY rats were very small.

CONCLUSIONS

In contrast to the reports of increased NGF in SHR tissues, our data demonstrate that NGF secretion was lower in VSMC from SHR, and was equivalent in mesenteric artery and thoracic aorta segments from SHR and WKY rats. We have no clear explanation for these observations, but the present results indicate that upregulation of NGF in SHR tissues is not responsible for a simple enhancement of NGF synthesis in VSMC, and suggest a breakdown of the regulatory mechanism or mechanisms of NGF gene expression in SHR tissues.

Developmental differences of angiotensinogen mRNA in the preoptic area between spontaneously hypertensive and age-matched Wistar-Kyoto rats

In order to know the possible involvement of the central angiotensin system in hypertension, angiotensinogen mRNA (AomRNA) levels of eight discrete brain areas were measured by Northern blot hybridization analysis in the spontaneously hypertensive rats (SHR), compared with those in age-matched normotensive Wistar-Kyoto rats (WKY). In 16-week-old SHR (hypertensive stage), AomRNA levels in the preoptic area (POA), but not in the ventromedial hypothalamus, lateral hypothalamus and mammillary body, among the hypothalamic nuclei, were higher (approximate 50%) than in WKY. There were no differences in other brain areas, such as the striatum, septum, amygdala and cerebellum between both the strains. The AomRNA levels in POA were already higher (38%) in 4-week-old SHR (prehypertensive stage) without significance, and the difference was augmented (82%) in 7-week-old SHR (evolving stage). These results suggest that the developmental changes of AomRNA levels at POA may be related in some aspect to hypertension process.

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

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

Angiotensin converting enzyme variability in hypertensive and normotensive rats

Recent data have revealed biological and genetic variability in normotensive Wistar-Kyoto rats, which are considered to be the most appropriate control strain for spontaneously hypertensive rats. To investigate the possibility that angiotensin converting enzyme activity could be affected by this variability, we measured plasma and tissue (lung, heart, renal cortex, renal medulla, and adrenal gland) angiotensin converting enzyme activity in spontaneously hypertensive rats and normotensive Wistar-Kyoto rats from three commercial suppliers in France: Iffa-Credo, Janvier, and Charles River Laboratories. Angiotensin converting enzyme activity was measured in vitro with a fluorometric assay using carbobenzoxy-Phe-His-Leu as substrate. Angiotensin converting enzyme activity in both rat strains varied considerably from one supplier to another, and therefore, comparisons of spontaneously hypertensive rats and Wistar-Kyoto rats from the different suppliers produced conflicting results. For Wistar-Kyoto rats, angiotensin converting enzyme activity in the plasma, heart, kidney, and adrenal glands was highest in rats from Iffa-Credo and lowest in rats from Charles River. For spontaneously hypertensive rats, angiotensin converting enzyme activity in the plasma and tissues was highest in rats from Janvier, whereas no difference could be observed between rats from Iffa-Credo and Charles River. These data confirm the problem of how to interpret and compare studies that use spontaneously hypertensive and Wistar-Kyoto rat strains.

Type I collagen synthesis in cultured aortic smooth muscle cells from spontaneously hypertensive rats and normotensive control, Wistar-Kyoto rats

An inhibition ELISA was used to quantify the amount of type I collagen synthesized in culture media and cell layers from aortic smooth muscle cells (SMCs) of spontaneously hypertensive rats (SHR) and normotensive control, Wistar-Kyoto rats (WKY). Cultured cells were also observed by electron microscopy. Collagen content in the culture media was strongly increased after 6 days in both cultures. Collagen and protein contents in the medium and cell layer from SHR were significantly higher than those in WKY at day 14. However, cell density in SHR-derived cells was also higher than that of WKY. No significant differences were detected in the rates of collagen content between SHR and WKY on a per cell basis. The main differences between SHR and WKY in collagen and protein levels may be due to the greater number of SHR cells and increased amounts of extracellular matrix components. The assay system outlined here should be useful for studying the control of extracellular-matrix synthesis.

Altered pineal adrenergic-stimulated cyclic nucleotide responses in spontaneously hypertensive rats

In this study, we examined the pineal adrenergic-stimulated cyclic nucleotide responses in spontaneously hypertensive rats (SHR) and their genetic control, Wistar-Kyoto rats (WKY). Treatment with norepinephrine stimulated cAMP and cGMP contents up to 50- and 12-fold in WKY pinealocytes, compared with a 35- and 4-fold increase in SHR. By contrast, there was no difference in the isoproterenol-stimulated cAMP and cGMP contents, suggesting a reduced alpha 1-adrenergic potentiation of beta-adrenergic-stimulated cGMP response in SHR pinealocytes. The altered potentiation mechanism was examined using agents that activate protein kinase C or elevate intracellular Ca2+. In the presence of a protein kinase C activator, the isoproterenol-stimulated cAMP response was potentiated to a similar degree in WKY and SHR pinealocytes. In contrast, the potentiating effects of ionomycin and KCl on the isoproterenol-stimulated cAMP and cGMP responses in SHR pinealocytes were markedly reduced. These results indicate that in the SHR pineal gland, an altered intracellular Ca(2+)-mediated event may account for the reduction in alpha 1-adrenergic potentiation of beta-adrenergic-stimulated cyclic nucleotide responses.

Sucrose drinking reduces dorsal hypothalamic beta-endorphin levels in spontaneously hypertensive rats but not in Wistar-Kyoto rats

The present study was performed to test whether drinking of a 10% sucrose solution would preferentially alter tissue content of beta-endorphin in dorsal and ventral hypothalamic fragments from the spontaneously hypertensive rat (SHR), as opposed to the Wistar-Kyoto rat (WKY). Changes were correlated with cardiovascular function and circulating catecholamine levels to assess the role of hypothalamic beta-endorphin, a putative mediator of sucrose-induced changes in cardiovascular sympathetic nervous tone. Male rats were trained to consume their total 24-h water intake in a single period between 0900-1100 h. Catheters were chronically implanted to sample blood and to record arterial blood pressure and heart rate. The experimental protocol consisted of a recording session, which included a 10-min drinking period wherein rats consumed 8 ml of either sucrose solution or deionized water. Rats were sacrificed and hypothalami removed for analysis of beta-endorphin content. Comparable increases in blood pressure were noted in SHR and WKY during drinking of either sucrose or water. Drinking-induced tachycardia was blunted in SHR drinking sucrose. Plasma norepinephrine was increased only in sucrose-drinking SHR. Plasma glucose levels were elevated in both SHR and WKY following drinking of sucrose, but not water. beta-Endorphin levels were reduced (p < 0.05) in dorsal, but not ventral, hypothalamic fragments only in SHR drinking sucrose. The sucrose-induced changes in beta-endorphin did not correlate with blood pressure responses. The results indicate an exaggerated stimulation of beta-endorphin release in the dorsal hypothalamus following sucrose ingestion in SHR.

Angiotensin-II induction of plasminogen activator inhibitor-1 gene expression in astroglial cells of normotensive and spontaneously hypertensive rat brain

Angiotensin-II (AII) stimulates plasminogen activator inhibitor-1 (PAI-1) gene transcription, translation, and protein secretion from astroglial cells derived from normotensive [Wistar-Kyoto (WKY)] rat brain, an effect mediated by AII type 1 (AT1) receptors. Since abnormal expression of the brain AII system has been demonstrated in spontaneously hypertensive (SH) rats, we investigated the regulation of PAI-1 gene expression by AII in astroglial cells from the brains of these animals. AII caused an increase in PAI-1 gene expression in SH rat astroglia in a manner similar to that observed in WKY-derived cultures. However, both the basal and AII-stimulated levels of PAI-1 mRNA in SH rat astroglia were only 20% of those observed in WKY rat astroglial cultures. Consequently, there was a significant reduction in the de novo synthesis and secretion of PAI-1 from astroglia of SH rat brain. The reduced synthesis and secretion of PAI-1 from SH rat brain astroglia was associated with lower numbers of AT1 receptors in these cells. However, the steady state levels of AT1 receptor mRNA were comparable in both WKY and SH rat astroglia. This reduction in AII-modulated PAI-1 levels in SH rat astroglia is consistent with a proposed role of these interactions in the development of hypertension in these animals.

Proteoglycan synthesis in normotensive and spontaneously hypertensive rat arteries in vitro

Proteoglycans (PGs) were analyzed and compared in the media of the thoracic aorta, abdominal aorta, left carotid artery and superior mesenteric artery of age-matched Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Two ages were examined; 10 week old, during the development of hypertension and 28 week old, when hypertension is well established in the SHR. Large chondroitin sulfate PG, large heparan sulfate PG and biglycan (PGI) and decorin (PGII) small PGs were identified. Biglycan was the predominant small PG found in all arteries. Newly synthesized PGs were labelled in vitro with 35SO4 for quantitation. The synthesis of large and small PGs was similar in the media of the thoracic aorta, abdominal aorta, left carotid artery, and superior mesenteric artery. The large to small ratio value, a measure of the artery PG composition, was also similar among the four arteries but was highest in the mesenteric artery. In both WKY and SHR arteries there was significantly decreased PG synthesis in the 28-week old compared to 10-week old animals. This was especially true for large PG. Hypertensive changes in PG synthesis were seen mainly in the carotid artery. In this artery, synthesis of both large and small PG was increased in the SHR, at both ages. The ratio of large to small PG was not significantly different between SHR and WKY arteries. We conclude that 28-week old WKY and SHR rat arteries synthesize less large and small PG than 10-week old arteries. The most prominent change seen in hypertensive rats is an increase in PG synthesis in the carotid artery.

Expression of natriuretic peptide genes in cardiac tissues of hypertensive rats

A quantitative assay using a reverse transcriptase-linked polymerase chain reaction has been developed for measuring the levels of rANP and iso-rANP mRNA. A linear correlation between total RNA template and amplified cDNA was obtained for the amplification of cDNA from both iso-rANP and rANP mRNAs even when both cDNAs were amplified in the same assay. Application of the assay showed that in contrast to rANP levels of iso-rANP transcript in hypertensive rats remained approximately the same in atrium but were increased 10-fold in ventricle compared to normal rats. Given the relative size of the ventricle the increase of iso-rANP in this tissue in SHR may be a major response to the hypertensive state.

Influence of dietary protein on glomerular angiotensin II-receptor binding in normotensive and spontaneously hypertensive rats

1. The binding of angiotensin II to glomerular receptors was studied in spontaneously hypertensive and normotensive Wistar-Kyoto rats in response to 7, 16 and 32% isocaloric, isonatraemic protein diets. 2. Increased dietary protein elevated the systemic angiotensin II levels of both spontaneously hypertensive and Wistar-Kyoto rats [F0.05(2,26) = 4.758, P less than 0.05; n = 36], and this was not associated with changes in either systemic blood pressure or cortical renin activity. 3. Furthermore, no significant changes in the affinity or density of angiotensin II receptors were associated with changes of dietary protein intake in either strain. 4. These results indicate a dissociation between the system renin-angiotensin system and the tissue renin-angiotensin system in response to protein intake.

cGMP pathway and mechanical properties of carotid artery wall in WKY rats and SHR: role of endothelium

We measured the static mechanical properties and tissue guanosine 3',5'-cyclic monophosphate (cGMP) content in the carotid artery of 16- to 18-wk-old Wistar-Kyoto (WKY) rats and age-matched spontaneously hypertensive rats (SHR). Carotid compliance (CC) and tissue cGMP measurements were performed under control conditions with intact endothelium (E+), after local incubation with methylene blue (10(-5) M, 20 min), and after mechanical removal of the endothelium (E-). Under control conditions, CC was lower in SHR than in WKY rats (P less than 0.01) and carotid cGMP level was higher in SHR than in WKY rats (30.34 +/- 3.69 vs. 19.72 +/- 2.28 fmol/mg tissue; P less than 0.02). Methylene blue induced no significant change in CC in both strains and produced a similar decrease in carotid cGMP in WKY rats by 88% (P less than 0.001) and in SHR by 94% (P less than 0.001). Endothelium removal induced a similar increase in CC relative to control conditions (P less than 0.01, in both strains) but reduced cGMP content by 28% in WKY rats (P less than 0.02) and by 90% in SHR (P less than 0.001), i.e., a significantly higher reduction in SHR than in WKY rats (P less than 0.001). Despite a higher vasomotor tone, the "cGMP pathway" seems to be more activated in the SHR than in the WKY rat. Our results suggest that the mechanism involved in cGMP synthesis regulation in the SHR is endothelium dependent. This may be interpreted as an insufficient endothelium-dependent compensatory phenomenon of local regulation against genetic abnormalities.

Corticosterone 6 beta-hydroxylation correlates with blood pressure in spontaneously hypertensive rats

Evidence for increased glucocorticoid 6 beta-hydroxylation (enhanced family 3A cytochrome P-450 activity) is found in certain reversible forms of human hypertension. This association was investigated in the spontaneously hypertensive rat (SHR). The proportion of injected [3H]corticosterone excreted in urine as 6 beta-[3H]OH-corticosterone was four- to fivefold higher in SHR than in control Wistar-Kyoto rats, before and after development of overt hypertension. Both hypertension and 6 beta-hydroxylation were inhibited by troleandomycin (a selective inhibitor of family 3A cytochromes P-450), consistent with a role for increased steroid 6 beta-hydroxylation in the genesis of hypertension in the SHR.

Liver mevalonate 5-pyrophosphate decarboxylase is responsible for reduced serum cholesterol in stroke-prone spontaneously hypertensive rat

Spontaneously hypertensive rat (stroke-prone) (SHRSP) has an interestingly low serum cholesterol level due to a reduced biosynthesis of cholesterol in the liver (Iritani, N., Fukuda, E., Nara, Y., and Yamori, Y. (1977) Atherosclerosis 28, 217-222). In this study, we examined the mechanism underlying the reduction of hepatic cholesterol biosynthesis in the rat. Our initial findings in SHRSP, as compared with normotensive Wistar Kyoto rat (WKY), showed that 1) the incorporation of [14C]acetate into cholesterol in the liver slices was markedly less, 2) 3-hydroxyl-3-methylglutaryl (HMG) CoA reductase activity was not reduced, and 3) the incorporation of [3H]mevalonic acid into both cholesterol and squalene was significantly less. The above initial findings suggested that the reduction in the hepatic cholesterol biosynthesis took place in one or more enzymatic processes starting with mevalonic acid and continuing to squalene. When the incorporation of [3H]mevalonic acid into phosphomevalonate derivatives was studied using an ion exchange column, only the radioactivity incorporated into isopentenyl-pyrophosphate (isopentenyl-PP) was less in SHRSP. Furthermore, the specific activity of diphosphomevalonate (mevalonate-PP) decarboxylase in the liver-soluble fractions was reduced 50% in SHRSP as compared with WKY. Kinetic studies using liver crude extracts indicated a lower Vmax value in SHRSP (SHRSP, 0.47; WKY, 2.05 nmol/min/mg), and an unchanged Km value (SHRSP, 18.2; WKY, 19.6 microM). The activity of mevalonate-PP decarboxylase was also found to be reduced in other tissues, including the brain, testis, small intestine, and cultured vascular smooth muscle cells. From the above observations, we concluded that the lower activity of mevalonate-PP decarboxylase was responsible for the reduced cholesterol biosynthesis in the liver of SHRSP.

Diminished phospholipase C activation by dopamine in spontaneously hypertensive rats

It is reported that a defect in dopamine-1 (DA-1) receptor adenylate cyclase coupling in the proximal convoluted tubule in the spontaneously hypertensive rat may contribute to the diminished natriuretic response to DA-1 receptor agonists. Since the tubular DA-1 receptor is also coupled to phospholipase C, and both of these cellular signaling processes are involved in DA-1 receptor-mediated diuresis and natriuresis, it is important to know whether a similar defect is also present in DA-1 receptor-coupled phospholipase C pathway. The present study was therefore designed to determine the functional status of DA-1 receptor-phospholipase C coupling system of adult spontaneously hypertensive rats using a renal cortical slice preparation. In addition, the renal response to exogenously administered dopamine (1 microgram/kg/min i.v.) was also determined. We found that basal phospholipase C activity was significantly higher in hypertensive rats than in age-matched Wistar-Kyoto rats (7.36 +/- 0.32% versus 5.61 +/- 0.27%, p less than 0.05). However, compared with the normotensive controls, dopamine-induced increases in phospholipase C activity were significantly attenuated in the preparations of hypertensive rats in a concentration-dependent manner (13 +/- 6% versus 38 +/- 6% for 1 mM dopamine, p less than 0.05; 49 +/- 6% versus 71 +/- 9% for 3 mM dopamine, p less than 0.05; 50 +/- 16% versus 106 +/- 22%, p less than 0.05 for 10 mM dopamine).(ABSTRACT TRUNCATED AT 250 WORDS)