Vascular flow capacity of hindlimb skeletal muscles in spontaneously hypertensive rats

Total and regional skeletal muscle flows (radiolabeled microspheres) were determined in isolated maximally vasodilated hindquarters of spontaneously hypertensive rats (SHR) and age-matched (11-12 mo) normotensive Wistar-Kyoto rats (WKY) to assess the vascular flow capacity of the skeletal muscle vascular beds. Vascular flow capacity was estimated by measuring total hindquarters and regional muscle blood flows (under conditions of maximal vasodilation with papaverine or papaverine plus isoproterenol) over a wide range of perfusion pressures in WKY and SHR. Capillary exchange capacity was estimated by determining the capillary filtration coefficient. Isogravimetric capillary pressures and segmental vascular resistances were determined in each hindquarter. Isogravimetric flows and capillary pressures were not different between WKY and SHR. However, total and precapillary vascular resistances were significantly elevated in SHR, and postcapillary resistances were not different compared with WKY. Maximal capillary filtration coefficient values for the SHR group averaged 20% lower than WKY values, suggesting that hypertension was associated with a reduction in the microvascular surface area available for fluid exchange and, therefore, the capillary exchange capacity. Over the perfusion pressures studied, total hindquarters flows averaged 60% lower in SHR than in WKY. Flows to individual skeletal muscles averaged 76% lower in SHR than in WKY regardless of the muscle fiber type. Thus, modifications exist in the hindlimb skeletal muscle vasculature of SHR that reduces the capillary exchange capacity and limit the capacity of deliver flow at a given perfusion pressure gradient.     

Differential role of cyclooxygenase-1 and -2 on renal vasoconstriction to α1-adrenoceptor stimulation in normotensive and hypertensive rats

Aims

Hypertension is associated with the impairment of renal cyclooxygenase (COX) activity, which regulates vascular tone, salt and water balance and renin release. We aimed to evaluate the functional role of COX isoforms in kidneys isolated from spontaneously hypertensive rats (SHR) after α₁-adrenoceptor (α₁-AR) stimulation.

Main methods

Male six-month-old SHR and normotensive Wistar-Kyoto rats (WKY) were used. The kidneys were isolated to measure perfusion pressure and COX-1- or COX-2-derived prostanoids in response to α₁-AR activation.

Key findings

The basal perfusion pressure was higher in SHR kidneys compared with WKY kidneys (95 ± 11 vs. 68 ± 6 mm Hg, P < 0.05). Phenylephrine induced a greater vasopressor response in SHR kidneys (EC₅₀ of 1.89 ± 0.58 nmol) than WKY kidneys (EC₅₀ of 3.30 ± 0.54 nmol, P < 0.05 vs. SHR). COX-1 inhibition decreased the α₁-AR-induced vasoconstrictor response in WKY but did not affect SHR response, while COX-2 inhibition diminished the response in SHR. Both basal prostacyclin (PGI₂) and thromboxane A₂ (TxA₂) values were higher in SHR kidney perfusates (P < 0.05) and were reduced by COX-1 and COX-2 inhibitors in both strains. Furthermore, phenylephrine increased PGI₂ through COX-2 in WKY and through COX-1 in SHR, but the agonist did not significantly modify TxA₂ in both strains.

Significance

The data suggest that COX-1contributes to vasoconstrictor effects in WKY kidneys and that COX-2 has the same effect in SHR kidneys. The results also suggest that basal release of COX-2-derived vasoconstrictor prostanoids is involved in renal vascular hypersensitivity in SHR.     

A comparison of the cutaneous microvascular properties of the Spontaneously Hypertensive rat and the Wistar-Kyoto rat

The Spontaneously Hypertensive rat (SHR) and its non-hypertensive companion strain, the Wistar-Kyoto (WKY) rat, provide an excellent comparative model to permit study of the differential properties of cutaneous microvascular beds. We explored the possibility that chronically elevated vascular pressures in the SHR rat might affect the microvascular constitution of the skin. We measured skin blood flow at the back and at the paw of a group of 20-week-old WKY rats and a contrast group of SHR rats. We then performed skin biopsies at these two locations and used the NIH Image program to count and measure the size of capillaries, arterioles, and venules. We also determined microvascular density as percentage of total tissue area. At basal temperature, skin blood flow was similar in the two rat strains at both the back and paw. Heat induced vasodilatation resulted in a 50% increase in blood flow at the back, reaching the same level in the two rat groups. However, at the paw site, thermal stimulation resulted in significantly greater flow (39.3 +/- 3.1 ml/100 gm tissue per min) in the SHR rats than the WKY rats (28.6 +/- 1.9 ml/100 gm tissue per min, P < 0.05). The ratio of systemic arterial pressure to skin blood flow was computed as an index of vascular resistance to flow. At basal temperature, this index was 50% greater for the SHR rats at both skin sites. At 44 degrees C, the resistance index decreased at both sites in both rat groups but was still approximately 50% higher at the back of the SHR than the WKY rats. In contrast, the resistance index at 44 degrees C at the paw site fell to the same level in both the SHR and WKY rats. There were twice as many capillaries at the back of the WKY rats than at the back of the SHR rats (9.2 +/- 2.0 per mm2 vs. 4.7 +/- 1.2 per mm2, P < 0.05). Expressed as a percentage of total tissue area, the capillary density at the back in the WKY rats was 0.064 +/- 0.010% as compared to 0.034 +/- 0.008% in the SHR rats (P < 0.05). There were five times more arterioles at the paw compared to the back in both rat groups with no significant difference between the groups. We measured the diameter of the lumen and the thickness of the wall of each arteriole and computed their ratio as an index of possible media hypertrophy. There were minimal differences seen in these parameters between the two rat groups at the back and paw sites. The venular density was significantly higher at the paw than at the back in both rat groups with no significant difference between them. Reduced capillary density at the back of the SHR rats may be a developmental adaptation to high blood pressure. Such a reduction in the pathways of blood flow may help account for increased flow resistance at that site, independent of arteriolar vasoconstriction.     

Unique endothelin receptor binding in kidneys of ETB receptor deficient rats

The study investigated whether the amelioration of endothelial dysfunction by candesartan (2 mg.kg-1.day-1; 10 wk) in spontaneously hypertensive rats (SHR) was associated with modification of hepatic redox system. Systolic arterial pressure (SAP) was higher (P < 0.05) in SHR than in Wistar-Kyoto rats (WKY) and was reduced (P < 0.05) by candesartan in both strains. Acetylcholine (ACh) relaxations were smaller (P < 0.05) and contractions induced by ACh + NG-nitro-l-arginine methyl ester (l-NAME) were greater (P < 0.05) in SHR than in WKY. Treatment with candesartan enhanced (P < 0.05) ACh relaxations in SHR and reduced (P < 0.05) ACh + l-NAME contractions in both strains. Expression of aortic endothelial nitric oxide synthase (eNOS) mRNA was similar in WKY and SHR, and candesartan increased (P < 0.05) it in both strains. Aortic mRNA expression of the subunit p22phox of NAD(P)H oxidase was higher (P < 0.05) in SHR than in WKY. Treatment with candesartan reduced (P < 0.05) p22phox expression only in SHR. Malonyl dialdehyde (MDA) levels were higher (P < 0.05), and the ratio reduced/oxidized glutathione (GSH/GSSG) as well as glutathione peroxidase activity (GPx) were lower (P < 0.05) in liver homogenates from SHR than from WKY. Candesartan reduced (P < 0.05) MDA and increased (P < 0.05) GSH/GSSG ratio without affecting GPx. Vessel, lumen, and media areas were bigger (P < 0.05) in SHR than in WKY. Candesartan treatment reduced (P < 0.05) media area in SHR without affecting vessel or lumen area. The results suggest that hypertension is not only associated with elevation of vascular superoxide anions but with alterations of the hepatic redox system, where ANG II is clearly involved. The results further support the key role of ANG II via AT1 receptors for the functional and structural vascular alterations produced by hypertension.     

Acute intravenous calcitonin: Failure to modify systemic blood pressure

Calcium and a principal calcuim-regulating hormone, PTH, have been characterized as possessing vasoactive properties in the spontaneously hypertensive rat (SHR). Calcitonin is another calcium-regulating peptide with primary, but opposing effects on many of the same target organs, and capable of modifying both extracellular and intracellular calcium distribution. We sought to determine whether calcitonin, like PTH, exhibits vasoactivity in the SHR and its control, the Wistar-Kyoto rat (WKY). Three male SHR and 3 male normotensive WKY received intravenous injections (range 1–100 μg/kg) of synthetic human calcitonin. Seven SHR and 7 WKY received equivalent doses of the more potent peptide, synthetic salmon calcitonin. Intraarterial pressure was monitored continuously. Neither analog of calcitonin produced significant changes in blood pressure. Serum ionized calcium levels 30 minutes postinjection were unchanged from baseline in the WKY; in the SHR, postinjection serum ionized calcium levels were significantly lower than baseline values (pre=1.12±0.01 mmol/l vs. post 1.08±0.01 mmol/l, p<0.05). We conclude that calcitonin modifies extracellular calcium, but does not have demonstrable, acute systemic cardiovascular effects.     

Insulin resistance in spontaneously hypertensive rats is associated with endothelial dysfunction characterized by imbalance between NO and ET-1 production

Insulin stimulates production of NO in vascular endothelium via activation of phosphatidylinositol (PI) 3-kinase, Akt, and endothelial NO synthase. We hypothesized that insulin resistance may cause imbalance between endothelial vasodilators and vasoconstrictors (e.g., NO and ET-1), leading to hypertension. Twelve-week-old male spontaneously hypertensive rats (SHR) were hypertensive and insulin resistant compared with control Wistar-Kyoto (WKY) rats (systolic blood pressure 202 +/- 11 vs. 132 +/- 10 mmHg; fasting plasma insulin 5 +/- 1 vs. 0.9 +/- 0.1 ng/ml; P < 0.001). In WKY rats, insulin stimulated dose-dependent relaxation of mesenteric arteries precontracted with norepinephrine (NE) ex vivo. This depended on intact endothelium and was blocked by genistein, wortmannin, or N(omega)-nitro-l-arginine methyl ester (inhibitors of tyrosine kinase, PI3-kinase, and NO synthases, respectively). Vasodilation in response to insulin (but not ACh) was impaired by 20% in SHR (vs. WKY, P < 0.005). Preincubation of arteries with insulin significantly reduced the contractile effect of NE by 20% in WKY but not SHR rats. In SHR, the effect of insulin to reduce NE-mediated vasoconstriction became evident when insulin pretreatment was accompanied by ET-1 receptor blockade (BQ-123, BQ-788). Similar results were observed during treatment with the MEK inhibitor PD-98059. In addition, insulin-stimulated secretion of ET-1 from primary endothelial cells was significantly reduced by pretreatment of cells with PD-98059 (but not wortmannin). We conclude that insulin resistance in SHR is accompanied by endothelial dysfunction in mesenteric vessels with impaired PI3-kinase-dependent NO production and enhanced MAPK-dependent ET-1 secretion. These results may reflect pathophysiology in other vascular beds that directly contribute to elevated peripheral vascular resistance and hypertension.     

NAD(P)H oxidase-derived peroxide mediates elevated basal and impaired flow-induced NO production in SHR mesenteric arteries in vivo

Nitric oxide (NO) and reactive oxygen species (ROS) have fundamentally important roles in the regulation of vascular tone and remodeling. Although arterial disease and endothelial dysfunction alter NO and ROS levels to impact vasodilation and vascular structure, direct measurements of these reactive species under in vivo conditions with flow alterations are unavailable. In this study, in vivo measurements of NO and H2O2 were made on mesenteric arteries to determine whether antioxidant therapies could restore normal NO production in spontaneously hypertensive rats (SHR). Flow was altered from approximately 50-200% of control in anesthetized Wistar-Kyoto rats (WKY) and SHR by selective placement of microvascular clamps on adjacent arteries while NO and H2O2 were directly measured with microelectrodes. Relative to WKY, SHR had significantly increased baseline NO and H2O2 concentrations (2,572 +/- 241 vs. 1,059 +/- 160 nM, P < 0.01; and 26 +/- 7 vs. 7 +/- 1 microM, P < 0.05, respectively). With flow elevation, H2O2 but not NO increased in SHR; NO but not H2O2 was elevated in WKY. Apocynin and polyethylene-glycolated catalase decreased baseline SHR NO and H2O2 to WKY levels and restored flow-mediated NO production. Suppression of NAD(P)H oxidase with gp91ds-tat decreased SHR H2O2 to WKY levels. Addition of topical H2O2 to increase peroxide to the basal concentration measured in SHR elevated WKY NO to levels observed in SHR. The results support the hypothesis that increased vascular peroxide in SHR is primarily derived from NAD(P)H oxidase and increases NO concentration to levels that cannot be further elevated with increased flow. Short-term and even acute administration of antioxidants are able to restore normal flow-mediated NO signaling in young SHR.     

Arterial hypertension exacerbates oxidative stress in early diabetic retinopathy

The present study was undertaken to investigate the redox status in the retina of an experimental model that combines hypertension and diabetes. Spontaneously hypertensive rats (SHR) and their control Wystar Kyoto (WKY) rats were rendered diabetic and, after 20 days, the rats were sacrificed and the retinas collected. The superoxide production was higher in diabetic than in control WKY (p<0.03) and SHR rats showed elevated superoxide production compared with WKY groups (p<0.009). The glutathione antioxidant system was diminished only in diabetic SHR (p<0.04). Tirosyne nitration was higher in diabetic WKY and control SHR compared with control WKY (p<0.03), and further increment was observed in diabetic SHR (p<0.02). The DNA damage estimated by immunohystochemistry for 8-OHdG was higher in control SHR than in WKY, mainly in diabetic SHR (p<0.0001). Hypertension aggravates oxidative-induced cytotoxicity in diabetic retina due to increasing of superoxide production and impairment of antioxidative system.     

Effects of high-sucrose feeding on insulin resistance and hemodynamic responses to insulin in spontaneously hypertensive rats

This study was designed to investigate the effects of a sucrose diet on vascular and metabolic actions of insulin in spontaneously hypertensive rats (SHR). Male SHR were randomized to receive a sucrose or regular chow diet for 4 wk. Age-matched, chow-fed Wistar-Kyoto (WKY) rats were used as normotensive control. In a first series of experiments, the three groups of rats had pulsed Doppler flow probes and intravascular catheters implanted to determine blood pressure, heart rate, and blood flows. Insulin sensitivity was assessed during a euglycemic hyperinsulinemic clamp performed in conscious rats. In a second series of experiments, new groups of rats were used to examine glucose transport activity in isolated muscles and to determine endothelial nitric oxide synthase (eNOS) protein expression in muscles and endothelin content in vascular tissues. Sucrose feeding was shown to markedly enhance the pressor response to insulin and its hindquarter vasoconstrictor effect when compared with chow-fed SHR. A reduction in eNOS protein content in muscle, but no change in vascular endothelin-1 protein, was noted in sucrose-fed SHR when compared with WKY rats, but these changes were not different from those noted in chow-fed SHR. Similar reductions in insulin-stimulated glucose transport were observed in soleus muscles from both groups of SHR when compared with WKY rats. In extensor digitorum longus muscles, a significant reduction in insulin-stimulated glucose transport was only seen in sucrose-fed rats when compared with the other two groups. Environmental factors, that is, high intake of simple sugars, could possibly potentiate the genetic predisposition in SHR to endothelial dysfunction and insulin resistance.     

Multinuclear NMR studies of intracellular cations in the prehypertensive rat kidney

We previously reported a significant derangement of intracellular free calcium ion concentration in the isolated perfused kidney of adult spontaneously hypertensive rat (SHR) (J. Biol. Chem. 267, 3637–3643, 1992). In order to investigate whether an abnormality in intracellular free calcium or another ion precedes the development of elevated blood pressure in SHR, we have now compared intracellular free Ca²⁺, Na⁺ and pH, using ³¹P, ¹⁹F, and triple quantum-filtered (TQ) ²³Na NMR, in perfused kidneys from prehypertensive young SHR and normotensive young Wistar-Kyoto (WKY) rats (5–6 weeks old) which showed no significant difference in blood pressure B.P.=120±5 mmHg and 115±3 mmHg, for SHR and WKY rats, respectively). Like the adult kidney, no significant differences in intracellular ATP concentration or intracellular pH were found between young prehypertensive SHR and normotensive WKY rat kidneys. The TQ ²³Na NMR signal was 47% higher in the SHR kidney, but, due to biological variability and measurement errors, this difference could not be shown to be statistically significant. However, a significant (40%; P<0.05) increase was found in O₂ consumption rate, a measure of the Na⁺/K⁺-ATPase activity, of the young prehypertensive SHR kidney in comparison to the age-matched WKY rat kidney (7.25±0.75 for SHR vs. 5.17±0.18 μmola O₂/min g for WKY rat, n = 6). Furthermore, a highly significant (92%; P<0.02) increase in intracellular free Ca²⁺ concentration was observed in kidneys from young SHR that had noy yet been developed high blood pressure in comparison to the kidneys from young normotensive WKY rats (648±76 nM vs. 339±39 nM, n = 4, despite the fact that there was no significant difference in blood pressure. Increased intracellular free Ca²⁺ thus appears to be part of a primary defect, in the prehypertesive young SHR kidney, which may, by way of increased release of arachidonic acid, and subsequent increased production of vasoconstricting arachidonic acid metabolites via the cytochrome P450 pathway, induce elevated blood pressure in the adult SHR.     

Vascular smooth muscle cell growth and insulin regulation of mitogen-activated protein kinase in hypertension

Hyperinsulinemia (HI) and insulin resistance (IR) are frequentlyassociated with hypertension and atherosclerosis. However, the exactroles of HI and IR in the development of hypertension are unclear.Mitogen-activated protein kinases (MAPK) are well-characterized intracellular mediators of cell proliferation. In this study, weexamined the contribution of MAPK pathway in insulin-stimulated mitogenesis using primary vascular smooth muscle cells (VSMCs) isolatedfrom aortas of normotensive Wistar-Kyoto rats (WKY) and spontaneoushypertensive rats (SHR). VSMCs were grown to confluence in culture,serum starved, and examined for DNA synthesis {using [³H]thymidine (TDR),immunoprecipitated MAPK activity, and MAPK phosphatase (MKP-1)induction}. Basal rate of TDR incorporation into DNA was twofoldhigher in SHR compared with WKY (P < 0.005). Insulin caused a dose-dependent increase in TDR incorporation (150% over basal levels with 100 nM in 12 h). Stimulation was sustained for 24 h with a decline toward basal in 36 h. Pretreatment with insulin-like growth factor I (IGF-I) receptor antibody did notabolish mitogenesis mediated by 10-100 nM insulin, suggesting thatinsulin effect is mediated via its own receptors. Insulin had a smallmitogenic effect in WKY (33% over basal). Insulin-stimulated mitogenesis was accompanied by a dose-dependent increase in MAPK activity in SHR, with a peak activation (>2-fold over basal) between 5 and 10 min with 100 nM insulin. Insulin had very small effects onMAPK activity in WKY. In contrast, serum-stimulated MAPK activation wascomparable in WKY and SHR. Pretreatment with MEK inhibitor, PD-98059,completely blocked insulin's effect on MAPK activation andmitogenesis. Inhibition of phosphatidylinositol 3-kinase with wortmannin also prevented insulin's effects on MAPK activation andmitogenesis. In WKY, insulin and IGF-I treatment resulted in a rapidinduction of MKP-1, the dual-specificity MAPK phosphatase. Incontrast, VSMCs from SHR were resistant to insulin with respect toMPK-1 expression. We conclude that insulin is mitogenic in SHR, and theeffect appears to be mediated by sustained MAPK activation due toimpaired insulin-mediated MKP-1 mRNA expression, which may act asan inhibitory feedback loop in attenuating MAPK signaling.

     

Impaired UTP-induced relaxation in the carotid arteries of spontaneously hypertensive rats

Uridine 5′-triphosphate (UTP) has an important role as an extracellular signaling molecule that regulates inflammation, angiogenesis, and vascular tone. While chronic hypertension has been shown to promote alterations in arterial vascular tone regulation, carotid artery responses to UTP under hypertensive conditions have remained unclear. The present study investigated carotid artery responses to UTP in spontaneously hypertensive rats (SHR) and control Wistar Kyoto rats (WKY). Accordingly, our results found that although UTP promotes concentration-dependent relaxation in isolated carotid artery segments from both SHR and WKY after pretreatment with phenylephrine, SHR exhibited significantly lower arterial relaxation responses compared with WKY. Moreover, UTP-induced relaxation was substantially reduced by endothelial denudation and by the nitric oxide (NO) synthase inhibitor N^G-nitro-L-arginine in both SHR and WKY. The difference in UTP-induced relaxation between both groups was abolished by the selective P2Y₂ receptor antagonist AR-C118925XX and the cyclooxygenase (COX) inhibitor indomethacin but not by the thromboxane-prostanoid receptor antagonist SQ29548. Furthermore, we detected the release of PGE₂, PGF_2α, and PGI₂ in the carotid arteries of SHR and WKY, both at baseline and in response to UTP. UTP administration also increased TXA₂ levels in WKY but not SHR. Overall, our results suggest that UTP-induced relaxation in carotid arteries is impaired in SHR perhaps due to impaired P2Y₂ receptor signaling, reductions in endothelial NO, and increases in the levels of COX-derived vasoconstrictor prostanoids.

     

Diminished brain synaptic plasma membrane ca2+-atpase activity in spontaneously hypertensive rats: Association with reduced anesthetic requirements

We have recently reported that plasma membrane Ca²⁺-ATPase ( PMCA) pumping activity in rat brain synaptic plasma membranes (SPM) was reduced by in vitro or prior in vivo exposure to inhalation anesthetics (IA). In addition, rats with streptozocin-induced diabetes were found to have diminished brain synaptic PMCA pumping and a decrease in the partial pressures of several IA required to prevent movement in response to stimulation, defined as the minimum effective dose or MED. Diminished PMCA activity in erythrocytes of spontaneously hypertensive rats (SHR) has been noted. Because PMCA is ubiquitous, it seemed possible that PMCA pumping might be decreased in the brain of SHR and perhaps associated with decreased IA requirement. Eighteen SHR and 18 control, normotensive Wistar-Kyoto rats (WKY) were studied. PMCA activity was assessed by measurement of Ca²⁺ uptake into synaptic plasma membrane vesicles prepared from cerebrum and diencephalon-mesencephalon (D-M) in WKY and SHR. Ca²⁺ pumping was significantly less in SHR than in WKY, 85% of control in the cerebrum and 90% in the D-M (p < 0.01). The MEDs for halothane, isoflurane and desflurane were also lower in SHR than in WKY, 91%, 90% and 89%, respectively, of control (p < 0.05). Thus, an animal model of primary hypertension (SHR) manifested diminished brain synaptic PMCA activity and reduced MED for several volatile anesthetics. These findings provide further evidence for a role for PMCA in anesthetic action.     

Urinary levels of 2,3-dinor-6-oxo-PGF1α: A reliable index of the prodcution of PGI2 in the spontaneously hypertensive rat

The urinary levels of 2,3-dinor-6-oxo-PGF_1α (PGI₂-M), a major metabolite of PGI₂, are determined by the balance between the amount of PGI₂ synthesized and the extent of its further metabolic oxidation. The purpose of the present study was to determine if the urinary excretion of PGI₂-M can be used as a reliable index of the $\text{in vivo}$ production of PGI₂ in both normal Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). This involved the exclusion of differences in metabolism between these two strains of rats. In order to do so, we monitored the urinary excretion of PGI₂-M during paired intravenous infusions of 6-oxo-PGF_1α (the stable product of the spontaneous hydrolysis of PGI₂) in conscious, unrestrained SHR and WKY rats aged 12–15 weeks, in doses ranging from 250 to 700 ng. In one experiment, PGI₂ was infused instead of 6-oxo-PGF_1α.The results of these experiments indicate that SHR and WKY rats are equal with regard to the transformation of 6-oxo-PGF_1α and PGI₂ into PGI₂-M. For both groups, there is a good correlation between the amount of 6-oxo-PGF_1α infused and the amount of PGI₂-M excreted in urine. These observations confirm the validity of using the urinary levels of 2,3-dinor-6-oxo-PGF_1α as an index of PGI₂ production in both WKY and SHR. In addition, they support the conclusions drawn from our previous studies, namely that SHR do not produce more PGI₂ than WKY rats $\text{in vivo}$, contrary to the situation prevailing $\text{in vitro}$.     

Exercise training improves systolic function in hypertensive myocardium

The general purpose of this study was to test the effect of exercise training on the left ventricular (LV) pressure-volume relationship (LV/PV) and apoptotic signaling markers in normotensive and hypertensive hearts. Four-month-old female normotensive Wistar-Kyoto rats (WKY; n = 37) and spontaneously hypertensive rats (SHR; n = 38) were assigned to a sedentary (WKY-SED, n = 21; SHR-SED, n = 19) or treadmill-trained (WKY-TRD, n = 16; SHR-TRD, n = 19) group (～60% Vo(2 peak), 60 min/day, 5 days/wk, 12 wk). Ex vivo LV/PV were established in isovolumic Langendorff-perfused hearts, and LV levels of Akt, phosphorylated Akt (Akt(Pi)), Bad, phosphorylated Bad (Bad(Pi)) c-IAP, x-IAP, calcineurin, and caspases 3, 8, and 9 were measured. Heart-to-body weight ratio was increased in SHR vs. WKY (P < 0.05), concomitant with increased calcineurin mRNA (P < 0.05). There was a rightward shift in the LV/PV (P < 0.05) and a reduction in systolic elastance (E(s)) in SHR vs. WKY. Exercise training corrected E(s) in SHR (P < 0.05) but had no effect on the LV/PV in WKY. Caspase 3 was increased in SHR-SED relative to WKY-SED, while Bad(Pi,) c-IAP, and x-IAP were significantly lower in SHR relative to WKY (P < 0.05). Exercise training increased Bad(Pi) in both WKY and SHR but did not alter caspase 9 activity in either group. While caspase 3 activity was increased with training in WKY (P < 0.05), it was unchanged with training in SHR. We conclude that moderate levels of regular aerobic exercise attenuate systolic dysfunction early in the compensatory phase of hypertrophy, and that a differential phenotypical response to moderate-intensity exercise exists between WKY and SHR.     

Reduced fetal, placental, and amniotic fluid PTHrP in the growth-restricted spontaneously hypertensive rat

Evidence implicates pivotal roles for parathyroid hormone-related protein (PTHrP) in stimulating cell growth and differentiation, placental calcium transport, and placental vasodilatation. As spontaneously hypertensive rat (SHR) fetuses are growth restricted compared with those of its normotensive control, the Wistar Kyoto (WKY) rat, we examined intrauterine PTHrP and total and ionic calcium concentrations in these rats. Fetal plasma PTHrP concentrations, but not total calcium concentrations, were lower in the SHR compared with WKY (P < 0.05). SHR placental concentrations of PTHrP were lower than in WKY (P < 0.03) and failed to show the increase observed in WKY near term (P < 0.05). PTHrP concentrations in amniotic fluid from SHR were not raised near term and were lower compared with WKY (P < 0.0005). The increased ionic calcium concentrations in amniotic fluid in the WKY near term (P < 0.05) were not detected in the SHR. Thus SHR fetal plasma, placental, and amniotic fluid PTHrP concentrations were reduced and associated with fetal growth restriction. We suggest that PTHrP may play a role in the etiology of both growth restriction during pregnancy and hypertension later in life.     

Heterogeneity in Arterial Remodeling among Sublines of Spontaneously Hypertensive Rats

Objectives

Spontaneously hypertensive rats (SHR) have been used frequently as a model for human essential hypertension. However, both the SHR and its normotensive control, the Wistar Kyoto rat (WKY), consist of genetically different sublines. We tested the hypothesis that the pathophysiology of vascular remodeling in hypertension differs among rat sublines.

Methods and Results

We studied mesenteric resistance arteries of WKY and SHR from three different sources, at 6 weeks and 5 months of age. Sublines of WKY and SHR showed differences in blood pressure, body weight, vascular remodeling, endothelial function, and vessel ultrastructure. Common features in small mesenteric arteries from SHR were an increase in wall thickness, wall-to-lumen ratio, and internal elastic lamina thickness.

Conclusions

Endothelial dysfunction, vascular stiffening, and inward remodeling of small mesenteric arteries are not common features of hypertension, but are subline-dependent. Differences in genetic background associate with different types of vascular remodeling in hypertensive rats.     

The influence of adrenal vein occlusion on whole-kidney hemodynamics in the spontaneously hypertensive rats.

It has been shown that occlusion of the adrenal vein causes an increase in renal vascular resistance in the ipsilateral kidney in Wistar Kyoto rats (WKY). The most probable mechanism of this phenomenon is the direct inflow of adrenal catecholamines to the kidney by the adrenal renal portal circulation (ARPC). As the number of vessels of the ARPC is bigger and the tonic sympathetic activity is higher in spontaneously hypertensive rats (SHR), the aim of the current study was to compare the effect of adrenal vein occlusion on renal vascular resistance between SHR and WKY. Mean arterial blood pressure and renal blood flow (RBF) were measured and renal vascular resistance (RVR) was calculated before and after closure of the adrenal vein. Occlusion of the adrenal vein significantly reduced RBF and increased RVR in both strains of rats. The rise of the RVR was significantly higher in SHR than in WKY. Therefore we assume that the hemodynamic responsiveness of the kidney due to increase in blood flow through ARPC is greater in SHR and may contribute to the development of arterial hypertension in this strain of rat.     

Differential regulation of transient receptor potential melastatin 6 and 7 cation channels by ANG II in vascular smooth muscle cells from spontaneously hypertensive rats

Intracellular Mg2+ depletion has been implicated in vascular dysfunction in hypertension. We demonstrated that transient receptor potential melastatin 7 (TRPM7) cation channels mediate Mg2+ influx in VSMCs. Whether this plays a role in [Mg2+]i deficiency in hypertension is unclear. Here, we tested the hypothesis that downregulation of TRPM7 and its homologue TRPM6 is associated with reduced [Mg2+]i and that ANG II negatively regulates TRPM6/7 in vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR). Cultured VSMCs from Wistar Kyoto (WKY) and SHR were studied. mRNA and protein expression of TRPM6 and TRPM7 were assessed by RT-PCR and immunoblotting, respectively. Translocation of annexin-1, specific TRPM7 substrate, was measured as an index of TRPM7 activation. [Mg2+]i was determined using mag fura-2. VSMCs from WKY and SHR express TRPM6 and TRPM7. Basal TRPM6 expression was similar in WKY and SHR, but basal TRPM7 content was lower in VSMCs from SHR vs. WKY. This was associated with significantly reduced [Mg2+]i in SHR cells (P < 0.01). ANG II time-dependently increased TRPM6 expression, with similar responses in WKY and SHR. ANG II significantly increased TRPM7 expression in WKY (P < 0.05), but not in SHR. Annexin-1 translocation was reduced 1.5-2-fold in SHR vs. WKY. Our findings demonstrate that TRPM6 and TRPM7 are differentially regulated in VSMCs from SHR and WKY. Whereas TRPM6 is unaltered in SHR, expression of TRPM7 is blunted. This was associated with attenuated annexin-1 translocation and decreased VSMC [Mg2+]i in SHR. Downregulation of TRPM7, but not TRPM6, may play a role in altered Mg2+ homeostasis in VSMCs from SHR.     

The effect of cholecystokinin octapeptide on pituitary-adrenal hormone secretion

The purpose of this investigation was to determine the influence of cholecystokinin octapeptide (CCK-OP) on pituitary-adrenal hormone secretion. CCK-OP at a dose of 5 μg/kg (i.p.) elevated plasma corticosterone from 27 to 43 μg/100 ml in one experiment and from 12 to 50 μg/100 ml in a second experiment: Lower doses of CCK-OP (0.5 μg/kg) elevated corticosterone from 12 μg/100 ml to 20 μg/100 ml. CCK-OP (1, 10, and 100 ng/ml) had no effect on ACTH-induced corticosterone released by isolated adrenal cells in vitro when tested in the presence of 50 pg of ACTH_1?24. 100 and 500 ng of CCK-OP resulted in an increased pituitary ACTH release equal to 123% (n.s.) and a 206% (P < 0.05) of control, respectively. In comparison, a $\text{3}\text{5}$ hypothalamic stalk median eminence equivalent increased ACTH release to 313% of control (P < 0.05). The exact mechanism of this CCK effect on pituitary ACTH release is unknown. Although it is likely that the direct effects on the pituitary in vitro represent a pharmacologic and not a physiologic effect of this peptide, in vivo doses are between doses used for pancreatic effects and satiety effects suggesting that there may be a physiologic stimulating action of this peptide on the hypothalamic-pituitary-adrenal axis but at a level above the adrenal and pituitary.