Differential expression of melatonin receptors in spontaneously hypertensive rats.

Quantitative autoradiography was used to compare melatonin receptors in brain areas and arteries of young (4 weeks old) and adult (14 weeks old) spontaneously hypertensive rats (SHR) to those in age-matched normotensive controls, Wistar-Kyoto (WKY) rats. Age and strain influenced the number of melatonin receptors in an anatomically selective manner, and the most striking changes occurred in arterial receptors. Melatonin receptors were not detectable in the anterior cerebral arteries of adult SHR. In the caudal artery, melatonin receptors decreased with age in both strains, but the decrease was more pronounced in SHR. When compared to age-matched WKY rats, the number of caudal artery receptors was higher in young and lower in adult SHR. The number of melatonin receptors was higher in the area postrema of adult SHR when compared to adult WKY rats, but in the suprachiasmatic nucleus, no such differences between the two strains were present. Alterations in receptor density were not accompanied by changes in binding affinity. Our results indicate that in the rat melatonin receptors show different developmental patterns according to location and that the receptors may be expressed differentially in genetic hypertension.     

Diminished expression of constitutive nitric oxide synthases in the kidney of spontaneously hypertensive rat

In kidney, nitric oxide (NO) synthesized by nitric oxide synthase (NOS) regulates sodium and water excretion, and renal medullary blood flow. The expression of constitutive NOS, endothelial NOS (eNOS) and neuronal NOS (nNOS), were assessed in kidney of the spontaneously hypertensive rat (SHR) and the normotensive Wistar Kyoto (WKY) rat by Western blot analysis and immunocytochemistry. Neuronal NOS expression was observed in the cortex and eNOS was detected only in theinner medulla of both WKY and SHR. In SHR, expression of eNOS was attenuated to 35.1 +/- 10.8%, while expression of nNOS was only 57.5 +/- 5.7% of the levels seen in WKY rat. Immunocytochemical studies revealed decreased staining of nNOS in the macula densa, collecting ducts and in the glomerulus of SHR compared to WKY rat. Endothelial NOS immunoreactivity was restricted to vascular structures of the inner intima cells and smooth muscle cells, and was markedly reduced in the vasculature of SHR. The decreased renal blood flow observed in SHR may be linked to a diminished expression of eNOS and nNOS, underscoring the importance of these enzymes in the pathophysiology and maintenance of genetic hypertension.     

Myocardial beta-adrenergic receptors in the stroke-prone spontaneously hypertensive rat

In view of the severity of the hypertension in the stroke-prone spontaneously hypertensive rats (sp-SHR), myocardial beta-adrenergic receptors were investigated by the binding of (?)[³H]-dihydroalprenolol (DHA) to membranes from sp-SHR (9-week-old males, Okamoto-Aoki strain) and age-matched and sex-matched normotensive Wistar-Kyoto rats. Scatchard analysis showed no significant differences in binding parameters between sp-SHR and normal rats. Myocardial membranes from sp-SHR bound 31.8 ± 2.3 fmol DNA per mg protein with a dissociation constant of 3.8 ± 0.9 nm, whereas membranes from normal rats bound 33.4 ± 2.9 fmol DHA per mg protein with a dissociation constant of 3.9 ± 1.0 nm. However, mean arterial pressure and heart rate determined directly via aortic cannulae, while the rats were conscious and unrestrained, were significantly higher in sp-SHR. Plasma norepinephrine concentration was also significantly higher in sp-SHR. The finding that cardiac beta-adrenergic receptors are unchanged, despite evidence of increased sympathetic nerve activity, suggests that in the sp-SHR there may be a failure of catecholamine-induced “down regulation” of beta-adrenergic receptors. This defect could contribute to the increased cardiac drive in these animals and may thus explain the severity of the hypertension in this strain of spontaneously hypertensive rats.     

Activation of dopamine D2-like receptors attenuates pulmonary C-fiber hypersensitivity in rats

This study was performed to determine whether activation of dopamine D2-like receptors inhibits the hyperresponsiveness of pulmonary C fibers induced by inflammatory mediators such as prostaglandin E2 (PGE2). In anesthetized, open-chest rats, constant infusion of PGE2 (1.5-4.5 microg/kg per minute, 2 minutes) significantly enhanced the C-fiber response to capsaicin injection. At 20 minutes after pretreatment with quinpirole (3 mg/kg, intravenous), a D2-like receptor agonist, the hyperresponsiveness to capsaicin of the same C fibers induced by PGE2 infusion was markedly attenuated, and this inhibitory effect lasted for more than 90 minutes. The effect of quinpirole was dose dependent and was antagonized by pretreatment with domperidone (5 mg/kg, intravenous), a D2-like receptor antagonist, administrated 10 minutes before the quinpirole injection. In a separate series of experiments, C-fiber responses to injections of phenyl biguanide and lactic acid and to constant-pressure lung inflation were augmented by PGE2; these potentiating responses were also significantly reduced by quinpirole. Furthermore, the effect of quinpirole was equally effective in inhibiting the increase in excitability of pulmonary C fibers induced by alveolar hypercapnia or constant infusion of adenosine. In conclusion, these results clearly show that activation of the dopamine D2-like receptors attenuates the hyperresponsiveness of pulmonary C fibers to both chemical stimuli and lung inflation.     

自发性高血压大鼠心血管组织中肾上腺髓质素2受体系统的变化

目的:探讨自发性高血压大鼠(SHR)心血管组织中肾上腺髓质素2(ADM2)及其受体系统的基因表达和蛋白水平变化,以及与ADM2血浆水平的相互关系.方法:8只11周龄的雄性SHR(SHR组),8只同龄的雄性Wistar Kyoto大鼠(WKY组).半定量RT-PCR方法测定大鼠心血管组织中ADM2及其受体系统降钙素受体样受体(CRLR)和受体活性修饰蛋白(RAMPs)mRNA水平;Western blot法测定心血管组织中CRLR和RAMPs的蛋白含量;放射免疫法测定血浆中ADM2含量.结果:①SHR心肌中ADM2、CRLR、RAMP1、RAMP2和RAMP3的mRNA水平较WKY组分别高76.1%、41.6%、69.2%、48.3%和109.1%(均P＜0.05);主动脉中分别高171.11%(P＜0.01)、69.9%(P＜0.05)、100.09%(P＜0.01)、131.8 0%和69.7%(均P＜0.05).②SHR心肌中CRLR、RAMP1和RAMP3的蛋白水平较WKY组分别高136.0%、60.3%、63.9%(均P＜0.05),而RAMP2则显著增高292.5%(P＜0.01);SHR主动脉中CRLR、RAMP1、RAMP2和RAMP3的蛋白水平较WKY组分别高112.4%、92.3%、41.1%和67.7%(均P＜0.01).③SHR的ADM2血浆含量和受体的蛋白水平-CRLR、RAMP1、RAMP2在主动脉中的含量呈显著正相关(r=0.883 8,0.929 9,0.888 1,均P＜0.05).结论:ADM2及其受体系统在原发性高血压的发生发展过程中可能具有重要的病理生理意义.     

Paradoxical structural effects in the unilaterally denervated spontaneously hypertensive rat kidney

OBJECTIVE: To determine the effects of chronic denervation on renal vascular structure and function in young adult spontaneously hypertensive rats (SHRs). DESIGN: Unilateral renal denervation (SHRUDx) or sham-operation (SHRS) was performed in SHRs at 6 weeks of age. At 10 weeks, rats were allocated to one of three procedures designed to examine renal vascular structure and function. A further group underwent bilateral renal denervation. METHODS: In SHRUDx or SHRS groups, either the kidneys were perfusion-fixed for stereological estimates of artery wall and lumen dimensions or for vascular casting to determine arteriole lumen diameters, or the rats were anaesthetized for estimation of glomerular capillary pressure. RESULTS: Chronic unilateral renal denervation had no significant effect on the development of hypertension between 6 and 10 weeks of age, as previously reported, but resulted in luminal narrowing of the interlobular artery (denervated group 52 +/- 2 mum, sham-operated group 64 +/- 1 mum; P < 0.01 for interaction between strain and treatment), without alterations in interlobular or arcuate artery wall dimensions. There were no significant effects on either afferent or efferent arteriole lumen diameters. Estimated glomerular capillary pressure was significantly lower in the denervated kidneys of SHRUDx (47 +/- 1 mmHg) compared with kidneys of the SHRS (50 +/- 1 mmHg; P < 0.04). Mean arterial pressure was approximately 12 mmHg lower in the bilaterally denervated SHRs than in the sham-operated SHRs. CONCLUSIONS: Although bilateral denervation attenuated the development of hypertension in SHRs, unilateral denervation did not, indicating that one neurally intact kidney was sufficient to drive the normal development of SHR hypertension, but only with apparent prohypertensive compensatory changes in the denervated kidney.     

Overexpression of inducible nitric oxide synthase in the kidney of the spontaneously hypertensive rat

In kidney, nitric oxide (NO) produced by nitric oxide synthase (NOS) regulates sodium and water excretion and renal medullary blood flow. However, excessive NO production causes nitrative damage and oxidative stress. Since oxidative stress may be linked to hypertension, we examined the expression and activity of inducible NOS (iNOS) in the kidney of the spontaneously hypertensive rat (SHR) and compared our findings to control normtotensive Wistar Kyoto (WKY) rat. Compared with WKY rat, there was significant (p < .05) overexpression (by 96%) and increased (2-fold) activity of iNOS in the cortex but not in the outer medulla, of SHR kidney; in the inner medulla, there was a 6.9-fold increase in iNOS activity in SHR. Increased expression (by 104%) and activity (3.3-fold) of iNOS was specifically observed in proximal tubules (PTs) of the cortex, accompanied by higher (2-fold) tissue nitrite levels. Although certain antioxidant enzymes such as catalase and Mn-superoxide dismutase were overexpressed, glutathione peroxidase was underexpressed in SHR PTs. Overexpression of the inducer of the iNOS promoter, nuclear factor-kappaB (NF-kappaB), with elevated nitrotyrosinylated proteins, further confirmed an elevated state of iNOS-induced oxidative stress in SHR kidneys, possibly signifying its role in the maintenance of essential hypertension seen in these animals.     

Perturbation of D1 dopamine and AT1 receptor interaction in spontaneously hypertensive rats

The dopaminergic and renin-angiotensin systems interact to regulate blood pressure. Because this interaction may be perturbed in genetic hypertension, we studied D1 dopamine and AT1 angiotensin receptors in immortalized renal proximal tubule (RPT) and A10 aortic vascular smooth muscle cells. In normotensive Wistar-Kyoto (WKY) rats, the D1-like agonist fenoldopam increased D1 receptors but decreased AT1 receptors. These effects were blocked by the D1-like antagonist SCH 23390 (10(-7) mol/L per 24 hours). In spontaneously hypertensive rat (SHR) RPT cells, fenoldopam also decreased AT1 receptors but no longer stimulated D1 receptor expression. Basal levels of AT1/D1 receptor coimmunoprecipitation were greater in WKY RPT cells (29+/-2 density units, DU) than in SHR RPT cells (21+/-2 DU, n=7 per group, P<0.05). The coimmunoprecipitation of D1 and AT1 receptors was increased by fenoldopam (10(-7) mol/L per 24 hours) in WKY RPT cells but decreased in SHR RPT cells. The effects of fenoldopam in RPT cells from WKY rats were similar in aortic vascular smooth muscle cells from normotensive BD IX rats, that is, fenoldopam decreased AT1 receptors and increased D1 receptors. Our studies show differential regulation of the expression of D1 and AT1 receptors in RPT cells from WKY and SHR. This regulation and D1/AT1 receptor interaction are different in RPT cells of WKY and SHR. An altered interaction of D1 and AT1 receptors may play a role in the impaired sodium excretion and enhanced vasoconstriction in hypertension.     

Decreased expression of Na+-H+ exchanger isoforms 1 and 3 in denervated spontaneously hypertensive rat kidney

To determine whether the sympathetic nerve plays a role in the regulation of Na⁺-H⁺ exchange (NHE) in the kidney of spontaneously hypertensive rats (SHR), we investigated the expression of NHE and NHE regulatory protein family (NHERF) in the denervated kidneys compared with intact kidneys. Twelve-week-old male SHR and age-matched Wistar Kyoto (WKY) rats were used. SHR were randomly assigned to the renal denervated (RDNX, n = 8) or Sham (n = 8) groups. The protein and mRNA expression of NHE1, NHE3, NHERF1 and NHERF2 were assessed in the kidney of the groups. Following the renal denervation, immunohistochemistry and western blot analysis showed that NHE1 and NHE3 protein were signi?cantly decreased in the kidney compared with Sham group. NHERF1 protein expression was signi?cantly increased in RDNX compared with Sham group, whereas NHERF2 protein expression was signi?cantly decreased after renal denervation. Similar results were observed at the mRNA level of NHE1, NHE3, NHERF1 and NHERF2 expression. The present ?ndings suggest that the renal sympathetic nervous system plays a role in the regulation of NHE1 and NHE3 in the kidney of SHR, and NHERF1 may be involved in the expression of NHE3 in the kidney of SHR.     

伊贝沙坦对自发性高血压大鼠肾脏血管紧张素转换酶2基因表达的影响

目的观察自发性高血压大鼠(SHR)肾脏血管紧张素转换酶2(ACE2)的表达,探讨伊贝沙坦对SHR肾脏ACE2 mRNA表达的调节作用。方法20只14周龄雄性SHR分为SHR组和伊贝沙坦组,各10只。伊贝沙坦组每只大鼠予以伊贝沙坦50 mg·kg-1·d-1灌胃,给药时间12周。同时取14周龄雄性京都种Wistar大鼠10只为对照组。SHR组和对照组给予等量蒸馏水灌胃12周。采用免疫组织化学和逆转录聚合酶链反应检测各组大鼠肾脏ACE2表达,利用放射免疫测定法检测各组大鼠血浆血管紧张素(Ang)Ⅱ浓度。结果与对照组比较,SHR组ACE2 mRNA表达显著减少(0．72±0．11对1．11±0．15);与SHR组比较,伊贝沙坦组经12周治疗后,ACE2 mRNA表达明显提高(1．03±0．13对0．72±0．11),均为P<0．05。SHR肾脏ACE2 mRNA表达与血浆AngⅡ浓度成正相关(r=0．83,P<0．05)。结论ACE2在高血压大鼠肾脏表达显著减少,可能是高血压病理生理变化之一。AngⅡ-1型受体阻滞剂伊贝沙坦上调SHR肾组织ACE2 mRNA表达,提示这可能是该药物反向调节过度激活的肾素-血管紧张素系统又一新途径。     

Role of renal alpha 2-adrenergic receptors in spontaneously hypertensive rats

To identify a physiological role for renal alpha 2 adrenergic receptors, renal vascular and tubular responses to administration of graded frequencies of renal nerve stimulation or graded doses of adrenergic agonists were determined in anesthetized spontaneously hypertensive, Wistar-Kyoto, and Sprague-Dawley rats. Renal vasoconstrictor responses to renal nerve stimulation and alpha 1-adrenergic receptor agonists (norepinephrine, phenylephrine) were inhibited by an alpha 1-adrenergic receptor antagonist (prazosin) but not by an alpha 2-adrenergic receptor antagonist (rauwolscine). A semilog plot of renal vasoconstrictor responses a fraction of control renal blood flow versus agonist dose (in nanograms) was linear with the slope, k, taken as the fractional decrease in renal blood flow per nanogram. The alpha 2-adrenergic receptor agonists (clonidine, guanabenz) produced minimal renal vasoconstrictor responses (fractional decrease in renal blood flow per nanogram: norepinephrine, 0.011; phenylephrine, 0.003; clonidine, 0.00087; guanabenz, 0.000037). The small renal vasoconstrictor responses to clonidine and guanabenz were more inhibited by rauwolscine than by prazosin. Low frequency renal nerve stimulation produced antidiuresis and antinatriuresis without decreasing glomerular filtration rate or renal blood flow. The antidiuretic and antinatriuretic responses were inhibited by prazosin but unaffected by rauwolscine. The magnitude of the renal vascular and tubular responses and their adrenergic receptor mediation were not different between spontaneously hypertensive, Wistar-Kyoto, and Sprague-Dawley rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Developmental change of kidney receptor for atrial natriuretic factor in spontaneously hypertensive rat

Properties of human atrial natriuretic factor (ANF) binding to the crude membrane fraction of rat kidney were studied using the ANF-radiolabeled receptor assay; the developmental change of renal ANF receptors in three age groups of spontaneously hypertensive rats (SHR) was also investigated with the methods of radiolabeled receptor assay and the quantitative approach of in vitro macro-autoradiography. Temperature and incubation time greatly influenced ANF binding capacities because of the degradation of radiolabeled ligand. Addition of 5 mM MgCl2 to assay buffer was useful for the stabilization of ANF specific binding. Scatchard analysis suggested that the crude membrane fraction of rat's kidney had a single binding site with the apparent dissociation constant of 0.55 nM. In the study of the developmental change of renal ANF receptor in SHR, systolic blood pressure of the SHR at the age of 5 weeks and 12 weeks was significantly higher than that of age-matched Wistar-Kyoto (WKY) rats, but there was no significant difference in blood pressure between SHR and WKY rats at the age of 3 weeks. Concerning the radiolabeled receptor assay of ANF, the apparent dissociation constant and maximum binding capacity in SHR were low in all age groups when compared with those of WKY rats. In the in vitro macro-autoradiographic observation, the specific binding of ANF was localized mainly in the renal cortex, and these binding patterns of SHR and WKY rats were the same in all age groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hyperprolactinaemia in the spontaneously hypertensive rat.

A hypothalamic role in the aetiology of hypertension in the spontaneously hypertensive rat (SHR) has been suggested by prior observations. In an attempt to determine whether the central control of prolactin (PRL) release is altered in the SHR we have compared the PRL response to immobilization stress, thyrotrophin releasing hormone (TRH), haloperidol, and L-DOPA in the SHR and in normotensive Wistar control rats. Carotid artery catheters were inserted 48 h prior to the PRL response studies and the catheters were maintained patent with heparinized saline. Timed blood samples were obtained in SHR and control rats weighing 180-225 g. The SHR demonstrated elevated basal serum levels of PRL and greater PRL responses to stress. However, administration of L-DOPA resulted in a similar suppression of serum PRL in the SHR and in the normotensive controls. These findings suggest alteration in the central control of PRL release in the SHR. Observations of elevated basal PRL, exaggerated PRL in response to L-DOPA in SHR are consistent with normal pituitary responsiveness to dopamine suppression of PRL release, but defective hypothalamic metabolism of dopamine. Alterations in central dopamine control mechanisms in the SHR may play a role in the pathogenesis of essential hypertension in these animals.     

Insulin resistance in the spontaneously hypertensive rat

To determine experimentally if insulin resistance is associated with spontaneously occurring hypertension, insulin-stimulated glucose metabolism was studied in an animal model of genetic hypertension. The spontaneously hypertensive rat (SHR) and its genetic control, the Wistar-Kyoto strain (WKY) were studied with the euglycemic hyperinsulinemic clamp technique. Clamp studies demonstrated reduced insulin-stimulated glucose uptake in SHR (P less than .001). These data indicate that SHR is insulin-resistant when compared with WKY. A reduction of insulin-stimulated glucose metabolism occurred in older animals of both strains, providing evidence of an aging effect on insulin-stimulated glucose metabolism. However, the reduction of insulin-stimulated glucose metabolism was more pronounced in the hypertensive animals. This study demonstrates the presence of peripheral (skeletal muscle) insulin resistance in the SHR.     

Stimulation of high-affinity adenosine A2 receptors decreases the affinity of dopamine D2 receptors in rat striatal membranes.

Since high-affinity adenosine A2 receptors (A2a) are localized exclusively in dopamine-rich regions in the central nervous system and mediate inhibition of locomotor activity, we have examined the effect of A2a receptor activation on D1 and D2 receptor binding in membrane preparations of the rat striatum. The A2a agonist 2-[p-(2-carboxyethyl)phenethylamino]-5'- N-ethylcarboxamidoadenosine (CGS 21680) increased the Kd of the dopamine D2 agonist L-(-)-N-[3H]propylnorapomorphine without affecting the Bmax. The increase in Kd was maximal (40%) at 30 nM CGS 21680. CGS 21680 (30 nM) decreased the dopamine-induced inhibition of [3H]raclopride (a D2 antagonist) binding due to an increase (about 3-fold) in KH and KL, the dissociation constants of high- and low-affinity binding sites. The effects of CGS 21680 were antagonized by the adenosine antagonist 8-phenyltheophylline (10 microM). (-)-N6-(2-Phenylisopropyl)adenosine produced an effect similar to that of CGS 21680, provided the concentration used was high enough to stimulate A2a receptors (300 nM). GTP (50 microM) also decreased the dopamine-induced inhibition of [3H]raclopride binding but, in contrast to CGS 21680, GTP decreased the proportion of D2 receptors in the high-affinity state. CGS 21680 (30 nM) did not affect the Kd or Bmax of [3H]raclopride and failed to affect ligand binding to D1 receptors. Thus, stimulation of A2a receptors potently reduces the affinity of D2 agonist binding sites within the plasma membrane of striatal neurons. This A2a-D2 interaction may underlie the neuroleptic-like actions of adenosine agonists and the enhancing effects of adenosine antagonists, such as caffeine, on locomotor activity.     

Type 1A dopamine receptor expression in the heart is not altered in spontaneously hypertensive rats

We have recently demonstrated that type 1A dopamine (D_1A) receptor is expressed in the rat heart, but its function still remains unknown. In the present study, we investigated possible changes in the expression level and the distribution of the cardiac D_1A receptor in the development of left ventricular hypertrophy in spontaneously hypertensive rats/Izumo strain (SHR/Izm) at the ages of 4, 8, and 20 weeks. We examined D_1A receptor protein distribution by immunohistochemistry and gene expression by competitive polymerase chain reaction (competitive PCR). In SHR/Izm, compared with the age-matched Wistar Kyoto rats/ Izmo strain (WKY/Izm), blood pressure and heart/body weight ratio were significantly increased at 8 and 20 weeks. By immunohistochemistry, the D_1A receptor was localized in cardiomyocytes and vascular smooth muscle cells of coronary arteries, but not in interstitial fibrotic tissue. D_1A receptor distribution was not changed either by the strain or the age. Competitive PCR analysis showed that the D_1A receptor mRNA level was significantly higher at 4 weeks than at 8 and 20 weeks in both strains of rats and that there was no significant difference in D_1A receptor mRNA between SHR/Izm and WKY/Izm at any age ( 43.2 ± 10.4 attomol × 10⁻³/L v 43.1 ± 11.2 attomol × 10⁻³/L at 4 weeks, P = not significant, 3.9 ± 0.9 attomol × 10⁻³/L v 4.0 ± 1.3 attomol × 10⁻³/L at 8 weeks, P = not significant, 3.0 ± 1.2 attomol × 10⁻³/L v 1.9 ± 1.6 attomol × 10⁻³/L at 20 weeks, P = not significant). These results do not support the hypothesis that changes in D_1A receptor expression are associated with the development of left ventricular hypertrophy in SHR.