Mature Spontaneously Hypertensive Rats Research Articles

Effects of Neuroinflammation and Autophagy on the Structure of the Blood-Brain Barrier in ADHD Model.

Spontaneously hypertensive rats (SHR) are the most common animal model used to study attention deficit hyperactivity disorder (ADHD). The purpose of this study was to look at the impact of neuroinflammation and autophagy on blood-brain barrier function in the prefrontal cortex and hippocampus of ADHD rats. The rats were separated into three groups: juvenile SHR (6weeks), mature SHR (12weeks), and comparable age WKY groups. An open-field test was used to assess rats' ability to move on their own. Immunofluorescence was used to detect the Iba1-immunopositive microglia, ZO-1 and TNF-α. Meanwhile, the expression of p62, Beclin-1, LC3B, and MMP9, MMP2, TNF-α, ZO-1, and occludin were detected by Western blot. The results have shown that Iba1-immunopositive microglia and TNF-α protein in the brain of SHR rats were significantly increased. Moreover, autophagy of cells and the level of MMP2 and MPP9 in the prefrontal cortex and hippocampus increased in SHR rats. In addition, the expression of ZO-1 and occludin was decreased in SHR rats. To sum up, the increase of neuroinflammation and excessive autophagy were essential factors for the damage of blood-brain barrier structure and function.

The cytokine alterations/abnormalities and oxidative damage in the pancreas during hypertension development

The aim of the present study was to compare the content of cytokines, chemokines, and oxidative stress markers in the pancreas of spontaneously hypertensive rats (SHRs) and Wistar Kyoto Rats (WKYs) serving as controls. Enzyme-like immunosorbent assay (ELISA) and biochemical methods were used to measure pancreatic levels of interleukin-1ß, interleukin-6, tumor necrosis factor α, transforming growth factor β, RANES, monocyte chemoattractant protein 1, interferon gamma-induced protein 10, malondialdehyde, and sulfhydryl groups. The results showed that the pancreatic concentrations of all studied cytokines and chemokines did not differ between 5-week-old SHRs and WKYs, except RANTES which was significantly reduced in juvenile SHRs. In 10-week-old animals, except interleukin-1ß, the levels of all these proteins were significantly reduced in SHRs. The pancreatic levels of malondialdehyde were significantly reduced in 5-week-old SHRs and significantly elevated in 10-week-old SHRs while the contents of sulfhydryl groups were similar in both rat strains at any age studied. In conclusion, these data provide evidence that in maturating SHRs, the pancreatic levels of cytokines and chemokines are significantly reduced, while malondialdehyde significantly elevated. This suggests that in the pancreas of mature SHRs, the inflammation process is suppressed but there is ongoing oxidative damage.

The effect of CpG-rich DNA fragments on the development of hypertension in spontaneously hypertensive rats (SHR)

In this study we have investigated properties of blood plasma extracellular DNA (cell-free DNA, cfDNA) from patients with essential arterial hypertension (AH). Concentration of cell-free DNA was basically the same as in healthy donors, however, the content of the marker, CpG-rich cell-free DNA fragments (CpG-DNA) of the transcribed area of the ribosomal repeat (TArDNA, CpG-DNA) was higher in AH patients. For evaluation of the effect of CpG-DNA on the development of arterial hypertension 2-day-old SHR rat pups and corresponding controls of normotensive WKY rats received a single subcutaneous injection of human TArDNA (700 ng) to generate anti-CpG-DNA antibodies (and thus to alter the CpG-DNA content in total cfDNA). After 9 weeks blood pressure (BP) in SHR rats immunized with CpG-DNA was significantly lower than in control SHR rats and was basically the same as in WKY rats. However, subsequently, BP of the immunized SHR exhibited age-related increase, which reached the stably high values typical for mature SHR 8 weeks later compared with control SHR. Analysis of cfDNA has shown that in 17-week-old immunized SHR rats concentrations of cell-free DNA and its small DNA fragments are lower and the content of CpG-DNA (rat TArDNA) is higher than in corresponding controls. These changes were accompanied by a 3.5-fold increase in blood endonuclease activity and the decrease in content of free (unbound to cfDNA) anti-CpG-DNA antibodies. Total content of anti-CpG-DNA antibodies in the immunized rats was the same as in control animals. Thus, the delayed age-related increase in stable BP observed in immunized SHR rats is obviously not associated with increased generation of anti-CpG-DNA antibodies. Possible reasons of this effect are discussed.

Impaired Erythrocyte Filterability of Spontaneously Hypertensive Rats: Investigation by Nickel Mesh Filtration Technique

Deformability of erythrocytes plays a key role in the impairment of the microcirculation in hypertension. However, erythrocyte deformability in spontaneously hypertensive rats (SHR) during development of hypertension has not been fully investigated so far. Erythrocyte filterability (whole cell deformability) was investigated in relation to blood pressure measured by the tail-cuff method in SHR and age-matched Wistar-Kyoto rats (WKY), using a highly sensitive and reproducible nickel mesh filtration technique. Impaired erythrocyte filterability was marked (37.0+/-17.5%) in prehypertensive young SHR (7 weeks of age) and sustained (51.6+/-13.3%) in hypertensive mature SHR (18 weeks of age), when compared with that of age-matched WKY (62.1+/-7.2% in 7 weeks of age, P<0.005, and 71.1+/-3.9% in 18 weeks of age, P<0.005, respectively). This impairment in SHR could not be explained by the mean corpuscular volume or mean corpuscular hemoglobin concentration of erythrocytes, but the erythrocyte count was significantly (P<0.005) greater in SHR than in the age-matched WKY. Although the precise mechanisms remain to be elucidated, markedly impaired erythrocyte filterability in SHR is considered to contribute to the development and maintenance of genetic hypertension. (Circ J 2010; 74: 129 - 136).

Increased spontaneous tone in renal arteries of spontaneously hypertensive rats

The spontaneous tone of vascular smooth muscle is augmented in hypertension. The present study examined the role of nitric oxide (NO), cyclooxygenase (COX), thromboxane A(2)/prostanoid (TP) and PGE(2)/prostanoid (EP-1) receptors, reactive oxygen species, and large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels in the regulation of spontaneous tone in renal arteries of young and mature Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Rings of arteries, with and without endothelium, were suspended in a myograph for isometric force recording. Spontaneous tone (increase above initial tension) was observed only in arteries of mature SHR and was greater in arteries without endothelium. N(omega)-nitro-L-arginine methyl ester (L-NAME, an inhibitor of NO synthases) induced larger contractions in arteries of SHR than WKY. Indomethacin (a COX inhibitor), SC-19220 (an EP-1 receptor antagonist), and terutroban (a TP receptor antagonist) reduced the L-NAME-evoked contractions. Tiron (a superoxide anion scavenger), catalase (an enzyme that degrades H(2)O(2)), and deferoxamine (a hydroxyl radical scavenger) augmented the L-NAME-induced contractions in arteries of mature SHR. Charybdotoxin (a BK(Ca) channel blocker) caused contractions in arteries of mature SHR without endothelium and in arteries with endothelium incubated with L-NAME. A decreased protein level of endothelial NO synthase, an increased release of prostacyclin, and an increased expression of EP-1 receptors were observed in arteries of mature SHR. The present study suggests that spontaneous tone is precipitated by age and hypertension. The reduced production of NO, leading to decreased activation of BK(Ca) channels, may leave the actions of endogenous vasoconstrictors unopposed. COX products that activate EP-1 and TP receptors are involved in the development of spontaneous tone.

Ischemic preconditioning is lost in aging hypertensive rat heart: Independent effects of aging and longstanding hypertension

Although in experimental hypertension the cardioprotective effects of ischemic preconditioning (PC) appear to be maintained, most studies have examined the short-term hypertension in juvenile animals. However, aging may be an additional factor that influences the effectiveness of PC. The aim of this study was to characterise the effects on PC of LVH and aging simultaneously. Hearts from spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar–Kyoto rats (WKY) were studied. Excised hearts were Langendorff-perfused to give equivalent coronary flow per gram heart weight. The left main coronary artery was occluded for 35 min followed by 120 min reperfusion. Infarct size was determined by tetrazolium staining. Heart size was assessed as left ventricle/body weight ratio (LV/BW). PC was effected with 2 × 5 min periods of global ischemia prior to coronary occlusion. Hearts were studied at 3–4 months (juvenile), 7–8 months (mature) or 12–13 months (aging). LV/BW ratio in SHR increased relative to WKY controls by 20%, 32% and 40% in juvenile, mature and aging hearts, respectively, but ischemic risk zone size was similar in all groups (52–59% of LV). PC was equally effective at limiting infarct size in juvenile and mature SHR and WKY hearts but was ineffective in aging hearts from both WKY and SHR. Since angiotensin-converting enzyme inhibitors enhance sub-threshold PC in normal myocardium, we also examined the action of captopril (Cap) in aging hearts. Additional aging hearts received treatment with Cap 200 μM as an adjunct to PC. Although Cap + PC was able to induce modest protection in aging WKY hearts, this was not seen in aging SHR hearts. We conclude that PC is lost in longstanding hypertension through independent contributions of both hypertension and aging. These findings may have implications for the clinical development of preconditioning-based therapies since elderly patients with longstanding hypertension are at high risk of developing ischemic heart disease.

Abnormal Renovascular Parathyroid Hormone-1 Receptor in Hypertension: Primary Defect or Secondary to Angiotensin II Type 1 Receptor Activation?

We previously reported that PTHrP-induced renal vasodilation is impaired in mature spontaneously hypertensive rats (SHR) through down-regulation of the type 1 PTH/PTHrP receptor (PTH1R), a feature that contributes to the high renal vascular resistance in SHR. Here we asked whether this defect represents a prime determinant in genetic hypertension or whether it is secondary to angiotensin II (Ang II) and/or the mechanical forces exerted on the vascular wall. We found that the treatment of SHR with established hypertension by the Ang II type 1 receptor antagonist, losartan, reversed the down-regulation of PTH1R expression in intrarenal small arteries and restored PTHrP-induced vasodilation in ex vivo perfused kidneys. In contrast, the PTH1R deregulation was not found in intrarenal arteries isolated from prehypertensive SHR. Moreover, this defect, which is not seen in extrarenal vessels (aorta, mesenteric arteries) from mature SHR appeared kidney specific in accordance with the acknowledged enrichment of interstitial Ang II in this organ and its enhancement in SHR. In deoxycorticosterone-acetate-salt rats, an Ang II-independent model of hypertension, renovascular PTH1R expression and related vasodilation were not altered. In SHR-derived renovascular smooth muscle cells (RvSMCs), the PTH1R was spontaneously down-regulated and its transcript destabilized, compared with Wistar RvSMCs, both effects being antagonized by losartan. Exogenous Ang II elicited down-regulation of PTH1R mRNA in RvSMCs from Wistar rats. Together, these data demonstrate that Ang II acts via the Ang II type 1 receptor to destabilize PTH1R mRNA in the renal vessel in the SHR model of genetic hypertension. This process is kidney specific and independent from blood pressure increase.

Unique levels of expression of N-methyl- d-aspartate receptor subunits and neuronal nitric oxide synthase in the rostral ventrolateral medulla of the spontaneously hypertensive rat

The rostral ventrolateral medulla (RVLM) is the major brainstem region contributing to sympathetic control of blood pressure. We have compared the expression of N-methyl- d-aspartate (NMDA) receptor subunits (NR1, NR2A–D), NR1 splice variants (NR1-1a/1b, -2a/2b, -3a/3b, -4a/4b), and the neuronal and inducible isoforms of NO synthase (nNOS and iNOS) in the RVLM of Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR), based on the hypothesis that altered NMDA receptor make-up or altered expression of endogenous NO may be associated with the increase in sympathetic output described from this site in hypertension. Total RNA was extracted and reverse transcribed from the RVLM of mature male WKY and SHR (16–23 weeks). Conventional polymerase chain reaction (PCR) indicated that only the NR1 splice variants NR1-2a, NR1-2b, NR1-4a and NR1-4b were expressed in the RVLM of either species. Quantitative real-time PCR indicated that for both strains of rat, mRNA for the NR1 subunit (all splice variants) was the most abundant (16.5-fold greater, P≤0.05, relative to the NR2A subunit). Amongst the NR2A–D subunits, NR2C was the most abundant (7- and 1.7-fold greater relative to the NR2A subunit, P≤0.05, WKY and SHR, respectively). Relative to WKY, mRNA levels for the NR2C and NR2D subunits in the SHR RVLM were significantly lower (0.3- and 0.25-fold less, P≤0.05), while nNOS was significantly higher (1.76-fold greater, P≤0.05). This was confirmed immunohistochemically for nNOS expression. These results demonstrate differential expression levels of NMDA receptor subunits and NOS isoforms in the RVLM region of SHR when compared to WKY rats.

Enhancement of glucocorticoid and mineralocorticoid receptor density in the microcirculation of the spontaneously hypertensive rat.

Elevated blood pressure and abnormal physiological parameters in the microcirculation of the spontaneously hypertensive rat (SHR) can be normalized by adrenalectomy. Thus glucocorticoids and mineralocorticoids may have major control over blood pressure status and organ injury mechanisms in SHRs. As background, this study was designed to examine the distribution of the glucocorticoid and mineralocorticoid receptors in a microvascular network. Mature SHR and their normotensive controls, the Wistar-Kyoto (WKY) rat, were studied. An immunohistochemical method was developed that provides a comprehensive display of the receptors in all segments of the mesentery microcirculation and the surrounding tissue parenchyma. All cells in the mesentery exhibit immunolabeling of the glucocorticoid receptor with predominant expression in the nuclei of parenchymal and endothelial cells. The mineralocorticoid receptor is expressed also in most cells of the microcirculation and adjacent parenchymal tissue. Both receptors exhibit the highest levels of immunolabel in the wall of the arterioles and venules, with lower levels in capillaries. Compared with WKY rats, the SHRs exhibit significantly enhanced density of glucocorticoid and mineralocorticoid receptors in endothelial cells of arterioles and venules as well as in parenchymal cells. These results suggest that the enhanced sensitivity of the SHR to glucocorticoids and aldosterone may be in part associated with enhanced glucocorticoid and mineralocorticoid receptor densities in the microcirculation.

Microvascular cell death in spontaneously hypertensive rats during experimental inflammation.

Chronic hypertension is associated with an increased risk for tissue injury that may be mediated in part by endothelium and inflammatory cells. To clarify a possible underlying mechanisms, we examined leukocyte migration in the microcirculation and concomitant parenchymal cell death. The mesentery of spontaneously hypertensive rats (SHRs) and their normotensive controls, Wistar Kyoto (WKY) rats, was examined with digital fluorescence microscopy after topical stimulation with an inflammatory mediator (f-met-leu-phe, 10(-8)M). The migratory pathways of individual leukocytes were traced, and at the same time cell death was detected by use of a life-death indicator (propidium iodide) over a period of 3 hours. Both WKY and SHR had a progressively increasing number of leukocytes migrating across the endothelium in postcapillary venules into the tissue parenchyma. But parenchymal cell death was detected in a random pattern in the mesentery tissue, without correlation to the migratory positions of the leukocytes. Although mature SHR rats (about 17 weeks) exhibited the same level of cell death as age-matched WKY rats, older WKY rats (about 30 weeks) had significantly lower levels of cell death, whereas the SHR rats maintained the same number of parenchymal cell death as mature animals. These results suggest that in the presence of an inflammatory mediator, the SHR may exhibit a stronger response to an inflammatory mediator than normotensive WKY rats in a fashion that is age, but not blood pressure, dependent. Parenchymal cell death does not correlate with migration of activated leukocytes at the microvascular level.

Neurotrophin 3 is increased in the spontaneously hypertensive rat

To determine whether the noradrenergic sympathetic hyperinnervation in the spontaneously hypertensive rat (SHR), a genetic model of essential hypertension, is associated with changes in neurotrophin 3 (NT3) concentrations. NT3 levels were measured using a sensitive enzyme-linked immunosorbent assay (ELISA) in the superior cervical ganglia (SCG), heart, mesenteric artery (MA) and blood of postnatal and mature SHR and normotensive Wistar-Kyoto (WKY) rats. NT3 levels in SHR are significantly higher in the SCG during the first 4 postnatal weeks, and in the heart and MA from 2 to 10 weeks of age, compared with levels in WKY rats. The elevated NT3 found in the sympathetic ganglia and hyperinnervated organs of SHR indicates that NT3 may play an important role in the development of hyperinnervation, possibly by enhancing the survival and/or nerve sprouting of sympathetic neurons.

Spontaneously hypertensive rats: a potential model to identify drugs for treatment of learning disorders.

Spontaneously hypertensive rats (SHR) of 3 to 12 months of age learned and retrieved less information than normotensive Wistar-Kyoto rats (WKY), although no difference was found with animals from 18 and 24 months of age. The combined influence of hypertension and aging had an additive detrimental effect on cognitive functions. Notwithstanding these deficiencies in learning and memory, SHR have seldom been used as a model in the screening of drugs with therapeutic potential for treatment of disorders of cognitive processes. Moreover, the calcium channel blocker nimodipine has beneficial effects on learning in both aged and hypertensive animals and humans. However, no attempt has been made to investigate whether nimodipine can reverse the additive deleterious effects of aging and hypertension in the same subject. We recently reported that deteriorated animals (middle-aged and/or hypertensive) chronically treated with nimodipine (via osmotic minipumps) exhibit higher learning scores. This information indicates that nimodipine can reverse the impairing effects of either aging or hypertension on learning; the presence of the two conditions, however, produces a severe impairment that can be partially reversed by this drug. Therefore, we propose that mature and middle-aged SHR represent a model for the screening of potentially useful drugs in the treatment of learning disorders, probably associated with hypertension and/or aging. Nevertheless, it must be remembered that the SHR is a genetic model and the appearance of neural disturbances could be a parallel genetic phenomenon and not necessarily or exclusively related to hypertension per se.

Platelet Thrombus Formation in Microvessels of Young Spontaneously Hypertensive Rats

We have previously shown an increase in platelet-to-endothelial cell adhesion in microvessels of spontaneously hypertensive rats (SHR) during the established stage of hypertension (12 weeks). The objective of the current study was to determine if the platelet-to-endothelial cell interaction would be altered in the early developmental phase of hypertension. Male weanling (3 weeks old) SHRs (n=6) and age matched normotensive Wistar-Kyoto (WKY) rats (n=6) were used to study platelet thrombus formation. Intravascular fluorescein isothiocyanate tagged to bovine serum albumin was activated with 450-490 nm light to induce thrombus formation in microvessels. Plasma concentrations of von Willebrand factor (vWF), fibrinogen and fibronectin (FN) were measured in rats during both early (3 week) and established stages of hypertension development. Thrombus initiation time in both arterioles (847+/-85 sec) and venules (222+/-40 sec) of young SHRs was significantly shorter (p<0.05) than in arterioles (1270+/-88 sec) and venules (630+/-72 sec) of age matched WKY rats respectively. After thrombus appearance, however, overall time for vessel occlusion in arterioles (2590+/-90 sec) and venules (935+/-131 sec) of SHRs was not different compared to that in arterioles (2650+/-191 sec) and venules (1240+/-93 sec) of age matched WKY rats. The plasma concentration of FN was increased (p<0.05) in both the young (0.9+/-0.1 mg/ml) and mature (1.1+/-0.2 mg/ml) hypertensive rats (n=5) compared to that in young (0.6+/-0.03 mg/ml) and mature (0.5+/-0.1 mg/ml) WKY rats (n=5), while fibrinogen content (3.6 +/-0.3 mg/ml) was elevated (p<0.05) only in mature SHRs (n=5) compared to that (2.7+/-0.02 mg/ml) in age matched WKY rats (n=5). The plasma concentration of vWF was similar to that of controls in either age group of hypertensive animals. These results suggest that changes in platelet-to-endothelial cell interactions occur in the early phase of genetic hypertension development in rats, and appears to result from alteration of plasma concentration of adhesion proteins.

Hypothalamic Hypertensive Factor

Abstract Human and rat plasma and rat hypothalamus contain a cytochemically detectable substance, the concentration of which rises with an increase in salt intake. The plasma concentration of this material is also raised in essential hypertension and in the spontaneously hypertensive rat (SHR), the Milan hypertensive rat, and the reduced renal mass (RRM) hypertensive rat. In the normal rat, the greatest concentration is found in the hypothalamus of the SHR and the RRM hypertensive rat. The physicochemical characteristics of this cytochemically detectable hypothalamic hypertensive factor (HHF), including chromatographic behavior and molecular weight range, suggest that it may share features common to a substituted guanidine that is present in established nitric oxide synthase (NOS) inhibitors. It was therefore decided to determine the effect on NOS activity of the HHF obtained from mature SHR. The ability of HHF to inhibit NOS activity was studied on (1) NOS extracted from bovine aorta, rat brain, and human platelets by measuring the conversion of radiolabeled l- arginine to l -citrulline and (2) rat liver NOS measured indirectly with a cytochemical technique based on the stimulation of soluble guanylate cyclase activity in hepatocytes by NO. HHF showed a biphasic inhibitory action on platelet NOS activity that was greater with HHF obtained from SHR than from Wistar-Kyoto rats. HHF also had a biphasic inhibitory effect on hepatocyte NOS activity that was more potent when obtained from SHR. It is proposed that the increase in HHF, a novel form of NOS inhibitor that is elevated in SHR, may be involved in the rise in arterial pressure.

Increased expression of parathyroid hormone-related peptide gene in blood vessels of spontaneously hypertensive rats.

We have shown recently that mechanical stretch of cultured rat aortic smooth muscle cells induces a marked increase in gene expression of the vasorelaxant parathyroid hormone-related peptide. In the present study, we investigated whether mechanical force affected the in vivo parathyroid hormone-related peptide gene expression in blood vessels. Northern blot analysis revealed that stretch of isolated rat aortic strips increased the expression level of parathyroid hormone-related peptide mRNA. The parathyroid hormone-related peptide transcript level in aorta and mesenteric vessels from 18-week-old spontaneously hypertensive rats (SHR) was 2.5- and 2.2-fold higher, respectively, compared with age-matched Wistar-Kyoto (WKY) controls, whereas the parathyroid hormone-related peptide mRNA level in aorta from normotensive 4-week-old SHR was similar to that of age-matched WKY controls. The aortic parathyroid hormone-related peptide content was higher in 18-week-old SHR than in age-matched WKY controls. Moreover, treatment of mature SHR with an angiotensin II type 1 receptor antagonist or hydralazine caused a concomitant decrease in the parathyroid hormone-related peptide transcript level in aorta with lowering of blood pressure. These results suggest that the in vivo parathyroid hormone-related peptide gene expression in blood vessels is under the control of mechanical force, pointing to a role of parathyroid hormone-related peptide in the regulation of vascular tone.

Effects of Age on Ca 2+ Currents in Small Mesenteric Artery Myocytes From Wistar-Kyoto and Spontaneously Hypertensive Rats

The purpose of this study was to test the hypothesis that differences in voltage-gated Ca2+ channels increase with age during the development of sustained hypertension in the spontaneously hypertensive rat (SHR). Using patch-clamp methods, we measured whole-cell Ca2+ currents in freshly isolated myocytes from small mesenteric arteries of juvenile (5 to 7 weeks), young (10 to 12 weeks), and mature (19 to 23 weeks) Wistar-Kyoto rats (WKY) and SHR. Indirect tail artery systolic pressure increased progressively with age in SHR (from 125 +/- 5 to 159 +/- 5 to 192 +/- 5 mm Hg) but only in the younger WKY (from 107 +/- 6 to 130 +/- 4 to 136 +/- 4 mm Hg). Peak Ca2+ current density (current per cell capacitance) was larger in SHR than WKY myocytes at all ages (at 6 weeks, 3.5 +/- 0.4 versus 2.3 +/- 0.2 pA/pF; at 12 weeks, 3.8 +/- 0.2 versus 3.1 +/- 0.2; at 20 weeks. 4.9 +/- 0.4 versus 3.3 +/- 0.4). Cell capacitance (surface area) was significantly smaller in 12-week-old SHR than WKY (25.2 +/- 1.1 versus 31.8 +/- 1.6 pF), but no differences were found in the 6- or 20-week-old groups. There were significant differences in Ca2+ current with strain, age, and voltage but no significant age-strain interactions. The ratio of peak Ca2+ current for SHR to that of WKY declined linearly with voltage at all ages suggesting differences in the voltage dependence of Ca2+ current activation. The voltage dependence of Ca2+ current was shifted to the left in SHR compared with WKY at all ages. Activation curves were shifted significantly in the negative-voltage direction only in 20-week-old SHR myocytes. We have found differences with age in Ca2+ current density and its voltage dependence in SHR compared with WKY during the phase of development in which blood pressure becomes established in the SHR. The net effect of these differences predicts a larger Ca2+ current in SHR at voltages in the physiological range of membrane potential.

The SHR as a Small Animal Model for Radiocontrast Renal Failure. Relation of Nephrotoxicity to Animal's Age, Gender, Strain, and Dose of Radiocontrast

The male spontaneously hypertensive rat (SHR), as it ages, suffers many of the renal and cardiovascular complications that are recognized in humans as risk factors for radiocontrast (RC) agent induced renal failure (RF). Knowledge of this led us to test this strain of rats as a small animal model for RC-induced renal failure (RC-RF). Functional studies demonstrated a significant fall in GFR in the recovery period after RC administration. In addition, histopathologic evaluation of the kidneys was done in this study. Our results are based on assigning separate scale values to the histopathological evaluation of the (a) glomeruli, (b) tubules, (c) interstitium, and (d) arteries and arterioles of the kidneys. Saline (S) was administered to one group and the RC agent Hypaque-76 (diatrizoate meglumine sodium) to paired groups of 5-, 8-, 10-, 12-, and 14-month-old male SHR. The results indicated that younger animals (5 and 8 months old) were resistant to the nephrotoxic effects of the RC, but developed susceptibility at 10 months of age, when spontaneous renal pathology became manifest. Both spontaneous renal pathology and RC-induced renal damage (RC-RD) increased as the animals aged. In addition, when the administered dose of RC was repeated after a short interval of only 6 h, the degree of RC-RD increased greatly. In parallel control studies of the influence of gender and strain on the response to RC in 12-month-old rats, neither hypertensive female SHR nor male normotensive Wistar-Kyoto (WKY) rats demonstrated significant spontaneous renal pathology or the marked susceptibility to RC nephrotoxicity shown by their male SHR counterparts.This small animal model for RC-RD, the mature male SHR, has the distinct advantage that risk factors for RC-RD, similar to those characterized in humans for RC-RF, develop spontaneously without requiring any special treatment or surgical intervention.

Spontaneously hypertensive rats are resistant to the development of hypercholesterolemia

The arterioles of young spontaneously hypertensive rats (SHR) are purported to have an enhanced sensitivity to nitric oxide (NO)-dependent vasodilators, relative to normotensive animals, while NO-related arteriolar responses are diminished in both mature SHR as well as hypercholesterolemic normotensive rats. Because endothelial production of NO relaxes vascular smooth muscle and inhibits platelet adhesion and aggregation, hypercholesterolemia may synergistically affect the development of genetic hypertension. The NO-mediated baseline vascular tone, acetylcholine-induced dilation, and inhibition of platelet thrombus formation were studied over time (10 weeks) in SHR and hypercholesterolemic SHR (HC-SHR). The in vivo microcirculation of the cremaster muscle was used to quantitate all observations. The HC-SHR became significantly hypercholesterolemic after 1 week on the cholesterol-supplemented diet, with serum cholesterol concentrations remaining elevated for the 10 weeks studied. However, the serum cholesterol concentrations of HC-SHR were significantly less than those of Sprague-Dawley and Wistar-Kyoto rats fed the same diet. Dietary hypercholesterolemia did not exacerbate the development of genetic hypertension. Second- and third-order arterioles of SHR and age-matched HC-SHR constricted to the same extent when the NO synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) was applied. The third order arterioles of both groups also dilated the same amount to acetylcholine and sodium nitroprusside. Platelet thrombus formation induced by light/dye photochemistry was not different between the SHR and HC-SHR groups either at 1 or 10 weeks of diet, and L-NAME decreased the time to thrombus occlusion of blood flow equally in both groups. This is in marked contrast to the previously reported hypercholesterolemia-induced decreases in vascular reactivity in Sprague-Dawley rats. These current findings demonstrate that SHR are resistant to the development of hypercholesterolemia and that NO-mediated vascular responses in SHR are not attenuated by hypercholesterolemia.

Altered blood pressure, renal tubular function and levels of circulating inhibitors of Na-K-ATPase in mature SHR exposed to low salt diet in the perinatal period.

1. It has been shown previously that low salt diet, confined to the perinatal period only, reduces blood pressure (BP) and sodium retention in spontaneously hypertensive rat (SHR) offspring at maturity when compared with those given high salt diet. 2. In this study it is shown that such high salt diets are associated with an increased level of circulating Na-K-ATPase inhibitor (CINK) activity. 3. Animals given perinatal high salt diet have a significantly greater tubular reabsorptive capacity when compared with those given low salt diet. 4. The finding of a high level of circulating Na-K-ATPase inhibitory material in the face of increased renal tubular capacity and blood pressure suggests that while this inhibitory material may play a role in the elevated blood pressure of animals given high salt diet, it cannot cause the elevated rate of fluid reabsorption.

Decreased arteriolar endothelium-derived relaxing factor production during the development of genetic hypertension.

In the present study, basal and stimulated production of endothelium-derived relaxing factor (EDRF) were examined in young (4-5 week-old) and mature (10-12 week-old) spontaneously hypertensive rats (SHR) and were compared with those of age-matched Wistar Kyoto (WKY) normotensive rats. Nw-nitro-L-arginine methyl ester (L-NAME) was used as a probe for basal EDRF production in vivo. We also determined the dose-response effects of acetylcholine (Ach, 10(-9)-10(-5) M), sodium nitroprusside (NP, 10(-9)-10(-5) M), and norepinephrine (NE, 3 x 10(-10)-10(-6) M), on third-order arterioles (3A) in the two age groups. Relaxation of 3A vessels in response to Ach was significantly lower (p < 0.01) in mature SHR than in WKY rats. No significant differences were observed in responses to Ach in young animals or in responses to NP in either age groups. Preincubation with L-NAME (2 x 10(-4) M) shifted the dose-response curves of NE to the left in mature WKY rats (n = 6), but not in mature SHR (n = 6). These data indicate that both basal and stimulated production of EDRF are decreased in small arterioles in the striated muscle microcirculation at an established stage of genetic hypertension. These data suggest that a diminished EDRF response by arterioles may be in part responsible for the elevated microvascular reactivity observed in genetic hypertension.