Spontaneously Hypertensive Animals Research Articles

Stress-induced Per1 expression in the brain is altered in hypertensive rats

Hypertension (HTN) is an increasingly prevalent cardiovascular disorder that influences patients’ lives and adds a significant burden to the healthcare system. Stress may contribute to the development of HTN through various mechanisms, including repeated blood pressure elevations and the secretion of vasoconstricting hormones. Individuals with HTN, conversely, may have altered responses to stress. The goal of this study was to determine how neurological responses to control, acute stress and repeated stress conditions are affected by pre-existing HTN. We evaluated the activation of brain regions involved in neuroendocrine and cardiovascular control (i.e., the paraventricular [PVN] and dorsomedial [DMH] hypothalamic nuclei) by quantifying neurons expressing period-1 (Per1) and Fos in these regions. We hypothesized that pre-existing HTN would reduce the basal number of activated PVN and DMH neurons under non-stressed control conditions, but would enhance the activational response to acute emotional stress. We further hypothesized that animals with HTN would demonstrate exaggerated responses to repeated stress exposure. Adult male rats of the normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) strains were exposed to acute (30min x 1d) or repeated (30min x 14d) restraint stress near the beginning (0900h) of their light cycle. Rats were perfused with paraformaldehyde and coronal brain sections (30μm) collected and immunohistochemically stained for Per1 and Fos. Stained cells were quantified by ImageJ analysis of digitally-captured photomicrographs. Cell counts were taken from 5 or 4 sections throughout the rostrocaudal extent of the PVN or DMH, respectively, and compared by t-test with significance determined at p≤0.05. Acute restraint stress significantly increased the number of Fos-expressing neurons, compared to control levels, in the PVN and DMH of both WKY and SHR animals. In both strains, repeated exposure to restraint led to a habituated Fos response. Per1 expression showed a similar pattern in the SHR PVN, but neither acute nor repeated stress altered Per1 expression in the PVN of WKY rats. Interestingly, Per1 expression in the DMH varied by strain and treatment group. Control levels of Per1 in SHR were significantly reduced compared to WKY. Acute restraint reduced the number of Per1-positive neurons in WKY but not in SHR. Following repeated restraint, the number of Per1-expressing neurons was restored to control levels in WKY but was elevated in SHR to a level significantly greater than control. Our data indicate that pre-existing HTN impacts how stress is processed in the brain. More specifically, while chronic or repeated stress is known to have negative health consequences, our findings suggest that acute stress may be of greater concern to hypertensive individuals. This project was supported in part by NIH Grant 5G12RR008124. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Estrogen depletion modulates aortic prothrombotic signaling in normotensive and spontaneously hypertensive female rats

AimIn this study, we investigated how platelets and aorta contribute to the creation and maintenance of a prothrombotic state in an experimental model of postmenopausal hypertension in ovariectomized rats. MethodsBilateral ovariectomy was performed in both 14-week-old female spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats. The animals were kept in phytoestrogen free diet. Vascular parameters, platelet, coagulation and aortic prothrombotic functions and mechanisms were assessed. ResultsExacerbated platelet aggregation was observed in both SHR and WKY animals after ovariectomy. The mechanism was related to aortic COX2 downregulation and reduction in AMP, ADP, and ATP hydrolysis in serum and platelets. A procoagulant potential was observed in plasma from ovariectomized rats and this was confirmed by kallikrein and factor Xa generation in aortic rings. Aortic rings derived from ovariectomized SHR presented a greater thrombin generation capacity compared to equivalent rings from WKY animals. The mechanism involved tissue factor and PAR-1 upregulation as well as an increase in extrinsic coagulation and fibrinolysis markers in aorta and platelets. Aortic smooth muscle cells pre-treated with a plasma pool derived from estrogen-depleted animals developed a procoagulant profile with tissue factor upregulation. This procoagulant profile was dependent on inflammatory signalling, since NFκB inhibition attenuated the procoagulant activity and tissue factor expression. ConclusionsA prothrombotic phenotype was observed in both WKY and SHR ovariectomized rats being associated with platelet hyperreactivity and tissue factor upregulation in aorta and platelets. The mechanism involves proinflammatory signalling that supports greater thrombin generation in aorta and vascular smooth muscle cells.

Intermittent Functioning of Baroreflex Contributes to the Etiology of Hypertension in Spontaneously Hypertensive Rats

The potential roles of the baroreflex in long‐term arterial blood pressure (BP) regulation and in the etiology of primary hypertension have been long debated. We have hypothesized that aging‐associated stiffening of large arteries desensitizes baroreceptors in the aortic arch and carotid sinus, and thereby may contribute to a mechano/neurogenic etiology. To test that hypothesis, we obtained long time‐course continuous arterial pressure data in spontaneously hypertensive (SHR) and control Wistar‐Kyoto (WKY) rats at various ages (7–15 weeks) during the development of the hypertensive phenotype in the SHR animals. Rather than the expected simple proportional relationship between arterial vessel distensibility and baroreflex gain, analysis of data from these animals reveals a markedly intermittent functioning of the baroreflex arc, with long periods (up to several minutes long) with arterial pressure fluctuations coupled to corresponding physiological responses in heart rate and with similarly long periods where the pressure and heart rate fluctuations are not coupled. Several potentially important trends are observed to be associated with the intermittent apparent baroreflex “on” and “off” time periods: (1.) during normal dark‐cycle recording the fraction of time for which the baroreflex is operating in the “on” state ranges from 45–70% for both strains and all ages observed; (2.) the fraction of time in the “on” state decreases with age in both the SHR and WKY strains; (3.) the mean arterial pressure is tightly correlated with fractional “on” time in all rats (see figure ); (4.) mean pressures during “off” states are higher than during “on” states for both strains, both sexes, and at all ages studied; and (5.) mean pressure tends to decrease during “on” states and rise during “off” states in WKY rats, while mean pressure remains elevated at all times in SHR rats. From these observations we hypothesize that impaired function of the baroreflex in the SHR strain contributes to the SHR hypertensive phenotype. This impaired function is reflected in less frequently coupled “on” function in the SHR compared to the WKY and the inability of the functioning baroreflex to reduce pressure during “on” states in the SHR.Support or Funding InformationSupported by NIH grant HL139813Correlation between mean arterial pressure and fractional baroreflex “on” time in SHR and WKY rats.Figure 1

The peroxisome proliferator-activated receptor gamma agonist pioglitazone improves nitric oxide availability, renin-angiotensin system and aberrant redox regulation in the kidney of pre-hypertensive rats.

The peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-dependent nuclear receptor. It plays an important role in kidney physiology, where it might contribute to arterial blood pressure regulation and hypertension development by modulation of several signaling pathways. In our study we focused on the effect of PPARγ agonist pioglitazone on changes in the nitric oxide synthase (NOS) expression and activity, the renin-angiotensin system (RAS) cascade, and redox homeostasis signaling pathways in the renal cortex of young pre hypertensive rat models. Young (5-weeks old) spontaneously hypertensive (SHR) and borderline hypertensive (BHR) rats were treated by pioglitazone (PIO, 10 mg/kg/day) during 10 days. Blood pressure (BP) was determined by plethysmography method. Changes in lipid profile were detected in plasma with standard kits using biochemical analyser. Gene expression has been detected by qRT-PCR and protein level was determined using Western blot analysis. Superoxide dismutase (SOD) and catalase (CAT) activities were determined spectrophotometrically and the total enzyme activity of NOS was measured using a radioactive assay based on conversion of [3H] L-arginine to [3H] L- citrulline. Administration of pioglitazone decreased BP in BHR and slowed down the development of BP increase in young SHR animals. For NOS, activation by PPARγ correlated with increase in gene and protein expression of NOS isoforms and in total enzyme activity both in BHR and SHR. In the AT1R/Nox pathway, the treatment did not significantly influence mRNA expression of the p22phox subunit of NADPH oxidase (Nox) and AT1R, but up-regulated the 'pro-vasodilatatory' Mas and AT2R receptors in both BHR and SHR groups. Pioglitazone treatment affected redox regulation. Increase in gene expression of nuclear factor E2-related factor 2 (Nrf2) and SOD isoforms correlated with SOD and CAT enzyme activities. The group treatment-to-control ratios, BHR Pioglitazone to BHR control and SHR Pioglitazone to SHR control for gene expression increased by 10% to 230%. The largest effect of PPARγ has been observed in SOD1, SOD3 and the Mas receptor gene treatment-to-control ratios. The most prominent differences between BHR and SHR were observed in SOD1 and Mas receptor expressions, with large effects of opposite sign in BHR versus SHR. Our data indicate that an increase of NO release activates signaling in the renal cortex of pre-hypertensive rats after pioglitazone treatment. Improvement of NO availability, AT2R, Mas receptors and aberrant redox regulation is thought to be the major correlated mechanisms mediating the BP decrease affected by the PPARγ agonist treatment. We also observed that the most sensitive tissue responses to PPARγ-dependent activation of Nrf2 have been primarily found in the kidney of young hypertensive animals.

Expediency of application of animals with the spontaneous hypertensia for modelling of the metabolic syndrome

When used within 11 weeks of diet “cafeteria diet” in spontaneously-hypertensive animals could lead to an increase in systolic blood pressure by 9%, sustained hyperglycemia, increased blood concentrations of triglycerides and cholesterol, as well as an increase in the relative content of visceral fat. In normotensive animals line Wistar-Kyoto prolonged use of “cafeteria diet” was accompanied only by an increase in blood glucose, cholesterol and triglycerides. Thus, the spontaneously hypertensive animals, the application of high-calorie diet demonstrated by three criteria pathogenesis of the metabolic syndrome: hyperglycemia, hypertension and visceral obesity, which allows you to use the model for the study of drugs aimed at treatment of metabolic syndrome.

Dendritic morphology of neurons in medial prefrontal cortex, hippocampus, and nucleus accumbens in adult SH rats

We have studied, in spontaneously hypertensive (SH) rats at different ages (2, 4, and 8 months old), the dendritic morphological changes of the pyramidal neurons of the medial prefrontal cortex (mPFC) and hippocampus and medium spiny neurons of the nucleus accumbens (NAcc) induced by the chronic effect of high-blood pressure. As control animals, we used Wistar-Kioto (WK) rats. Blood pressure was measured every 2 months to confirm the increase in arterial blood pressure. Spontaneous locomotor activity was assessed, and then brains were removed to study the dendritic morphology by the Golgi-Cox stain method followed by Sholl analysis. SH animals at 4 and 8 months of age showed decreased spine density in pyramidal neurons from the mPFC and in medium spiny cells from the NAcc. At 8 months of age as well the pyramidal neurons from the hippocampus exhibited a reduction in the number of dendritic spines. An increase in locomotion in a novel environment at all ages in the SH rats was observed. Our results indicate that high-blood pressure alters the neuronal dendrite morphology of the mPFC, hippocampus, and NAcc. The increased locomotion behavior supports the idea that dopaminergic transmission is altered in the SH rats. This could enhance our understanding of the consequences of chronic high-blood pressure on brain structure, which may implicate cognitive impairment in hypertensive patients.

Cardiopulmonary responses in spontaneously hypertensive and Wistar-Kyoto rats exposed to concentrated ambient particles from Detroit, Michigan

Toxicological effects have been observed in rats exposed to concentrated ambient particles (CAPs) from different regions of the United States. The objective of this study was to evaluate the cardiopulmonary and systemic effects of CAPs in Detroit. The authors stationed a mobile concentrator at a location near major traffic and industrial sources. Spontaneously hypertensive (SH) and Wistar-Kyoto (WKY) rats were exposed to fine CAPs (diameter < 0.1–2.5 μm) 8 h/day for 13 consecutive days. Animals were implanted with telemeters, and electrocardiogram data were recorded continuously. Bronchoalveolar lavage (BAL) fluid and plasma were analyzed. Comprehensive exposure monitoring was conducted, including CAPs components. CAPs exposure concentrations were 103–918 μg/m3 (mean = 502 μg/m3). The authors found no statistically significant differences in heart rate or SDNN (standard deviation of the normal-to-normal intervals), a measure of heart rate variability, between CAPs-exposed and control rats. The authors found significantly higher levels of C-reactive protein in the serum of CAPs-exposed SH rats compared with air-exposed animals. Protein in BAL fluid was elevated in WKY rats exposed to CAPs. Measurement of trace metals in lung tissue showed elevated concentrations of V, Sb, La, and Ce in CAPs-exposed SH animals versus controls. These elements are generally associated with oil combustion, oil refining, waste incineration, and traffic. Examination of wind rose data from the exposure period confirmed that the predominant wind direction was SSW, the direction of many of the aforementioned sources. These results indicate that ambient particles in Detroit can cause mild pulmonary and systemic changes in rats, and suggest the importance of local PM2.5 sources in these effects.

Effects of Acute Stress on Blood Pressure, Catecholamines, and Renal Interlobar Artery Constriction in Spontaneously Hypertensive (SHR) and Normotensive (WKY) Male Rats

Human cardiovascular diseases are often preceded by and exaggerated with stress, affecting blood pressure, catecholamines (CATS), and vessel reactivity. To investigate these mechanisms we used acute restraint stress and measured changes in: systolic blood pressure (SBP), plasma and urinary CATS, and responses of isolated renal interlobar arteries to the vasoconstrictor phenylephrine (PE). We hypothesized that stress would increase sympathetic nervous system (SNS) response by elevating SBP, both plasma and urinary CATS, and increase constriction of renal interlobar arteries. Adult male SHR rats were subjected to 4 weeks of 1hr restraint stress (n=8, 3dys/wk) compared to non‐stressed SHR (n=6) and WKY (n=6) controls. Data pending for stressed WKY males. Blood pressure was measured weekly via tail cuff, and CATS were assayed by HPLC. Small renal interlobar artery constriction of response to PE was determined using a pressurized arteriograph system. Stressed SHR animals exhibited increased plasma and urinary CATS. Constrictor responses to PE in stressed animals were decreased when compared to control animals, for example at 1.0mmol PE stressed SHRs demonstrated 48% maximum constriction while controls showed 80.3% (SHR) and 75.3% (WKY). In conclusion, acute stress does increase SNS activity through plasma CATS, but did not increase SBP. Vasoconstrictor responses of isolated arteries appear to be increased.

Microvascular Network Restructuring Associated with MMP Inhibition in Spontaneously Hypertensive Rats

Recently, we have shown that MMP inhibition via doxcycyline treatment normalizes blood pressure and attenuates cell dysfunction, i.e. insulin resistance, in adult spontaneously hypertensive (SHR) rats. The objective of this work was to determine whether MMP inhibition leading to blood pressure normalization in hypertensive animals is associated with microvascular network structural alterations. Age matched (14–16 wks) SHR and Wistar‐Kyoto (WKY) rats were administered normal drinking water with and without doxycycline (5.4 mg/kg/d) for 12 weeks. Mesenteric tissues were harvested from 3–5 animals per experimental group and immunolabeled for CD31. Intact microvascular networks were compared based on 3 metrics: vascular area per total tissue area, vessel length per vascular area, and capillary sprouts (blind ended vessels) per vascular area. Microvascular networks from control SHR animals exhibited decreased vascular area per tissue area (P=0.030) and increased vessel length per vascular area (P=0.039) compared to the control WKY group. Networks from the doxycycline treated‐SHR group did not exhibit similar differences. Additionally, doxycylcline treatment served to decrease capillary sprouting per vascular area in SHR animals (P=0.039). These results suggest that microvascular network patterning is linked to MMP activity in adult spontaneously hypertensive rats. Supported by NIH‐HL10881.

Pharmacokinetic-pharmacodynamic (PK-PD) modeling of cardiovascular effects of metoprolol in spontaneously hypertensive rats: a microdialysis study

The present work addressed possible alterations in the pharmacokinetics and the in vivo pharmacodynamic of metoprolol (MET) in spontaneously hypertensive (SH) rats and Wistar Kyoto (WKY) animals by means of the microdialysis technique. The correlation between MET unbound plasma concentrations and its pharmacological effects, such as heart rate and blood pressure change, was also examined in SH and WKY rats by the application of a PK-PD model. MET dialysate concentrations and its chronotropic and blood pressure effect were determined during 3 h after the administration of 3 and 10 mg.kg(-1) of the drug. A PK-PD model with a separate effect compartment was used to analyse the data. A good correlation between plasma MET concentrations and its hypotensive and chronotropic effect was found in all experimental groups. Although a greater maximal effect (E(max)) for the antihypertensive effect of MET was observed in SH rats (WKY: E(max): -17+/-1 mmHg; SH: E(max): -28+/-4 mmHg; P<0.05 versus WKY rats), no differences were found in the concentration yielding half-maximal response (IC(50)) comparing SH (IC(50): 583+/-146 ng x ml(-1)) and WKY animals (IC(50): 639+/-187 ng x ml(-1)). The bradycardic effect of MET was greater in SH rats (E(max): -29+/-1%, P<0.05 versus WKY rats) than in WK animals (E(max): -22+/-2%), but no differences were observed in the IC(50) comparing both experimental groups (WKY: IC(50): 187+/-53 ng x ml(-1); SH: IC(50): 216+/-62 ng x ml(-1)). Pharmacokinetic analysis shows that the volume of distribution of MET was greater in SH rats (Vd: 3.4+/-0.5 l, P<0.05 versus WKY rats) with regard to Wistar Kyoto (WKY) animals (Vd: 1.9+/-0.2 l). The results suggest that the pharmacokinetic behaviour of metoprolol are modified in SH rats, resulting in an increased volume of distribution. A greater maximal efficacy to the hypotensive effect of metoprolol was observed in SH rats, suggesting participation of beta-adrenoceptors in the maintenance of the hypertension. Also, a greater chronotropic response to metoprolol was found in the hypertensive group compared with WKY animals, suggesting that, at least in part, the greater cardiac effect of metoprolol explained the enhanced hypotensive response of the beta blocker in the SH animals.

Hypothalamic cardiovascular effects of angiotensin-(1–7) in spontaneously hypertensive rats

The objective of the present work was to study the cardiovascular actions of the intrahypothalamic injection of Ang-(1–7) and its effects on the pressor response to Ang II in spontaneously hypertensive (SH) rats and Wistar Kyoto (WKY) animals. In anaesthetized SH and WKY rats, a carotid artery was cannulated for mean arterial pressure (MAP) measurement and a stainless-steel needle was inserted into the anterior hypothalamus for drug administration. The cardiovascular effects of the intrahypothalamic administration of Ang-(1–7) were determined in SH and WKY rats. In SH rats, the effect of irbesartan and d-Ala-Ang-(1–7) on Ang-(1–7) cardiovascular effect was also evaluated. Ang II was administered in the hypothalamus of SH and WKY rats and changes in blood pressure and heart rate were measured followed by the administration of Ang II, Ang II + Ang-(1–7) or Ang II + d-Ala-Ang-(1–7). Ang-(1–7) did not the change basal MAP in WKY rats, but induced a pressor response in SH animals. Whilst the co-administration of d-Ala-Ang-(1–7) did not affect the response to Ang-(1–7), the previous administration of irbesartan prevented the effect of the peptide. The intrahypothalamic injection of Ang II induced a significantly greater pressor response in SH animals compared to normotensive rats. The co-administration of Ang-(1–7) with Ang II did not affect the pressor response to Ang II in the WKY group. In SH rats, whilst the co-administration of Ang-(1–7) with Ang II reduced the pressor response to Ang II, the concomitant application of d-Ala-Ang-(1–7) with Ang II increased the pressor response to the octapeptide after 5 and 10 min of intrahypothalamic administration. In conclusion, our result demonstrated that the biologically active peptide Ang-(1–7) did not participate in the hypothalamic blood pressure regulation of WKY animals. In SH rats, Ang-(1–7) exerted pleiotropic effects on blood pressure regulation. High dose of the heptapeptide produced a pressor response because of an unspecific action by activation of AT 1 receptors. The concomitant administration of lower doses of Ang-(1–7) with Ang II reduced the pressor response to the octapeptide. Finally, the effect of AT 1–7 antagonist on Ang II pressor response suggested that hypothalamic formed Ang-(1–7) are implicated in the regulation of the cardiovascular effects of Ang II.

Strain-dependent response to cerebral ischemic preconditioning: differences between spontaneously hypertensive and stroke prone spontaneously hypertensive rats

Ischemic preconditioning (PC) is a phenomenon whereby a brief exposure to ischemia renders a tissue more tolerant to a subsequent sustained ischemic insult. Animals of the Spontaneously Hypertensive (SHR) and the Spontaneously Hypertensive Stroke-Prone (SHR-SP) rat strains produce cerebral infarcts that are larger and more reproducible in size than infarcts of normotensive rats. This study compared the effects of PC in SHR and SHR-SP rats, under the hypothesis that PC may not be as effective in the SHR-SP, a strain genetically predisposed to stroke. There were two groups per strain, with between eight and ten animals each. The Precondition group (PC) had a 10 min occlusion of the middle cerebral artery on day −1. On the same day the Sham group (Sham) received sham surgery. On day 0, both groups underwent permanent occlusion of the middle cerebral artery. The ischemic lesion was measured on day 1 using T 2-weighted magnetic resonance imaging. Percent hemispheric infarct was significantly reduced in SHR PC vs. SHR Sham, SHR-SP PC vs. SHR-SP Sham, and SHR PC vs. SHR-SP PC. Thus, rats of the SHR-SP strain respond to PC less markedly than SHR animals. Both models may now be used to elucidate the mechanisms underlying PC.

Estudo do efeito da amiodarona sobre o peso corpóreo e sobre determinantes morfológicos e citopatológicos do pulmão em ratos machos e fêmeas das linhagens Wistar, Wistar-Kyoto e SHR

Introdução: A maioria dos estudos experimentais sobre a toxicidade pulmonar induzida por amiodarona tem sido realizada em ratos machos da linhagem Fischer-344. Objetivos: Investigar o efeito da amiodarona sobre o peso corpóreo e sobre determinantes morfológicos e citopatológicos do pulmão em outras linhagens de ratos de ambos os sexos. Métodos: Grupos de ratos machos e de fêmeas das linhagens Wistar, Wistar-Kyoto (WKY) e espontaneamente hipertenso (SHR) receberam, por gavagem, durante quatro semanas, 175mg/kg/dia de amiodarona em suspensão salina. Os grupos controles receberam apenas salina. Foram estudados ganho de peso corpóreo, celularidade total e diferencial do lavado broncoalveolar (LBA) e histopatologia dos pulmões. Resultados: Mortalidade pela amiodarona foi observada nos ratos WKY tratados, sendo maior em machos. Animais SHR tratados de ambos os sexos apresentaram o menor ganho de peso entre as linhagens estudadas. Ratos machos Wistar e SHR tratados apresentaram maior ganho de peso do que as fêmeas das suas respectivas linhagens. O LBA de ratos SHR tratados de ambos os sexos era hemorrágico. A celularidade do LBA foi maior em machos tratados (WKY &gt; Wistar &gt; SHR). Entretanto, nos machos e fêmeas WKY a contagem diferencial mostrou o menor percentual de macrófagos e o maior de neutrófilos entre as três linhagens. Macrófagos do LBA de ratos Wistar tratados apresentavam fosfolipidose, enquanto a maioria dos macrófagos de ratos SHR tratados eram normais. No exame anatomopatológico dos pulmões, não houve diferenças entre os sexos e não foi observada pneumonite. Em ratos Wistar o exame foi caracterizado pela acentuada quantidade de macrófagos "espumosos" intra-alveolares, em ratos WKY, por inúmeros abscessos intraparenquimatosos e em ratos SHR, pela hemorragia alveolar. Conclusões: 1) a amiodarona induz em ratos Wistar maior quantidade de macrófagos espumosos do que nas linhagens WKY e SHR, embora no modelo utilizado eles não desenvolvam pneumonite; 2) a amiodarona tem maior efeito sobre os determinantes morfológicos e citopatológicos do pulmão em animais do sexo masculino.

Abrogated leptin-induced cardiac contractile response in ventricular myocytes under spontaneous hypertension: role of Jak/STAT pathway.

Leptin regulates cardiovascular function. Leptin levels are elevated in obesity and hypertension and may play a role in cardiovascular dysfunctions in these comorbidities. This study was designed to determine the influence of hypertension on the cardiac contractile response of leptin. Mechanical and intracellular Ca(2+) properties were evaluated using an IonOptix system in ventricular myocytes from spontaneously hypertensive (SHR) and age-matched Wistar Kyoto (WKY) rats. The contractile properties included peak shortening (PS), duration and maximal velocity of shortening/relengthening (TPS/TR(90), +/-dL/dt), and fura-fluorescence intensity change (DeltaFFI). NO and nitric oxide synthase (NOS) activity were assessed by the Griess and the (3)H-arginine/citrulline conversion assays, respectively. The leptin receptor (Ob-R) and the Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway were evaluated by Western blot analysis. SHR animals displayed significantly elevated blood pressure and plasma leptin levels. Leptin elicited a concentration-dependent inhibition of PS and DeltaFFI in WKY, but not in SHR myocytes. Leptin did not affect TPS, TR(90), or +/- dL/dt. The difference in leptin-induced contractile response between the WKY and the SHR groups was abolished by the NOS inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME), but not by elevated extracellular Ca(2+). Either the JAK2 inhibitor AG-490 or the mitogen-activated protein (MAP) kinase inhibitor SB203580 abrogated the leptin-induced response in the WKY myocytes, whereas AG-490 unmasked a negative response in PS in the SHR myocytes. SHR myocytes displayed similar Ob-R protein abundance and basal NO levels, a blunted leptin-induced increase in NOS activity as well as enhanced basal STAT3 levels compared with the WKY group. These data indicate that the leptin-induced cardiac contractile response is abolished by spontaneous hypertension, possibly because of mechanisms involving altered JAK/STAT, MAP kinase signaling, and NO response.

Antihypertensive drug therapy and antioxidant enzyme mRNA levels in spontaneously hypertensive (SHR) rats

Previous studies have shown that chronic treatment of SHR (spontaneously hypertensive) rats with the antihypertensive drugs captopril, hydralazine and terazosin results in changes in the specific activities of the antioxidant enzymes glutathione peroxidase, catalase and Cu/Zn superoxide dismutase in liver and myocardium. In order to determine if these changes were caused by alterations in the levels of the mRNAs for these enzymes, the tissue levels of the antioxidant enzyme mRNAs have been measured. In myocardium, all three drug treatments increased Cu/Zn superoxide dismutase mRNA but decreased glutathione peroxidase mRNA levels, and in liver, all three drugs changed glutathione peroxidase mRNA levels. In comparison to untreated SHR animals, the levels of all three mRNAs were altered in the myocardium, but not in the liver, of normotensive WKY rats. Comparisons of mRNA levels with tissue enzyme specific activities suggest that tissue antioxidant enzyme expression is, in most cases, regulated by antihypertensive drugs through transcriptional control mechanisms.

Interaction of diabetes and hypertension on determinants of endothelial adhesiveness.

Epidemiological studies have established that diabetes mellitus and hypertension are independent risk factors for atherosclerosis. One of the earliest abnormalities seen in atherogenesis is enhanced monocyte adherence to the endothelium. The mechanisms by which diabetes mellitus or hypertension enhances monocyte-endothelial cell interactions are incompletely characterized. It is not known whether there are additive interactions between these risk factors on endothelial adhesiveness for monocytes. Male Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats were fed a normal or fructose-enriched diet. In some cases, animals were injected with streptozotocin (35 mg/kg body weight) to induce diabetes. After 2 weeks, plasma was drawn for biochemical measurements, and thoracic aortas were harvested, opened longitudinally, and exposed to fluorescently labeled mouse monocytoid cells (WEHI 78/24, 2 x 10(6)/mL) for 30 minutes on a rocking platform. Adherent cells were counted by epifluorescence microscopy. WEHI 78/24 binding to aortic segments from SHR animals was elevated compared with segments from WKYs. Fructose feeding alone had no effect on endothelial adhesiveness. When WKYs were made hyperglycemic by STZ injection, monocyte binding was 160% of the control value. Elevated monocyte binding was also observed in aortas derived from SHR animals injected with STZ, indicating an additive effect of hypertension and hyperglycemia. To determine whether alterations in oxidative state played a role in the endothelial adhesiveness, aortic segments were exposed to lucigenin (250 micromol/L) for measurement of superoxide anion. Aortic segments from SHR elaborated 120% more superoxide anion than did controls. Elevated free-radical production was also observed in aortas from diabetic WKYs. Furthermore, thoracic aortas derived from diabetic SHR animals elaborated more superoxide anion than did any of the other groups (374%, P<0.05). Immunohistochemical staining for monocyte chemotactic protein-1 demonstrated increased expression in aortas isolated from diabetic WKY and SHR compared with control vessels. These studies demonstrate that both diabetes and hypertension lead to increased monocyte adherence to the endothelium. This abnormality is associated with increased vascular superoxide production and monocyte chemotactic protein-1 expression. Furthermore, there appears to be an additive interaction between hyperglycemia and hypertension in their effects on endothelial adhesiveness and its determinants.

Age-dependent Modifications of the Role of Prostanoids in Cardiac Preparations from Normotensive and Hypertensive Rats

The cardiac response to field stimulation of adrenergic nerve terminals in isolated atrial preparations from adult (6-month-old) normotensive Wistar Kyoto (WKY) and spontaneously hypertensive (SH) rats was enhanced in comparison to that observed in the atrial tissue of young (2-month-old) animals of both strains; the increase in the sympathetic response was significantly higher in preparations from SHR than in those from age-matched WKY rats. The sensitivity of cardiac adrenergic neurotransmission to the prejunctional inhibitory effects exerted by exogenously administered prostaglandin E 2 (0.1 nM-1 μM) and iloprost (0.1-10 μM) did not show any strain-dependent difference in preparations from both young and adult rats. Moreover, acetylsalicylic acid (500 μM) induced a similar degree of potentiation of the response to sympathetic stimulation in atrial tissues of young WKY and SH animals; however, the effect of the cyclo-oxygenase inhibitor was completely missing in preparations from adult rats of both strains. Finally, arachidonic acid (10 μM) inhibited the adrenergic response to a greater extent in preparations from young and adult SH rats than in those from agematched normotensive rats. The results of the study indicate that, at least in cardiac preparations, changes in the modulatory role of endogenous prostaglandins occur as age-dependent processes and, therefore, may not be indicative of possible differences in the role of prostaglandins between hypertensive and normotensive animals. The possible significance of the dissimilar response to arachidonic acid, detected as the only difference between preparations from SH and WKY rats, is discussed.

Effect of casein, casein phosphopeptides and calcium intake on ileal 45Ca disappearance and temporal systolic blood pressure in spontaneously hypertensive rats.

Paracellular 45Ca absorption and temporal systolic blood pressure (SBP) measurements were recorded in spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats fed on casein (C) and soya-bean-protein isolate (S) diets, containing 20 (H), 5 (H) and 0.5 (L) g Ca/kg. Similar measurements were also taken in SHR rats only fed on C-M and S-M diets supplemented with 30 g caseinophosphopeptides (CPP)/kg. Absorption of 45Ca from the ileal loop was equivalent in both SHR and WKY animals and largely affected by the level of dietary Ca. In addition, animals fed on C diets exhibited significantly (P < 0.05) greater ileal absorption of 45Ca compared with S-fed animals. This result was attributed to the presence of CPP and a greater (P < 0.05) proportion of soluble 45Ca in the contents of the ileum. Animals fed on S diets supplemented with CPP confirmed this finding. The SBP of SHR rats was higher (P < 0.01) than WKY controls after 9-10 weeks of age. The temporal pattern of observed hypertension was independent of dietary influence in the SHR. The severity of hypertension in SHR rats was affected only by dietary Ca deficiency, and not by Ca supplementation or CPP enhancement of Ca bioavailability. These findings suggest that tryptic digestion products of casein in milk can enhance Ca bioavailability by increasing Ca solubility; however, this action had no effect in reducing hypertension in SHR.

Adult blood pressure reduction in spontaneously hypertensive rats reared by normotensive Sprague—Dawley mothers

Spontaneously hypertensive (SHR), Wistar-Kyoto (WKY) normotensive, and Sprague-Dawley (SD) normotensive rats were either reared by their natural mothers (controls) or fostered to a mother of one of the other strains. The effects of rearing environment were assessed by measures of body weight at weaning and adult resting mean arterial blood pressure (MAP) and heart rate (HR). At weaning, SHR control rats weighed less than WKY controls which in turn weighed less than SD controls. SHR and WKY rats reared by SD mothers weighed significantly more than their respective controls, whereas SD rats reared by either SHR or WKY mothers weighed less than SD control rats. Manipulation of the maternal environment was attended by a change in adult resting MAP in only one group. SHR rats reared by SD mothers had MAPs which were significantly lower than SHRs reared by their natural mothers. No within-strain adult HR differences were observed between control and cross-fostered groups. These data indicate that the effects of cross-fostering on adult resting MAP previously reported for SHR and WKY animals are generalizable to another normotensive strain. That is, genetically hypertensive (SHR) animals exposed to a normotensive (WKY or SD) maternal environment display a reduction in adult resting MAP, whereas hypertension or an increase in adult MAP is not induced in normotensive rats (WKY or SD) as a consequence of exposure to a hypertensive maternal environment.

Experimental intracerebral haemorrhage in normotensive and spontaneously hypertensive rats

Early changes in intracranial pressure (ICP) and mean arterial blood pressure (MABP) were studied in normotensive and spontaneously hypertensive (SHR) Wistar rats after the development of an experimental intracerebral haemorrhage (ICH). The volume of the ICH was 200 or 400 microliters and they were located in the nucleus caudatus or the subcortical area of the occipital lobe. Our study shows that 200 microliters ICH produced both in normotensive and SHR rats similar mortality rates and ICP changes. However, 400 microliters ICH lead to a significantly higher mortality in SHR rats. The systemic hypertensive response to the increasing of ICP was not observed in SHR animals. Thus, the increase in the cerebral pressure perfusion measured in normal rats does not happen in SHR rats. The cause of this fact in SHR rats could be due to local factors or related to alterations in the peripheral part of the vasomotor reflex.