Glial fibrillary acidic protein (GFAP) immunoreactivity correlates with cortical perfusion parameters determined by bolus tracking arterial spin labelling (bt-ASL) magnetic resonance (MR) imaging in the Wistar Kyoto rat.

Alterations in astrocyte number and function have been implicated in the pathophysiology of a number of psychiatric disorders. The development of magnetic resonance imaging (MRI) as a tool in the animal laboratory has enabled an investigation of the relationship between pathological and neuroimaging markers in animal models. However the physiological processes which underlie these markers and their role in mediating behavioural deficits is still poorly understood. Rodent models have provided us with important insights into physiological and cellular mechanisms which may mediate anxiety and depression-related behaviours. The Wistar-Kyoto (WKY) rat is a strain which endogenously expresses highly anxious and depressive-like behaviours and has previously been reported to exhibit alterations in immunoreactivity for the astrocytic marker glial fibrillary acidic protein (GFAP) in brain sub-regions relative to more stress resilient out-bred strains. Here we report that the depressive and anxiety-like behaviours exhibited by the WKY rat strain are associated with alterations in brain morphology including a decrease in hippocampal volume, coupled with reduced resting state frontal cortical perfusion as assessed by MR bolus tracking arterial spin labelling (bt-ASL) relative to the out-bred Wistar strain. Pre-limbic cortical GFAP immunoreactivity and astrocyte cell number were positively correlated with cortical blood perfusion in the WKY strain. These experiments provide a link between pathological and neuroimaging markers of aberrant astrocytic function and add validity to the WKY rat as a model for co-morbid anxiety and depression.

Repeated forced swim stress differentially affects formalin-evoked nociceptive behaviour and the endocannabinoid system in stress normo-responsive and stress hyper-responsive rat strains.

Repeated exposure to a homotypic stressor such as forced swimming enhances nociceptive responding in rats. However, the influence of genetic background on this stress-induced hyperalgesia is poorly understood. The aim of the present study was to compare the effects of repeated forced swim stress on nociceptive responding in Sprague-Dawley (SD) rats versus the Wistar Kyoto (WKY) rat strain, a genetic background that is susceptible to stress, negative affect and hyperalgesia. Given the well-documented role of the endocannabinoid system in stress and pain, we investigated associated alterations in endocannabinoid signalling in the dorsal horn of the spinal cord and amygdala. In SD rats, repeated forced swim stress for 10 days was associated with enhanced late phase formalin-evoked nociceptive behaviour, compared with naive, non-stressed SD controls. In contrast, WKY rats exposed to 10 days of swim stress displayed reduced late phase formalin-evoked nociceptive behaviour. Swim stress increased levels of monoacylglycerol lipase (MAGL) mRNA in the ipsilateral side of the dorsal spinal cord of SD rats, an effect not observed in WKY rats. In the amygdala, swim stress reduced anandamide (AEA) levels in the contralateral amygdala of SD rats, but not WKY rats. Additional within-strain differences in levels of CB1 receptor and fatty acid amide hydrolase (FAAH) mRNA and levels of 2-arachidonylglycerol (2-AG) were observed between the ipsilateral and contralateral sides of the dorsal horn and/or amygdala. These data indicate that the effects of repeated stress on inflammatory pain-related behaviour are different in two rat strains that differ with respect to stress responsivity and affective state and implicate the endocannabinoid system in the spinal cord and amygdala in these differences.

Brown Norway rats, a putative schizophrenia model, show increased electroencephalographic activity at rest and decreased event-related potential amplitude, power, and coherence in the auditory sensory gating paradigm.

In recent schizophrenia clinical research, electroencephalographic (EEG) oscillatory activities induced by a sensory stimulus or behavioral tasks have gained considerable interest as functional and pathophysiological biomarkers. The Brown Norway (BN) rat is a putative schizophrenia model that shows naturally low sensorimotor gating and deficits in cognitive performance, although other phenotypes have not been studied. The present study aimed to investigate the neurophysiological features of BN rats, particularly EEG/event-related potential (ERP). EEG activity was recorded at rest and during the auditory sensory gating paradigm under an awake, freely moving condition. Frequency and ERP analysis were performed along with time-frequency analysis of evoked power and intertrial coherence. Compared with Wistar-Kyoto rats, a well-documented control line, BN rats showed increased EEG power at rest, particularly in the theta and gamma ranges. In ERP analysis, BN rats showed reduced N40-P20 amplitude but normal sensory gating. The rats also showed reduced evoked power and intertrial coherence against auditory stimuli. These results suggest that BN rats show features of EEG/ERP measures clinically relevant to schizophrenia and may provide additional opportunities for translational research.

Comparison of the validity of the use of the spontaneously hypertensive rat as a model of attention deficit hyperactivity disorder in males and females.

The spontaneously hypertensive rat (SHR) is a commonly used and well-studied rodent model of attention deficit hyperactivity disorder (ADHD). Sex differences in the cognitive symptoms of ADHD are reported. However, the female SHR rat is much less studied than its male counterpart. The goal of the current study was to assess the validity of the SHR rodent model of ADHD by examining attentional performance, inhibitory control, and hyperactivity in both male and female SHR rats. Adult SHR and control Wistar-Kyoto rats were trained on the 5-choice serial reaction time task, a self-paced test of attention and inhibitory control. This task requires animals to identify the location of a brief light stimulus among five possible locations under several challenging conditions. Analyses of percent correct revealed that attentional performance in SHR females was not significantly different from control females, whereas attentional performance in SHR males was significantly different from control males. Analyses of the number of premature responses revealed that SHR rats made more inhibitory control errors than did control rats and that this decrease in inhibitory control was present in both SHR males and females. Analyses of activity in the open field revealed that SHR rats were more hyperactive than were control rats and that this increased hyperactivity was present in both SHR males and females. The current findings have implications for the study of sex differences in ADHD and for the use of SHR rats as a model of ADHD in females.

Differences in striatal spiny neuron action potentials between the spontaneously hypertensive and Wistar-Kyoto rat strains.

The spontaneously hypertensive rat (SHR) and the Wistar-Kyoto (WKY) inbred rat strains display behavioral differences characterized by relative increases and decreases in levels of activity. Both strains have subsequently been utilized as animal models of hyperactive and hypoactive behavioral traits. The etiology of these behavioral characteristics is poorly understood, but may stem from alterations in the physiology of selected neural circuits or catecholamine systems. This study investigated the cellular properties of neurons from three genetically related strains: the SHR; WKY; and Wistar (WI). In vivo intracellular recordings were made under urethane anesthesia from spiny projection neurons in the striatum, a brain area involved in behavioral activation. Results obtained from 71 spiny projection neurons indicate that most cellular properties of these neurons were very similar across the three strains. However, the amplitude and half-duration of both spontaneously occurring and current-evoked action potentials were found to be significantly different between the SHR and WKY strains with neurons from the SHR firing action potentials of relatively greater amplitude and shorter duration. Action potential parameters measured from the WI rats were intermediate between the two other strains. These differences in action potentials between two behaviorally distinct strains may reflect altered functioning of particular membrane conductances.

Wistar Kyoto rats have impaired gastric accommodation compared to Sprague Dawley rats due to increased gastric vagal cholinergic tone.

OBJECTIVE: Gastric balloon distension shows that, in comparison with Sprague Dawley (SD) rats, Wistar Kyoto (WKY) rats have a decreased volume response owing to a lower accommodation rate. The aim of this study was to compare the role of the vagal cholinergic and nitrergic pathways in the accommodation reflex in these rat strains. MATERIAL AND METHODS: The volume response to ramp-tonic gastric balloon distension was pharmacologically manipulated by using L-NAME 25 mg/kg i.v., molsidomine 20 mg/kg i.p., atropine 1 mg/kg i.v. and clonidine 0.7 mg/kg s.c. RESULTS: Following L-NAME, the maximal volume response to distension was significantly decreased in WKY rats (0.74+/-0.11 ml versus 1.18+/-0.13 ml) whereas only a tendency to such a decrease was seen in SD rats. The NO donor molsidomine significantly increased the volume in SD rats (4.91+/-0.46 ml versus 1.81+/-0.50 ml) but only weakly in WKY rats. Atropine significantly increased the gastric volume in WKY rats (2.78+/-0.29 ml versus 1.00+/-0.17 ml) but not in SD rats. Clonidine increased the accommodation rate in the WKY rat, resulting in increased maximal volume (1.69+/-0.26 ml versus 0.65+/-0.11 ml) indicating a reduction in acetylcholine release as a consequence of stimulated presynaptic adrenergic receptors on cholinergic neurons. CONCLUSIONS: The results indicate that WKY rats may have an increased gastric vagal cholinergic drive, which, during distension, masks the relaxing effect of NO-releasing neurons. The findings in WKY rats could be of relevance for functional dyspeptic patients with impaired gastric accommodation to meals.

Antidepressant drug induced alterations in binding to central dopamine transporter sites in the Wistar Kyoto rat strain.

The Wistar Kyoto (WKY) rat has been proposed as an animal model of depressive behavior. Exposing WKY rats to stress stimulation produces symptoms such as anhedonia, psychomotor retardation, ambivalence and negative memory bias. Given the role of the mesolimbic dopamine (DA) system in cognitive, emotional and motivational behaviors, we previously examined the distribution of DA transporter (DAT) sites in the brains of WKY compared to Wistar (WIS) and Sprague-Dawley (S-D) rats. WKY rats exhibited significant differences in DAT binding sites in the cell body as well as mesolimbic areas compared to the other strains. It was reasoned that these differences may lead to altered synaptic levels of DA in specific brain regions thus contributing to the behavioral differences observed in this rat strain. Thus, the present study examined whether repeated treatment with antidepressant drugs that block the uptake of DA (nomifensine and bupropion) would modify [3H]-GBR12935 binding to DAT sites in WKY rats compared to WIS and S-D rats. The results indicate that while nomifensine and bupropion increased the binding of [3H]-GBR12935 to DAT sites in the mesocorticolimbic regions in WKY rats, these drugs increased the binding of [3H]-GBR12935 to DAT sites in the cell body areas in WIS rats but not in S-D and WKY rats. The data from this study suggest that antidepressant induced alterations in DAT sites in the mesocorticolimbic brain regions may play a role in the behavioral improvement seen in WKY rats, as measured by the Open Field Test (OFT) and the Porsolt Forced Swim Test (FST).

Rat strain effects of AT1 receptor activation on D1 dopamine receptors in immortalized renal proximal tubule cells.

The dopaminergic and renin-angiotensin systems regulate blood pressure, in part, by affecting sodium transport in renal proximal tubules (RPTs). We have reported that activation of a D1-like receptor decreases AT1 receptor expression in the mouse kidney and in immortalized RPT cells from Wistar-Kyoto (WKY) rats. The current studies were designed to test the hypothesis that activation of the AT1 receptor can also regulate the D1 receptor in RPT cells, and this regulation is aberrant in spontaneously hypertensive rats (SHRs). Long-term (24 hours) stimulation of RPT cells with angiotensin II, via AT1 receptors increased total cellular D1 receptor protein in a time- and concentration-dependent manner in WKY but not in SHR cells. Short-term stimulation (15 minutes) with angiotensin II did not affect total cellular D1 receptor protein in either rat strain. However, in the short-term experiments, angiotensin II decreased cell surface membrane D1 receptor protein in WKY but not in SHR cells. D1 and AT1 receptors colocalized (confocal microscopy) and their coimmunoprecipitation was greater in WKY than in SHRs. However, AT1/D1 receptor coimmunoprecipitation was decreased by angiotensin II (10(-8) M/24 hours) to a similar extent in WKY (-22+/-8%) and SHRs (-22+/-12%). In summary, these studies show that AT1 and D1 receptors interact differently in RPT cells from WKY and SHRs. It is possible that an angiotensin II-mediated increase in D1 receptors and dissociation of AT1 from D1 receptors serve to counter regulate the long-term action of angiotensin II in WKY rats; different effects are seen in SHRs.

Stimulus processing and associative learning in Wistar and WKHA rats.

This study assessed basic learning and attention abilities in Wistar-Kyoto hyperactive (WKHA) rats using appetitive conditioning preparations. Two measures of conditioned responding to a visual stimulus, orienting behavior (rearing on the hind legs), and food cup behavior (placing the head inside the recessed food cup) were measured. In Experiment 1, simple conditioning, but not extinction, was impaired in WKHA rats compared with Wistar rats. In Experiment 2, nonreinforced presentations of the visual cue preceded the conditioning sessions. WKHA rats displayed less orienting behavior than Wistar rats but comparable levels of food cup behavior. These data suggest that WKHA rats exhibit specific abnormalities in attentional processing as well as in learning stimulus-reward relationships.

The effects of chlorpyrifos on blood pressure and temperature regulation in spontaneously hypertensive rats.

Using radiotelemetry to monitor blood pressure and core temperature, studies in our laboratory have shown that a prolonged hypertensive response is elicited in rats exposed to chlorpyrifos, an organophosphate-based insecticide. Chlorpyrifos inhibits acetylcholinesterase activity, resulting in central and peripheral stimulation of central cholinergic pathways involved in blood pressure regulation. The spontaneously hypertensive rat has been shown to be more sensitive to central cholinergic stimulation. Therefore, we hypothesized that these rats would be more susceptible and sustain a greater hypertensive response when exposed to chlorpyrifos. Heart rate, cardiac contractility, core temperature, and blood pressure were monitored by radiotelemetry in SHRs and their Wistar Kyoto (WKY) normotensive controls following exposure to chlorpyrifos (10 mg/kg or 25 mg/kg, orally). Baseline blood pressure of SHRs was approximately 35 mmHg above that of WKYs prior to dosing. SHRs exhibited a greater and more sustained elevation in diastolic, mean and systolic blood pressure following exposure to 25 mg/kg of chlorpyrifos. The rise in blood pressure lasted for approximately 56 hours in SHRs compared to approximately 32 hours in WKYs. Chlorpyrifos also led to a prolonged elevation in daytime heart rate in both strains. There was a transient elevation in cardiac contractility in both strains lasting approximately 7 hr after exposure to chlorpyrifos. The hypothermic response to chlorpyrifos was similar in magnitude and duration for both strains. Plasma cholinesterase activity measured 4 hr after exposure to 25 mg/kg chlorpyrifos was inhibited to approximately 40% of control levels in both strains. Using the SHR strain as a model to study susceptible populations, the data suggest that individuals with a genetic predisposition to hypertension may be more susceptible from exposure to organophosphate-based insecticide, as manifested by an exacerbated hypertensive response.

A model of chronic heart failure in spontaneous hypertensive rats (SHR).

Common models of chronic heart failure (CHF) do not always result in parameters and symptoms that can be extrapolated to the clinical situation of patients with end-stage heart failure. The aim of this study was to establish and validate a new model of CHF in the rat. CHF was induced in Wistar Kyoto (WKY/NHsd) and spontaneously hypertensive (SHR/NHsd) rats by creating a permanent (8-week) occlusion of the left coronary artery 2 mm distal to the origin from the aorta by a modified technique. This resulted in a large infarction of the free left ventricular wall. The focus of attention was the validation of the geometric properties of the left ventricle and its contractility. The validation of the geometric properties of the left ventricle was done by a non-invasive magnetic resonance imaging (MRI) technique and by planimetry (stereology). Cardiodynamics (e.g. contractility) were evaluated in the isolated 'working heart' model. We were able to establish a new and predictive model of heart failure in the spontaneously hypertensive rat 8 weeks after coronary artery ligation. At this time point, the WKY rat did not show any symptoms of CHF. The model represents characteristic parameters and symptoms that can be extrapolated to the clinical situation of patients with end-stage heart failure (NYHA III-IV). Upon inspection, severe clinical symptoms of congestive heart failure were prominent, such as dyspnoea, subcutaneous oedema, pale-bluish limbs and impaired motion. Non-invasive sequential measurements by NMR techniques showed lung oedema, hydrothorax, large dilated left and right ventricular chambers and hypertrophy of the septum. The infarcted animals showed a reduced heart power, diminished contractility and enhanced heart work, much more so in the SHR/NHsd rat than in the WKY/NHsd rat. Furthermore the infarcted animals showed enhanced levels of hydroxyproline/proline ratios, again much more so in the SHR/NHsd rat than in the WKY/NHsd rat.

Chloride channel blockade attenuates the effect of angiotensin II on tubuloglomerular feedback in WKY but not spontaneously hypertensive rats.

Recent studies have shown that calcium-dependent chloride channels may play a crucial role in the modulation of the vascular effects of angiotensin II (ANG II). Thus, alterations in the function of these channels may be responsible for the enhanced renal vasoconstrictor and tubuloglomerular feedback (TGF) response to ANG II in spontaneously hypertensive rats (SHR). We investigated the effect of the calcium-dependent chloride channel blocker IAA-94 on renal hemodynamics and TGF responses. The renal interstitium was perfused with control solution, with ANG II, and with both ANG II and IAA-94. In Wistar Kyoto rats (WKY), perfusion with ANG II significantly increased renal vascular resistance (RVR), but the effect was significantly attenuated by perfusion with ANG II/IAA-94. In SHR, ANG II caused a significant elevation of RVR that was not altered by the simultaneous infusion of IAA-94. Proximal tubular stop flow pressure (P(sf)) was monitored during perfusion of peritubular capillaries with control solution, and subsequently with IAA-94, ANG II or both ANG II and IAA-94. TGF response magnitude of WKY rats was significantly augmented with ANG II, and this effect was suppressed by perfusion with ANG II /IAA-94. However, in SHR peritubular perfusion with ANG II/IAA-94 did not suppress the TGF response. We conclude that chloride channels susceptible to IAA-94 may play a significant role in modulating the effects of ANG II on renal hemodynamics, and that this modulation is absent in SHR.

Spontaneously hypertensive and Wistar Kyoto rats differ in delayed matching-to-place performance and response to dietary long-chain polyunsaturated fatty acids.

Spontaneously hypertensive rats (SHR) were used as an animal model of attention deficit hyperactivity disorder (ADHD). This study investigated whether, in comparison with its progenitor strain, Wistar-Kyoto rats (WKY), SHR would show deficits in spatial short-term memory in the delayed-matching-to-place (DMP) version of the Morris water maze and be more distracted by exposure to a novel stimulus during recall trials. It also addressed whether dietary supplementation with long-chain polyunsaturated fatty acids (LCPUFA) during development would increase brain docosahexaenoic acid (DHA) and improve SHR behavioral performance. Beginning at weaning (21 days), male SHR and WKY were fed either a control or LCPUFA supplemented diet [0.5% arachidonic acid (AA) and 0.9% DHA], and behavioral testing began at 8 weeks. The first three tasks comprised a series of problems, each consisting of an initial search trial and subsequent recall trials. The intertrial interval (ITI) between the search and recall trial was either 60 s or 60 min. Surprisingly, in contrast to SHR, WKY did not appear to use a spatial short-term memory strategy to solve the problem. Notwithstanding, the performance of both strains was affected by the delay, such that they showed longer path lengths at the long compared with the short ITI. There was no effect of dietary supplementation on DMP performance. SHR fed the control diet were less responsive to a novel stimulus introduced on the first recall trial than WKY, and this tended to increase with supplementation. Analysis of brain fatty acid composition indicated that supplementation did increase DHA in the phosphatidylethanolamine fraction in WKY; however, in SHR, there was either no change (phosphatidylethanolamine) or paradoxical decreases (phosphatidylcholine and phosphatidyserine/phosphatidylinositol). Further research is needed to determine whether SHR are an appropriate model for studying a possible relationship between dietary LCPUFA and the behavioral symptoms of ADHD.

Tyrosine hydroxylase gene expression in ventrolateral medulla oblongata of WKY and SHR: a quantitative real-time polymerase chain reaction study.

The aims of this study were, first, to determine quantitatively the levels of tyrosine hydroxylase (TH) gene expression in both peripheral and central sites related to blood pressure regulation, and to compare the level of expression in Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). Second, to see if any relationship exists between TH gene expression and systolic arterial blood pressure. Total RNA was isolated from adrenal glands and from tissue punches taken from the C1 and A1 cell groups in the rostral and caudal ventrolateral medulla oblongata of the brainstem, respectively. Total RNA was reverse-transcribed into cDNA followed by quantitative fluorescence detection polymerase chain reaction for TH cDNA. The levels of TH gene expression measured as a percentage of the house-keeping gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH), in SHR, were significantly higher ( approximately 2.5-fold) compared to WKY in all sites examined (P<0.01). There was a positive and significant relationship between systolic blood pressure and TH gene expression in the C1 area of the brainstem in both WKY (n = 5, P<0.05) and SHR (n=6, P<0.05). Taken together, these results suggest that elevated gene expression of the TH gene is associated with the phenotypic characteristic of SHR.

Tyrosine hydroxylase antisense gene therapy causes hypotensive effects in the spontaneously hypertensive rats.

We investigated the effect of antisense oligodeoxynucleotides (AS ODN) against tyrosine hydroxylase (TH) on hypertension and sympathetic nervous system activity in spontaneously hypertensive rats (SHR). Systolic blood pressure (SBP) in SHR treated with TH AS ODN (50, 200 microg/rat, i.v.) was significantly lower than that of control SHR. Epinephrine and norepinephrine levels, TH activity, and TH protein levels in the adrenal medulla of SHR were reduced concomitant with TH AS ODN treatment-induced changes in SBP. In contrast, TH AS ODN (200 microg/rat) had no effect on SBP in Wistar-Kyoto rats (WKY), despite significantly decreased catecholamine levels, TH activity, and TH protein levels. These findings suggest that peripheral systemic injection of TH AS ODN may be effective as hypotensive therapy in SHR.

Renomedullary interstitial cell lipid droplet content is increased in spontaneously hypertensive rats and by low salt diet.

OBJECTIVE: To compare the volumes of renomedullary interstitial cell (RMIC) lipid droplets (putative source of vasodepressor substance) in spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats on high and low salt diets as an indication of whether the renomedullary vasodepressor system of the SHR is defective. METHODS: Ten-week-old male SHR and WKY rats received a low (0.05% w/w) or high salt (5.0%) diet for 21 days. Conscious mean arterial pressure (MAP) was measured and the renal papilla perfusion fixed with a high osmolarity fixative. Using electron microscopic stereological techniques, the volume density of lipid in RMIC (VVLipid,RMIC) and the total volumes of lipid (VLipid) and RMIC (VRMIC) in papilla were measured. RESULTS: MAP of SHR (high 155 +/- 3 mmHg; low 151 +/- 3 mmHg) was significantly greater than WKY rats (high 126 +/- 2 mmHg; low 129 +/- 2 mmHg; P< 0.001), however salt diet had no significant effect on MAP. The VLipid of rats on the low salt diet was approximately 2.5 times greater than in rats on the high salt diet (P < 0.01). SHR had significantly greater VLipid than WKY rats irrespective of salt diet (P< 0.05; SHR-low 0.245 +/- 0.031 mm3, SHR-high 0.093 +/- 0.007 mm3; WKY-low 0.126 +/- 0.032 mm3, WKY-high 0.051 +/- 0.020 mm3). Similar differences were seen for VVLipid,RMIC, however VRMIC was not different between rat strains or salt diet groups. CONCLUSIONS: SHR and WKY rats responded similarly to the altered salt diets, and SHR demonstrated greater volumes of stored RMIC lipid droplets irrespective of the level of salt intake. These results indicate that SHR hypertension is not due to a deficiency in the amount of lipid droplets, the putative source of the renomedullary vasodepressor substance and that the renomedullary vasodepressor system of the SHR is capable of responding normally to the physiological stimulus of altered salt intake.

The effect of docarpamine, a dopamine pro-drug, on blood pressure and catecholamine levels in spontaneously hypertensive rats.

We studied the effects of bolus intravenous injection of the dopamine prodrug, docarpamine (200 microg/kg), on mean arterial pressure (MAP) and heart rate (HR) in Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHRs). In WKY rats (n=18), MAP and HR increased 5 min after docarpamine and then returned to baseline levels within 15 min. In contrast, in SHRs (n=15), MAP and HR gradually decreased, reaching a nadir 20 min after injection. Five min after docarpamine, plasma dopamine and 3,4-dihydroxy phenyl acetic (DOPAC) levels increased in both WKY rats (n=5) and SHRs (n=5). The docarpamine-induced changes in MAP and HR in both rat strains (n=5/strain) were blocked by the D1-like antagonist, SCH23390. alpha-Adrenergic (n=4) and vasopressin V1 (n=3) receptor blockade also abrogated the effects of docarpamine in WKY rats. We conclude that docarpamine differentially affects MAP and HR in WKY and SHRs. In SHRs, the depressor and bradycardiac effects of docarpamine are mediated by D1-like receptors. In WKY rats, the pressor and tachycardiac responses are caused by an interaction among D1-like, alpha-adrenergic, and V1 receptors.

Insulin-stimulated cardiac glucose uptake is impaired in spontaneously hypertensive rats: role of early steps of insulin signalling.

OBJECTIVE: Although the heart is one of the target organs of insulin, it is still unknown whether the effect of insulin on cardiac muscle is preserved in essential hypertension, where insulin resistance has been observed in skeletal muscle. METHODS: We evaluated cardiac glucose uptake and the early steps of insulin signalling in spontaneously hypertensive (SHR, 10-12 weeks old) and in age-matched normotensive Wistar-Kyoto (WKY) rats. Cardiac glucose uptake (micromol/100 g per min) was assessed by 2-[14C]deoxyglucose method. After an overnight fast, 16 WKY rats and 17 SHR underwent a hyperinsulinemic euglycemic clamp. In particular, 2-h intravenous (i.v.) infusion of insulin (10 mU/kg per min) or saline (NaCl 0.9%) was administered, followed by an i.v. bolus injection of 2-[14C]deoxyglucose (100 microCi/kg) to measure cardiac glucose uptake. RESULTS: During saline infusion, cardiac glucose uptake was significantly higher in SHR compared to WKY rats (85 +/- 18 versus 8 +/- 3 mg/kg per min, P < 0.01). Furthermore, insulin was able to markedly increase cardiac glucose uptake in WKY rats whereas this insulin action was entirely abolished in SHR; thus, the cardiac glucose uptake became similar in the two rat strains (76 +/- 16 versus 82 +/- 16 mg/kg per min, not significant). More importantly, during saline infusion SHR showed a significantly higher phosphorylation of insulin receptor substance-1 (IRS-1) coupled to enhanced association of the p85 subunit of phosphatidylinositol 3-kinase (PI 3-kinase) to IRS-1 and to an increased PI 3-kinase activity compared to WKY rats. As expected, insulin exposure evoked an activation of its signalling cascade in WKY rats. In contrast, in SHR, the hormone failed to activate post-receptor molecular events. CONCLUSIONS: Our data indicate that the heart of SHR shows an overactivity of the proximal steps of insulin signalling which cannot be further increased by the exposure to the hormone. This abnormality may account for the marked increase of basal cardiac glucose uptake and the loss of insulin-stimulated glucose uptake observed in SHR.

Vascular remodeling and ET-1 expression in rat strains with different responses to chronic hypoxia.

Chronic hypoxia leads to a greater degree of pulmonary hypertension in the Wistar-Kyoto (WKY) rat than in the Fischer 344 (F-344) rat. We questioned whether this difference is associated with baseline differences in pulmonary artery anatomy, a greater degree of hypoxia-induced pulmonary vascular remodeling in the WKY rat, and/or differences in expression of endothelin (ET)-1. Male F-344 and WKY rats were maintained in normoxia or normobaric hypoxia for 21 days. Morphometry revealed that baseline pulmonary artery anatomy was similar in the two strains. However, during chronic hypoxia, the WKY rats developed a greater degree of muscularization of small pulmonary arteries. Baseline plasma and lung immunoreactive ET-1 levels were similar in the WKY and F-344 rats and increased significantly during hypoxia in the WKY rats. Northern analysis demonstrated increased lung preproET-1 mRNA during hypoxia in both strains, with a greater increase in WKY rats. Immunostaining demonstrated increased ET-1 in bronchial epithelium and peripheral pulmonary arteries during hypoxia, although to a greater degree in the WKY rats. We conclude that the WKY strain demonstrates increased susceptibility to hypoxia-induced pulmonary vascular remodeling compared with the F-344 strain and that increased lung and circulating ET-1 levels during hypoxia may partly explain this difference.