Normotensive Rat Strains Research Articles

Modulation of Blood Pressure through Microbiome Exchange between Milan Normotensive and Hypertensive Rat Strains

Modulation of Blood Pressure through Microbiome Exchange between Milan Normotensive and Hypertensive Rat Strains

Real‐Time dynamics of renal autoregulatory responses to BP changes in conscious, normotensive and hypertensive rat strains

Renal autoregulatory (AR) mechanisms are believed to insulate RBF and GFR from the continuously fluctuating systemic pressures and protect the glomerular capillaries from barotrauma by preventing glomerular transmission of systemic hypertension. However, renal AR has usually only been assessed by the degree to which RBF is restored to baseline after step changes in BP are imposed, generally under anesthesia. AR indices (% changes in RBF / % changes in BP) are used to quantitate the magnitude of the AR compensation. However, such methods do not provide an assessment of the real time dynamics of AR responses to the spontaneously occurring BP fluctuations in real time. We have recently described novel analytic methods to characterize both the magnitude and the kinetics of such AR responses to BP fluctuations in conscious Sprague‐Dawley rats with intact (controls) and impaired AR (3/4 nephrectomy) and/or calcium channel blockade (JASN 31(2):324‐336, 2020). Essentially, AR indices were calculated for adjacent segments of varying lengths (0.5 – 20 sec) which exhibited a MAP difference of at least 5 mmHg. These studies indicated a much greater rapidity of the normal AR response than observed using standard methods under anesthesia with the bulk of AR compensation (>50%) occurring within 2.5 sec with complete compensation occurring more slowly by ~10 sec. This rapid initial and likely myogenic component of the response was noted to be significantly slower in states of impaired renal AR with <40% of AR compensation being achieved by 5 sec. To assess the generalizability of these pattern of AR responses and interpretations of rapid myogenic protection, similar AR analysis were performed on concurrent BP and RBF recordings of 1‐4 hr duration that had been obtained in conscious chronically instrumented hypertensive and normotensive rat strains in our laboratory for transfer function analysis in control SHR, SHRsp, Dahl S (DS) and R (DR) rats, and Sprague‐Dawley (SD) rats over the past 20 years (Fig. 1). The pattern of AR responses and compensation is remarkably similar in all rat strains except that the responses are even faster and stronger in hypertensive rats with ~80% compensation being achieved by 2.5 sec (Fig. 2). To further examine the impact of ambient BP on AR responses, AI were separately calculated when the ambient MAP was within 30 mmHg below (low BP) or above (high BP) the average MAP during the recordings for each strain. There was a clear trend for the AR responses to be stronger at higher ambient MAP, although statistical significance was not achieved in all strains because of the scatter in individual animal data (Fig. 3). These data suggest that in addition to genetic factors, ambient BP per se may modulate the dynamics of protective renal AR responses in conscious rats.

Fetal-adult cardiac transcriptome analysis in rats with contrasting left ventricular mass reveals new candidates for cardiac hypertrophy.

Reactivation of fetal gene expression patterns has been implicated in common cardiac diseases in adult life including left ventricular (LV) hypertrophy (LVH) in arterial hypertension. Thus, increased wall stress and neurohumoral activation are discussed to induce the return to expression of fetal genes after birth in LVH. We therefore aimed to identify novel potential candidates for LVH by analyzing fetal-adult cardiac gene expression in a genetic rat model of hypertension, i.e. the stroke-prone spontaneously hypertensive rat (SHRSP). To this end we performed genome-wide transcriptome analysis in SHRSP to identify differences in expression patterns between day 20 of fetal development (E20) and adult animals in week 14 in comparison to a normotensive rat strain with contrasting low LV mass, i.e. Fischer (F344). 15232 probes were detected as expressed in LV tissue obtained from rats at E20 and week 14 (p < 0.05) and subsequently screened for differential expression. We identified 24 genes with SHRSP specific up-regulation and 21 genes with down-regulation as compared to F344. Further bioinformatic analysis presented Efcab6 as a new candidate for LVH that showed only in the hypertensive SHRSP rat differential expression during development (logFC = 2.41, p < 0.001) and was significantly higher expressed in adult SHRSP rats compared with adult F344 (+ 76%) and adult normotensive Wistar-Kyoto rats (+ 82%). Thus, it represents an interesting new target for further functional analyses and the elucidation of mechanisms leading to LVH. Here we report a new approach to identify candidate genes for cardiac hypertrophy by combining the analysis of gene expression differences between strains with a contrasting cardiac phenotype with a comparison of fetal-adult cardiac expression patterns.

Hypertension and vulnerability to hemorrhagic shock in a rat model.

Trauma mortality may be increased in the presence of preexisting diseases such as chronic hypertension. We hypothesized that systemic and microvascular alterations accompanying chronic hypertension would increase the vulnerability to hemorrhage relative to normotensive controls in a rat model of hemorrhagic shock. We present a novel comparative hemorrhage model of shock vulnerability, quantified by "vulnerability curves" expressing physiological response to hemorrhage as a function of three matched shock metrics: cumulative blood volume, mean arterial pressure (MAP), and oxygen delivery (Do2). Responses were central hemodynamics and respiratory and muscle oxygenation obtained for one hypertensive (spontaneously hypertensive [SHR]) and two normotensive (Sprague-Dawley, Wistar-Kyoto) rat strains. Hemorrhagic shock was induced by incremental (0.5 mL) hemorrhage to cardiovascular collapse in anesthetized and mechanically ventilated animals. Shock vulnerability of SHR rats was primarily pressure-driven; in general, SHR exhibited the expected patterns of more rapid deterioration in MAP and Vo2 over smaller ranges of blood loss and Do2. Sternotomy-related depression of CO and thus Do2 in SHR meant that we could not test hypotheses related to the role of Do2 and contribution to perfusion differences between normotensive and hypertensive subjects. Insensitivity of lactate to strain effects suggests that lactate may be a reliable biomarker of shock status. Unexpected similarities between Wistar-Kyoto and SHR suggest strain-related effects other than those related to hypertension per se contribute to hemorrhage response; body size effects and genetic relationships could not be ruled out. Future studies should incorporate phylogenetically based methods to examine the role of hypertension and physiological response to hemorrhage across multiple strains.

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Objectives Research on the pathogenesis and treatment of preeclampsia is hindered by lack of animal models. Here, we tested the hypothesis that the Dahl Salt Sensitive (Dahl S) rat, a known model of hypertension and kidney disease, is also a spontaneous model of preeclampsia. Methods We compared pregnancy in the Dahl S to a normotensive control rat strain, Sprague Dawley (SD), and another model of genetic hypertension with normal cardiovascular adaptations to pregnancy, the Spontaneously Hypertensive Rat (SHR). Female rats were implanted with telemetry units (DSI) via the femoral artery, allowed to recover for 10 days, and then mated with males of their same strain. Uterine artery resistance index (UARI) was measured on gestational day (GD) 18 via Doppler ultrasound (Vevo770) in anesthetized animals (n = 5–12), and urine was collected via metabolic cage on GD19. Rats were euthanized on GD20, pups were measured, the number of fetal resorptions was noted, and placentas were harvested for further analysis. Results Mean arterial pressure (MAP), proteinuria, and UARI were significantly greater at late pregnancy in the Dahl S rat compared to SD and SHR (Table). In the control strains, MAP decreased during pregnancy as expected, but there was a rise in MAP in the Dahl S. Pup and litter sizes were significantly smaller in the Dahl S rat, with an increased number of fetal resorptions in the Dahl S rat, indicating intrauterine growth restriction is present in this strain (Table). Conclusions These data suggest that the Dahl S rat exhibits a superimposed preeclamptic phenotype during pregnancy that is distinctive from preexisting hypertension during pregnancy as seen in the SHR control. Strain MAP (mmHg) Δ MAP (mmHg) Proteinuria (g/day) UARI # of Pups per Litter Pup weight/maternal weight (g/kg) Percent fetal resorptions SD 94 ± 2.2 −10.9 ± 2.1 11.0 ± 5.9 0.50 ± 0.01 13.3 ± 1.9 10.9 ± 0.3 0 SHR 114 ± 10.7∗ −20.3 ± 10.5 4.2 ± 3.2 0.53 ± 0.04 11.2 ± 0.6 8.3 ± 0.3 0 Dahl S 166 ± 3.0∗# 8.6 ± 2.4∗# 253.7 ± 28.2∗# 0.71 ± 0.02∗# 6.5 ± 1.6∗ 6.7 ± 0.8∗ 17.1 ± 6.5∗# ∗p Disclosures E.E. Gillis: None. J.N. Mooney: None. M.R. Garrett: None. J.M. Sasser: None.

Variable reactive hyperemia in normotensive strains of rat.

Previous studies from our laboratory report variation in nitric oxide (NO)‐dependent arterial pressure within the same strain of normotensive Sprague–Dawley rat dependent upon the commercial vendor supplying the rats. Clinical assessment of endothelial NO activity and endothelial function in general has used postocclusion, flow‐mediated dilation (FMD). Therefore, this study was conducted to determine whether the reactive hyperemic response was different between two normotensive strains from two different suppliers, Sprague–Dawley (SD) and Wistar–Kyoto (WKY) rats from Charles River (CR) and Harlan Laboratories (H), respectively. Rats were anesthetized and the femoral artery was occluded for 5 min, with femoral blood flow measured continuously by use of an ultrasonic perivascular flow probe. The average area under the reactive hyperemic response curve (3‐min duration) was not different between SD rats from CR (80 ± 23 mL/min∙s; n = 6) and H (94 ± 16 mL/min∙s; n = 6). As previously reported, blood pressures were higher in the SD rats from H versus CR. WKY rats from both suppliers had significantly larger hyperemia; 371 ± 67 versus 281 ± 71 mL/min∙s (n = 5) for the CR and H WKY rats, respectively, but again, were not different between vendors. Blood pressures in WKY rats were similar between vendors. These results suggest that differences in NO bioactivity are not discernable with an adapted FMD protocol in the rat and that normotensive strains of rat can have large differences in reactive hyperemia despite having similar blood pressures.

Abuse and dependence liability analysis of methylphenidate in the spontaneously hypertensive rat model of attention-deficit/hyperactivity disorder (ADHD): what have we learned?

Methylphenidate is the most prescribed stimulant medication for attention-deficit/hyperactivity disorder (ADHD). Despite the well documented clinical benefits of the drug, several questions remain unanswered concerning the effects of extended methylphenidate use (e.g. can methylphenidate be abused by ADHD patients? does repeated methylphenidate treatment produce addiction?). Preclinical studies can help address the long-term safety of clinical treatments, moreover animal studies provide valuable information on the details of drug actions. The spontaneously hypertensive rat (SHR), bred from normotensive Wistar Kyoto rat strain, is considered as the best validated and the most widely used animal model of ADHD. We reviewed the findings of research reports that investigated the abuse and dependence liability of methylphenidate in SHR. In particular, we surveyed the studies which investigated the effects of methylphenidate pretreatment on subsequent methylphenidate-induced conditioned place preference or self-administration for they may give insights into the abuse or dependence liability of long-term methylphenidate treatment in ADHD.

Cardiorespiratory variability following repeat acute hypoxia in the conscious SHR versus two normotensive rat strains

A link between exaggerated chemoreceptor sensitivity and hypertension has been documented in the spontaneously hypertensive rat (SHR) but has also been questioned when comparisons with normotensive strains other than the Wistar Kyoto (WKY) rat are made. To further evaluate the link between hypertension and chemoreflex sensitivity, changes in cardiorespiratory variability in response to three successive bouts of 5 min of hypoxia (21%→10%) were evaluated in conscious male SHR, and WKY and Sprague Dawley (SD) rats (n=7-8/group). In response to the first bout of hypoxia, the change in respiratory frequency (RF) was greatest in the SHR, but the increase in mean arterial pressure (MAP) was similar in both SHRs and WKY rats and all strains demonstrated a similar rise in heart rate (HR). All strains showed some level of response accommodation during subsequent bouts of hypoxia. Spectral analysis of HR variability identified a significant difference in high frequency (HF) power between strains during hypoxia, including an increase in HF power in the WKY rats, a decrease in the SHRs and little overall change in the SD rats. Alternatively, all strains demonstrated a rise in systolic arterial pressure (SAP) variability in the low frequency (LF) range in response to hypoxia but the increase was greatest in the SHR. Since SAP LF power is linked to vasosympathetic tone, these results support the hypothesis that essential hypertension is linked to exaggerated sympathetic responses to chemoreceptor stimulation but confirm that estimation of augmented reflex function cannot be determined by quantifying simple changes in MAP or HR.

Distribution and localisation of Gα proteins in the rostral ventrolateral medulla of normotensive and hypertensive rats: Focus on catecholaminergic neurons

About 860 G-protein-coupled receptors (GPCRs) mediate their actions via heterotrimeric G-proteins. Their activation releases Gα from Gβλ subunits. The type of Gα subunit dictates the major signalling proteins involved: adenylyl cyclase, PLC and rhoGEF. The rostral ventrolateral medulla (RVLM), containing the rostral C1 (rC1) cell group, sets and maintains the tonic and reflex control of blood pressure and a plethora of inputs converge onto these neurons. We determined the relative abundance of 10 Gα subunit mRNAs, representing the four major families, within the RVLM, using quantitative RT-PCR. In situ hybridisation (ISH) combined with immunohistochemistry (IHC) was used to quantify and compare this expression in rC1 with that in the A1 and A5 cell groups. The relative abundance of Gα subunit mRNAs and a comparison of gene expression levels were quantitatively determined in normotensive and hypertensive rat strains. All 10 Gα mRNAs were detected in the RVLM of Sprague–Dawley (SD) rats with relative abundance such that Gαs>Gαi2>Gαo>Gαq>GαL>Gα11>Gαi3>Gαi1>Gα12>Gα13. The high abundance of Gα mRNAs signalling via adenylyl cyclase indicates the importance of associated GPCRs. Within the rC1 and A1 groups similar differential Gα mRNA expression profiles were seen with Gαs being found in all rC1 cells, Gα11 absent and Gαi3 rarely expressed. Thus functionally distinct subgroups exist within the rC1 and A1 cell groups as differing distributions of Gα subunits must reflect the array of GPCRs that influence their activity. In contrast, all A5 cells expressed all Gα mRNAs suggesting a functionally homogeneous group. When the 10 Gα mRNAs of the RVLM in spontaneously hypertensive rats (SHR) were compared quantitatively to Wistar-Kyoto (WKY), only Gαs and Gα12 were significantly elevated. However when the expression in normotensive SD and WKY was compared with SHR no significant differences were evident. These findings demonstrate a range of GPCR signalling capabilities in brainstem neurons important for homeostasis and suggest a prominent role for signalling via adenylyl cyclase.

Flow mediated dilation variation based on normotensive rat strain

Previous studies from this lab have suggested that nitric oxide (NO) plays a significant role in the maintenance of arterial pressure in the same strain of rats obtained from different animal vendors. Subsequently, we hypothesized that similar variations in NO and thus, endothelial function, could be found in different strains of rat. Flow mediated dilation (FMD) is traditionally a non‐invasive technique used clinically to assess endothelial function. The hyperemic response elicited using this in vivo technique is thought to be mediated by NO release from the endothelium. The goal of the present study was to determine whether the FMD hyperemic response was different between two normotensive strains from the same supplier, Sprague‐Dawley (SD) and Wistar‐Kyoto rats (WKY) from Charles River (CR). In anesthetized rats, the femoral artery was isolated and occluded for 5 minutes, with femoral blood flow measured continuously before, during and after occlusion by use of an ultrasonic perivascular flow probe. Arterial pressure was measured directly via a catheter inserted into the contralateral femoral artery. The clamp procedure was repeated four times in each rat and then averaged. The average area under the FMD response curve (3 minute duration) for the CR SD rats was 79.0 ± 22.9 mL/min·s (n=6) and 371.0 ± 67.4 mL/min·s (n=5) for the CR WKY rats. These results suggest differences in endothelial function in normotensive rats and could have broad implications for research involving these strains of rat.

Elevated vertebrobasilar artery resistance in neonatal spontaneously hypertensive rats

There is a strong correlation between increased vertebral artery resistance and arterial blood pressure in humans. The reasons for this increased resistance at high systemic pressure remain unknown, but may include raised sympathetic activity. With the recent finding that prehypertensive spontaneously hypertensive (PHSH) rats, which have raised sympathetic nerve activity, but a blood pressure comparable to normotensive rat strains, we hypothesized that its vertebrobasilar vascular resistance would already be raised and, as a consequence, would exhibit a more responsive Cushing response (e.g., brain ischemia evoked sympathoexcitation and a pressor response). We report that PHSH rats exhibited a remodeling of the basilar artery (i.e., increased wall thickness and lower lumen-to-wall thickness ratio) that occurred before the onset of hypertension. In a novel in vitro vascularly isolated, arterially perfused brain stem preparation of PHSH rats of 4-5 wk of age, brain stem vascular resistance was raised by ∼35% relative to age- and sex-matched normotensive rats (P < 0.05). In the in situ arterial perfused working heart-brain stem preparation, occlusion of both vertebral arteries in the PHSH rat resulted in a significantly greater increase in sympathetic activity (57 vs. 20%, PHSH vs. control; P < 0.01) that triggered a greater increase in arterial perfusion pressure (8 vs. 3 mmHg, PHSH vs. control; P < 0.01) compared with normotensive rats. These data indicate raised vertebrobasilar artery resistance before the onset of hypertension in the PHSH rat. With the raised responsiveness of the Cushing response in the PHSH rat, we discuss the possibility of brain stem perfusion as a central nervous system determinant of the set point of vasomotor sympathetic tone in the hypertensive condition.

Blood pressure increased dramatically in hypertensive rats after left hemisphere lesions with 6-hydroxydopamine

Plasma angiotensinase activity, nitric oxide and systolic blood pressure (SBP) were differently affected after unilateral intrastriatal injection of 6-hydroxydopamine (6-OHDA), depending on the brain hemisphere injured. Moreover, normotensive and hypertensive rats responded differently suggesting an asymmetry in the organization of the autonomic nervous system of the vessels. The aim of this study was to investigate the evolution of SBP and heart rate (HR) over time after nigrostriatal lesions in normotensive and hypertensive rat strains. Unilateral depletions of brain dopamine were performed by injecting 6-OHDA into the left or right striatum of normotensive and hypertensive rats. Vehicle without 6-OHDA was unilaterally injected in control (sham) groups. SBP and heart rate (HR) were measured in un-anesthetised animals 10 and 3 days before administration of 6-OHDA or vehicle and 3 and 25 days after treatment. In normotensive rats, at the end of study, SBP increased significantly from pre-lesioned values in left-lesioned animals but no differences were observed in right-lesioned or sham groups. Before sacrifice, there was a significant reduction from pre-lesion values in HR. In hypertensive animals, there was a highly significant increase of SBP in left-lesioned and sham left rats and a slight increase in right-lesioned but no differences were observed in sham right group. No differences in HR were observed throughout the study in the groups studied. The present results represent direct experimental evidence of an asymmetrical cardiovascular response to unilateral brain lesions, suggesting that left injury may have a worst prognosis.

Ascorbic Acid Levels and Neutrophil Superoxide Production in Blood of Pre-, Early and Late Hypertensive Stroke-Prone Spontaneously Hypertensive Rats

We compared ascorbic acid (AA) levels in the blood and TPA- and fMLP-stimulated superoxide (O2•−) production in neutrophils of pre-, early, and late hypertensive stroke-prone spontaneously hypertensive rats (SHRSP) with those of age-matched Wistar Kyoto rats (WKY), or two other normotensive strains of rats. Plasma and lymphocyte AA levels were about two-fold higher in SHRSP as early as 4 weeks old compared to WKY, and also higher than those of Wistar and Sprague-Dawley (SD) rats. Levels of AA were high in the liver and adrenal glands of SHRSP, indicating congenitally high AA levels. The production of O2•− in neutrophils was about two-fold higher in SHRSP than in WKY even at 4 weeks of age, and increased with age in both strains. Among SHRSP, AA levels in lymphocytes decreased at the late hypertensive stages with a decrease in hepatic l-gulono-γ-lactone oxidase (GLO) activities. These data suggest that bi-phasic AA levels in the blood of SHRSP comprise congenitally high levels and a decrease after persistent hypertension due to enhanced O2•− production and a decrease in de novo AA synthesis through GLO.

Effects on Atrial Fibrillation in Aged Hypertensive Rats by Ca 2+ -Activated K + Channel Inhibition

We have shown previously that inhibition of small conductance Ca(2+)-activated K(+) (SK) channels is antiarrhythmic in models of acutely induced atrial fibrillation (AF). These models, however, do not take into account that AF derives from a wide range of predisposing factors, the most prevalent being hypertension. In this study we assessed the effects of two different SK channel inhibitors, NS8593 and UCL1684, in aging, spontaneously hypertensive rats to examine their antiarrhythmic properties in a setting of hypertension-induced atrial remodeling. Male spontaneously hypertensive rats and the normotensive Wistar-Kyoto rat strain were divided in 2×3 groups of animals aged 3, 8, and 11 months, respectively. The animals were randomly assigned to treatment with NS8593, UCL1684, or vehicle, and open chest in vivo experiments including burst pacing-induced AF were performed. The aging spontaneously hypertensive rats were more vulnerable to AF induction both by S2 stimulation and burst pacing. Vehicle affected neither the atrial effective refractory period nor AF duration. SK channel inhibition with NS8593 and UCL1684 significantly increased the atrial effective refractory period and decreased AF duration in both the normotensive and hypertensive strains with no decline in efficacy as age increased. In conclusion, SK channel inhibition with NS8593 and UCL1684 possesses antiarrhythmic properties in a rat in vivo model of paroxysmal AF with hypertension-induced atrial remodeling. The present results support the notion that SK channels may offer a promising new therapeutic target in the treatment of AF.

Comparison of the Microvascular Network Resistance between Normotensive and Spontaneously Hypertensive Rats

Elevated blood pressure during hypertension has been associated with microvascular rarefaction defined by a loss of arterioles, capillaries and/or venules. Recent work in our laboratory suggests that rarefaction is more complex and is accompanied by network patterning alterations. However, the influences of these alterations on network resistance remain unclear. The object of this study was to compare microvascular network resistances across spontaneous hypertensive and normotensive rat strains over the time course of blood pressure elevation. Mesenteric tissues from age‐matched (4/7‐8/15‐16 weeks) male spontaneously hypertensive (SHR; n = 4/5/4 rats, 8/8/4 tissues), Wistar‐Kyoto (WKY; n = 4/2/4 rats, 8/8/4 tissues), and Wistar (n = 4/5/4 rats, 8/8/4 tissues) rats were harvested and immunolabeled with PECAM, an endothelial cell marker. Based on vessel lengths, diameters and an assumed pressure drop of 65 mmHg, resistances were calculated using a computational model. For the 7–8 week age group, WKY (34.9 ± 7.4 mmHg/mL) networks had significantly increased resistance compared to SHR (19.7 ± 5.3 mmHg/mL) and Wistar (15.7 ± 5.7 mmHg/mL) networks. No significant differences existed for the 4 and 15–16 week age groups. The results from this study suggest that in hypertension microvascular networks associated with rarefaction do not necessarily have elevated resistances.

Structural properties of lipid reconstructs and lipid composition of normotensive and hypertensive rat vascular smooth muscle cell membranes

Multiple cell membrane alterations have been reported to be the cause of various forms of hypertension. The present study focuses on the lipid portion of the membranes, characterizing the microviscosity of membranes reconstituted with lipids extracted from the aorta and mesenteric arteries of spontaneously hypertensive (SHR) and normotensive control rat strains (WKY and NWR). Membrane-incorporated phospholipid spin labels were used to monitor the bilayer structure at different depths. The packing of lipids extracted from both aorta and mesenteric arteries of normotensive and hypertensive rats was similar. Lipid extract analysis showed similar phospholipid composition for all membranes. However, cholesterol content was lower in SHR arteries than in normotensive animal arteries. These findings contrast with the fact that the SHR aorta is hyporeactive while the SHR mesenteric artery is hyperreactive to vasopressor agents when compared to the vessels of normotensive animal strains. Hence, factors other than microviscosity of bulk lipids contribute to the vascular smooth muscle reactivity and hypertension of SHR. The excess cholesterol in the arteries of normotensive animal strains apparently is not dissolved in bulk lipids and is not directly related to vascular reactivity since it is present in both the aorta and mesenteric arteries. The lower cholesterol concentrations in SHR arteries may in fact result from metabolic differences due to the hypertensive state or to genes that co-segregate with those that determine hypertension during the process of strain selection.

Arterial internal elastic lamina holes: relationship to function?

Internal elastic lamina (IEL) hole (fenestration) characteristics and myoendothelial gap junction (MEGJ) density were examined in selected resistance and conduit arteries of normal and diseased rat and mouse models, using conventional, ultrastructural and confocal microscopy methods. Selected vessels were those commonly used in functional studies: thoracic aorta, proximal and distal mesenteric, caudal, saphenous, middle-cerebral and caudal cerebellar artery. Rat and mouse strains and treatment groups examined were Dahl, Sprague Dawley, Wistar Kyoto, Wistar, spontaneously hypertensive (SHR), deoxycorticosterone (DOC) treated rat; and apolipoprotein E knockout, C57/BL6 and BALB/c mice. Vessel size (as IEL circumference), IEL hole and MEGJ density were quantified. In mesenteric arteries, the width of IEL holes and the percent of IEL occupied by holes were also determined. IEL hole density varied significantly within and between mesenteric artery beds, even among normotensive rat strains. Among the hypertensive rats (SHR and DOC), hole density in some vessels was higher in the normotensives than in the hypertensives within each strain, whereas in Dahl rats, hole density was similar between hypertensives and normotensives. Hole density was not correlated with the formation of intimal lesions in superior mesenteric artery. There was no positive general correlation between IEL hole and MEGJ density in resistance and conduit vessels. However, there was a positive correlation between the size of some resistance arteries and MEGJ density, although such a relationship did not hold for conduit vessels or during development, and there was no such relationship between vessel size and IEL hole density. Whilst IEL holes are obviously required for MEGJ communication, their presence is not an indication of contact-mediated communication, but rather may be related to the presence of sites for the low resistance passage of diffusion-mediated release of vasoactive endothelial and smooth muscle substances.

Reducing blood pressure in SHR with enalapril provokes redistribution of NHE3, NaPi2, and NCC and decreases NaPi2 and ACE abundance

To determine the effects of long-term angiotensin-converting enzyme inhibition (ACEI) and blood pressure (BP) lowering on renal sodium transporter abundance and distribution in spontaneously hypertensive rats (SHR), 9-wk SHR were treated with enalapril (30 mg.kg(-1).day(-1)) for 4 wk. BP decreased from 156 +/- 4 to 96 +/- 8 mmHg. Na(+)/H(+) exchanger isoform 3 (NHE3) and Na(+)-P(i) cotransporter type 2 (NaPi2) localized to the body of the microvilli (MV) in normotensive rat strains. In untreated SHR, NHE3 partially retracted from the body to base of the MV and NaPi2 retracted to subapical vesicles. After enalapril treatment of SHR, NHE3 fully retracted to the base of the MV and, by density gradient fractionation, NHE3, NaPi2, dipeptidyl peptidase IV, myosin VI, Na-Cl cotransporter, and cortical Na-K-Cl cotransporter redistributed from low-density (apical enriched) to high-density (endosome enriched) membranes. Enalapril decreased total abundance of myosin VI (to 0.51 +/- 0.18 of untreated), ACE (0.67 +/- 0.22), and cortical NaPi2 (0.83 +/- 0.10). Normalizing SHR BP with HRH (7.5 mg/day hydralazine, 0.15 mg/day reserpine, and 3 mg/day hydrochlorothiazide) did not change Na(+) transporter density distribution or abundance. We conclude that lowering BP to normal levels in SHR does not normalize Na(+) transporter distribution, rather, chronic ACEI treatment provokes retraction of Na(+) transporters and associated proteins from transport-relevant domains of apical membranes and/or reduces their abundance.

Strain Dependent differences in variance of heart rate and mean arterial pressure in normotensive rats

Variability of heart rate and of blood pressure (BP) are recognized risk factors for cardiovascular disease. BP is known to vary among inbred, normotensive rat strains, suggesting genetic control of cardiovascular variables. We assessed BP by telemetry 12–14 days after transmitter implantation in two normotensive strains and their offspring. Heart rate and mean BP were acquired every 2 minutes for 24 hrin 11 Brown Norway (BN) rats, 5 Wistar Kyoto (WK), 23 F1 offspring of BN × WK cross, and in 201 F2 (F1 × F1) rats. Average heart rate did not differ among the groups (WK–316±6, BN–319±4, F1–315±2, F2–318±1 (mean± SEM)) although heart rate variability, is expressed as standard deviation of the 24-hour record, was higher in WK rats (38.9±1.2) than in BN rats (30.0±1.0); both F1(36.7±1.0) and F2 (38.3±0.4) had heart rate standard deviations that were similar to the parental WK strain. In contrast, BP was lower in BN rats (88±1mmHg) than in F1 (90±1), F2 (93±1), or WK (100±3). Standard deviation of BP was higher in WK rats (9.3±0.5) than in BN (7.1±0.2) and in this case both F1 (7.0±0.2) and F2 (7.5±0.1) more closely resembled the parental BN strain. These results suggest WK-dominant inheritance of heart rate variance and BN-dominant inheritance of BP variance. The absence of a Mendelian assortment in F2 rats suggests contributions by more than one gene to variation of both heart rate variance and BP variance. Funded by NHLBI.

Carotid arteriotomy induces different temporal gene expression profiles in normotensive and hypertensive rat strains

Analysis of gene expression profiles in patients or in animal models affected by cardiovascular diseases may provide insight into therapeutic strategies. In this study, 3 rat strains, Wistar Kyoto (WKY), spontaneously hypertensive rats (SHR) and the Milan hypertensive rat strain (MHS), have been investigated to assess the influence of genetic background and/or of hypertension on gene expression in arteriotomy-injured carotid arteries (CAs). Expression profiles of genes, c-myc, AT1, AT2, ETA, ETB, Bcl-2, Bax and Bcl-X, were determined by reverse transcription-polymerase chain reaction (RT-PCR) in the acute phase, from 1 to 48 h, following CA arteriotomy. WKY, SHR and MHS show significant differences in gene expression profiles after CA arteriotomy. c-Myc mRNA is activated earlier and/or to a greater extent in hypertensive strains than in WKY (p<0.05). AT1 mRNA increases in WKY after injury, while it decreases in both SHR and MHS (p<0.05). AT2 shows the opposite behaviour, decreasing in WKY and increasing in hypertensive strains (p<0.05). ETA mRNA decreases in all strains although with different timing and levels, associated with a replacement by ETB mRNA (p<0.05). Bcl-2/Bax ratio gradually decreases in WKY, while it decreases only transiently in SHR and MHS 4 h after injury (p<0.05). Overall data indicate that therapeutic strategies for stenosis prevention should carefully consider the gene expression profile after injury, the genetic background, the kind of vascular trauma and the diseases affecting the animal model or the patient.