Adult Spontaneously Hypertensive Research Articles

Early structural alterations of intrinsic cardiac ganglionated plexus in spontaneously hypertensive rats.

Persistent arterial hypertension leads to structural and functional remodeling of the heart resulting in myocardial ischemia, fibrosis, hypertrophy, and eventually heart failure. Previous studies have shown that individual neurons composing the intracardiac ganglia are hypertrophied in the failing human, dog, and rat hearts, indicating that this process involves changes in cardiac innervation. However, despite a wealth of data on changes in intrinsic cardiac ganglionated plexus (GP) in late-stage disease models, little is known about the effects of hypertension on cardiac innervation during the early onset of heart failure development. Thus, we examined the impact of early hypertension on the structural organization of the intrinsic cardiac ganglionated plexus in juvenile (8-9 weeks) and adult (12-18 weeks) spontaneously hypertensive (SH) and age-matched Wistar-Kyoto (WKY) rats. GP was studied using a combination of immunofluorescence confocal microscopy and transmission electron microscopy in whole-mount preparations and tissue sections. Here, we report intrinsic cardiac GP of SH rats to display multiple structural alterations: (i) a decrease in the intracardiac neuronal number, (ii) a marked reduction in axonal diameters and their proportion within intracardiac nerves, (iii) an increased density of myocardial nerve fibers, and (iv) neuropathic abnormalities in cardiac glial cells. These findings represent early neurological changes of the intrinsic ganglionated plexus of the heart introduced by early-onset arterial hypertension in young adult SH rats.

Systemic and local administration of vasopressin differently affect hemodynamic and respiratory parameters in normotensive and hypertensive rats

IntroductionUpregulation of vasopressinergic system and increased chemoreflex activity contribute to essential hypertension. Vasopressin (AVP) V1a receptors (V1aRs) were found in the brain stem structures involved in the control of breathing and in the carotid bodies (CBs). It has also been shown that in normotensive rats intravenous (i.v.) and local (intra‐carotid, i.a.) AVP administration results in different hemodynamic and respiratory response.PurposeWe aimed at finding out how systemic (i.v.) and local (i.a.) administration of AVP affects cardiorespiratory system via V1aRs in normo‐ and hypertensive rats and if V1aRs are expressed in CBs in spontaneously hypertensive (SHR) and normotensive Wistar‐Kyoto (WKY) rats.MethodsThe study was performed on urethane‐anesthetized adult male WKY (n=7) and SHR rats (n=7). Animals were implanted with vascular catheters into femoral vein (i.v. infusions), femoral artery (hemodynamic parameters) and external carotid artery (local infusions), as well as the tracheal tube (respiratory parameters) and subcutaneous ECG electrodes. After obtaining baseline parameters, the arterial chemoreflex was triggered with i.v. administration of potassium cyanide (KCN) (30 μg/100 μL). Bolus of AVP was given i.v. (10 ng/100 μL) and i.a. (5 ng/50 μL). After stabilization of hemodynamic and respiratory parameters, V1a receptor was blocked by administration of V1aR antagonist (d(CH2)51,Tyr(Me)2,Arg8)‐Vasopressin; 5 μg/100 μL) and AVP and KCN infusions were repeated. After measurements, carotid bodies (CBs) were collected and immunostained for V1aRs and visualized with confocal microscopy.ResultsResting mean arterial blood pressure (MABP), heart rate (HR) and minute ventilation (MV) were significantly higher in SHR rats than in WKY control. In both groups hemodynamic and respiratory response to pharmacological trigger of the reflex occurred, however increase in MABP and MV were significantly greater in SHR than in WKY rats. Intravenous AVP administration caused an increase in MABP, but ventilatory inhibition only in SHR rats. Intra‐arterial AVP infusion caused a modest increase in MABP in both groups, but inhibition of ventilation only in SHR rats. Blockade of V1aR abolished the effects of both systemic and local AVP administration. Furthermore, V1aR antagonist decreased the pressor component of the chemoreflex, however it did not influence ventilatory response. Immunostaining revealed V1aRs in CBs in both groups.ConclusionsOur findings show that enhanced cardiorespiratory responses to activation of arterial chemoreflex and augmented pressor and ventilatory effects of systemic and local administrations of AVP are present in hypertensive rats and depend on V1aRs. Presence of V1aRs in CBs suggests that AVP may control cardiorespiratory system via arterial chemoreceptors.

Evaluation of Heart Rate Fragmentation in Spontaneously Hypertensive Rats

Rapid heart rate (HR) variations at respiratory frequency range are well accepted as a marker of cardiac vagal modulation. Nevertheless, a new pattern of ultra-rapid HR variation has been recently studied and named as heart rate fragmentation (HRF). HRF is a type of sinoatrial instability characterized by the presence of numerous inflections points (from one bit to another) in RR interval time series. HRF has been shown to be increased in aging and coronary diseases and seems to be linked to the risk life-threatening cardiovascular events and death. This study aimed to evaluate the HRF in a rat model of spontaneous hypertension. Unanesthetized freely moving spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats at 2 distinct ages, 4 to 6 weeks (young) or 12 to 15 weeks (adult), had their electrocardiogram recorded for 40 minutes. Series of RR intervals were generated and transformed into a sequence of symbols “-1”, “0” or “1” when the difference between successive RR values (transitions) was positive, zero, or negative, respectively. Transitions between symbols “-1” and “1” were labeled as “hard” (H) inflection points while those between “-1” (or “1”) and “0” were labeled as “soft” (S) inflection points. Next, sequences of 4 consecutive symbols (words - W) were distributed according to the number and type of transition they enclose. The total percentage of inflection points (PIP), the percentage of words with zero (W0), one (W1), two (W2) or three (W3) inflection points, as well as percentage of words enclosing only hard (WH), soft (WS) or mixed (WM), i.e., containing both types of inflection points, were quantified. PIP and W3 were lower in the young and adult SHR when compared to the counterparts WKY. In contrast, young and adult SHR showed a higher percentage of W0, W1 and W2 compared to WKY.Regarding the type of transition, the percentage of WH was lower, while the WS was higher, in young and adult SHR when compared to WKY counterparts. The percentage of WM was higher only in young SHR. In conclusion, although evidences indicate that cardiovascular diseases lead to an increase in HRF, we have shown lower HRF in hypertensive rats, with or without the presence of the hypertensive phenotype. However, the mechanisms giving rise to HRF are still unknown. Future studies must be conducted to evaluate whether the HRF pattern observed in young and adult SHR is maintained in elderly animals and to elucidate the mechanisms behind HRF in SHR and normotensive rats.

Intravenous vasopressin leads to greater haemodynamic and respiratory responses in spontaneously hypertensive SHR rats than in normotensive controls

Introduction Increased activity of vasopressinergic system has been implicated in pathophysiology of essential hypertension. Intravenous or central administrations of vasopressin (AVP) were shown to affect not only hemodynamics, but also ventilatory function in rats. Receptors for AVP have been found in the brainstem structures involved in the control of breathing and in the carotid bodies. We hypothesized that given the involvement of AVP in essential hypertension and control of ventilation, AVP may differently affect hemodynamics and ventilation in spontaneously hypertensive (SHR) and in normotensive Wistar-Kyoto (WKY) rats. Purpose In the study we investigated the effects of intravenously administered AVP on hemodynamic and respiratory parameters under hypertensive and normotensive conditions. Methods The study was performed in urethane-anesthetizes adult male normotensive WKY (n=7) and hypertensive SHR rats (n=7). We implanted catheters into the femoral artery and femoral vein for recording mean arterial blood pressure (MABP) and for intravenous infusions, respectively. Additionally, we recorded minute ventilation (MV), respiratory rate (RR) and end-tidal CO2 (ET-CO2) via tracheal tube. We also placed subcutaneous ECG electrodes for heart rate (HR) monitoring. After obtaining baseline parameters, the arterial chemoreflex was triggered pharmacologically with intravenous (i.v.) administration of potassium cyanide (KCN) (30 microg/100 microL). After stabilization of hemodynamic and respiratory parameters, rats received i.v. administration of AVP (10ng/100μL) and recordings continued. Results SHR rats had significantly higher resting MABP, HR and MV than WKY controls. Both increases in MABP and MV and decrease in ET-CO2 were significantly greater in SHR than in WKY rats in response to pharmacologically triggered peripheral chemoreflex. One minute after administration of KCN, MV remained elevated above baseline and ET-CO2 was below baseline in SHR rats, whereas all respiratory parameters were normal in WKY rats. In SHR rats administration of AVP resulted in significantly greater increase in MABP than in WKY controls and was accompanied by reduction in MV and RR but no changes in HR. In WKY rats AVP resulted in smaller MABP increase accompanied by insignificant changes in respiratory parameters or HR. Conclusions Our findings confirm increased sensitivity of arterial chemoreflex in urethane-anesthetized SHR rats and suggest that AVP-dependent pressor and respiratory responses are enhanced in spontaneously hypertensive rats.

Haemodynamic effects of the flavonoid quercetin in rats revisited.

Background and PurposeThe flavonoid quercetin increased the in vitro potency of the α1‐antagonist tamsulosin to reduce phenylephrine‐dependent arterial contractions by 10‐fold. To examine if this supplement–drug interaction luxates hypotensive and orthostatic events in vivo, several set of studies were conducted in spontaneously hypertensive (SHR) and normotensive (Wistar Kyoto [WKY]) rats.Experimental ApproachFirst, in rats pretreated with quercetin or its vehicle, responses to phenylephrine and tamsulosin were examined. Second, tamsulosin‐induced changes in renal, mesenteric, hindquarter and carotid conductance were compared in quercetin‐ and vehicle‐treated rats instrumented with Doppler flow probes. Animals were also placed on a tilt table to record regional haemodynamic changes to orthostatic challenges. Third, adult SHR were instrumented with telemeters to measure 24‐hr patterns of BP. Recordings were made before and during a 5‐week oral treatment of quercetin. Finally, pre‐hypertensive SHR were treated with quercetin from 4 to 8 weeks of age and arterial pressure was measured at 8 and 12 weeks.Key ResultsPretreatment with quercetin did not influence the responses to phenylephrine and tamsulosin, in neither WKY nor SHR. While tamsulosin treatment and tilting lowered BP and increased conductance in all vascular beds, effect size was not influenced by pretreatment with quercetin. Prolonged treatment with quercetin, in either prehypertensive SHR or adult SHR with established hypertension did not lower BP.Conclusions and ImplicationsCumulatively, these data demonstrate that quercetin does not amplify haemodynamic effects of tamsulosin or tilting in vivo in rats and has no effect on BP development in SHR.

24-Hour Profile of Blood Pressure, Heart Rate, Excretion of Electrolytes, and Locomotor Activity in Wistar-Kyoto and SHR Rats Under Conditions of Free-Run Rhythm.

We presented the results of our study of chronostructure of BP, HR, electrolyte excretion, and locomotor activity under conditions of "free-run rhythm" (light deprivation). In adult male Wistar-Kyoto (normotensive) and SHR (spontaneously hypertensive) rats, BP, biopotentials of the heart (ECG), and locomotor activity were recorded over 24 h by telemetric monitoring and the rate of excretion of electrolytes (Na+, K+, Ca2+, and Mg2+) during the nighttime and daytime hours was measured. It was found that under free-run rhythm, 24-h profiles of BP, HR, excretory function of the kidneys, and locomotor activity underwent more considerable changes in normotensive Wistar-Kyoto rats in comparison with hypertensive SHR rats. However, hypertensive rats demonstrated pronounced changes in rhythmic characteristics of HR, which can restrict adaptation reserves of the cardiovascular system.

Differences in autonomic innervation to the vertebrobasilar arteries in spontaneously hypertensive and Wistar rats.

Essential hypertension is associated with hyperactivity of the sympathetic nervous system and hypoperfusion of the brainstem area controlling arterial pressure. Sympathetic and parasympathetic innervation of vertebrobasilar arteries may regulate blood perfusion to the brainstem. We examined the autonomic innervation of these arteries in pre-hypertensive (PHSH) and hypertensive spontaneously hypertensive (SH) rats relative to age-matched Wistar rats. Our main findings were: (1) an unexpected decrease in noradrenergic sympathetic innervation in PHSH and SH compared to Wistar rats despite elevated sympathetic drive in PHSH rats; (2) a dramatic deficit in cholinergic and peptidergic parasympathetic innervation in PHSH and SH compared to Wistar rats; and (3) denervation of sympathetic fibres did not alter vertebrobasilar artery morphology or arterial pressure. Our results support a compromised vasodilatory capacity in PHSH and SH rats compared to Wistar rats, which may explain their hypoperfused brainstem. Neurogenic hypertension may result from brainstem hypoperfusion. We previously found remodelling (decreased lumen, increased wall thickness) in vertebrobasilar arteries of juvenile, pre-hypertensive spontaneously hypertensive (PHSH) and adult spontaneously hypertensive (SH) rats compared to age-matched normotensive rats. We tested the hypothesis that there would be a greater density of sympathetic to parasympathetic innervation of vertebrobasilar arteries in SH versus Wistar rats irrespective of the stage of development and that sympathetic denervation (ablation of the superior cervical ganglia bilaterally) would reverse the remodelling and lower blood pressure. Contrary to our hypothesis, immunohistochemistry revealed a decrease in the innervation density of noradrenergic sympathetic fibres in adult SH rats (P<0.01) compared to Wistar rats. Unexpectedly, there was a 65% deficit in parasympathetic fibres, as assessed by both vesicular acetylcholine transporter (α-VAChT) and vasoactive intestinal peptide (α-VIP) immunofluorescence (P<0.002) in PHSH rats compared to age-matched Wistar rats. Although the neural activity of the internal cervical sympathetic branch, which innervates the vertebrobasilar arteries, was higher in PHSH relative to Wistar rats, its denervation had no effect on the vertebrobasilar artery morphology or persistent effect on arterial pressure in SH rats. Our neuroanatomic and functional data do not support a role for sympathetic nerves in remodelling of the vertebrobasilar artery wall in PHSH or SH rats. The remodelling of vertebrobasilar arteries and the elevated activity in the internal cervical sympathetic nerve coupled with their reduced parasympathetic innervation suggests a compromised vasodilatory capacity in PHSH and SH rats that could explain their brainstem hypoperfusion.

Respiratory modulated sympathetic activity: a putative mechanism for developing vascular resistance?

Sympathetic activity exhibits respiratory modulation that is amplified in hypertensive rats. Respiratory modulated sympathetic activity produces greater changes in vascular resistance than tonic stimulation of the same stimulus magnitude in normotensive but not hypertensive rats. Mathematical modelling demonstrates that respiratory modulated sympathetic activity may fail to produce greater vascular resistance changes in hypertensive rats because the system is saturated as a consequence of a dysfunctional noradrenaline reuptake mechanism. Respiratory modulated sympathetic activity is an efficient mechanism to raise vascular resistance promptly, corroborating its involvement in the ontogenesis of hypertension. Sympathetic nerve activity (SNA) exhibits respiratory modulation. This component of SNA is important - being recruited under cardiorespiratory reflex conditions and elevated in the spontaneously hypertensive (SH) rat - and yet the exact influence of this modulation on vascular tone is not understood, even in normotensive conditions. We constructed a mathematical model of the sympathetic innervation of an arteriole, and used it to test the hypothesis that respiratory modulation of SNA preferentially increases vasoconstriction compared to a frequency-matched tonic pattern. Simulations supported the hypothesis, where respiratory modulated increases in vasoconstriction were mediated by a noradrenergic mechanism. These predictions were tested in vivo in adult Wistar rats. Stimulation of the sympathetic chain (L3) with respiratory modulated bursting patterns, revealed that bursting increases vascular resistance (VR) more than tonic stimulation (57.8±3.3% vs. 44.8±4.2%; P<0.001; n=8). The onset of the VR response was also quicker for bursting stimulation (rise time constant=1.98±0.09s vs. 2.35±0.20s; P<0.01). In adult SH rats (n=8), the VR response to bursting (44.6±3.9%) was not different to tonic (37.4±3.5%; P=0.57). Using both mathematical modelling and in vivo techniques, we have shown that VR depends critically on respiratory modulation and revealed that this pattern dependency in Wistar rats is due to a noradrenergic mechanism. This respiratory component may therefore contribute to the ontogenesis of hypertension in the pre-hypertensive SH rat - raising VR and driving vascular remodelling. Why adult SH rats do not exhibit a pattern-dependent response is not known, but further modelling revealed that this may be due to dysfunctional noradrenaline reuptake.

Age‐dependent Changes of CO2 Chemoreflex and Blood Pressure (BP) in Juvenile and Adult Spontaneously Hypertensive Rats (SHRs)

Activation of central chemoreceptors by CO2 increases BP, sympathetic nerve activity (SNA), and breathing. Experiments using SHRs, a well‐established neurogenic hypertensive model, have shown that the high BP is associated with elevated SNA and peripheral chemoreflexes, and an impaired baroreflex. Earlier we showed that adult SHRs have enhanced ventilatory (VE) and BP responses to hypercapnia, and blocking both orexin receptors can normalize such enhanced responses and markedly lower BP. Here, using juvenile SHRs (P42‐60), we report that: 1) VE responses to normoxic‐hypercapnia and hyperoxic‐hypercapnia (179±25 &amp; 162±38 %increase respectively) are higher than that of age‐matched normal rats (118±22 &amp; 113±26 %increase, respectively), but lower than that of adult SHRs (226±39 % increase)(P&lt;0.05); 2) resting BP is higher than of age‐matched normal rats (130±12 &amp; 99±5mmHg respectively), but lower than that of adult SHRs (157±12mmHg)(P&lt;0.05). Summary, in SHRs 1) significant increases in both CO2 chemoreflex and BP are measureable in juveniles; 2) the enhanced CO2 chemoreflex persists while peripheral chemoreceptors were inhibited by hyperoxia indicate an important role for central chemoreflex in neurogenic hypertension. We suggest that the enhanced CO2 chemoreflex in early life may be causally linked to the development of neurogenic hypertension in SHRs, and modulation of the overactive CO2 chemoreflex could be beneficial in treating neurogenic hypertension. (HL 28066)

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.

Abstract 3584: Comparison of the severity of imatinib-induced cardiotoxicity in normotensive Sprague-Dawley (SD) and spontaneously hypertensive (SHR) rats

Abstract Imatinib (IMNB) is a promising type of chemotherapeutic agent that specifically targets tyrosine kinase pathway-dependent tumors. However, cardiotoxicity has been reported with clinical use of IMNB. The characteristics of IMNB-induced cardiac alterations are not completely defined. The present study sought to examine the influence of a concomitant disease such as hypertension on the cardiotoxic effects of IMNB. Groups of adult male SD or SHR were dosed with 50 (5/group) or 100 mg/kg (10/group) IMNB or water (10/group)(p.o.) daily for 14 days (dose of 50 mg/kg is approximately 2x recommended human dose of 600 mg/m2). Tissues and blood samples were collected 24 hours after the last dosing. The 100 mg/kg dose caused a slight reduction in the rate of body weight gain. Serum levels of glucose were decreased and alanine transaminase (ALT) were increased in both SD and SHR dosed with IMNB. Changes from control were most pronounced in SD given 100mg/kg IMNB (ALT=175% vs 118% and glucose=81% vs 91% compared to SHR). White blood cell counts were depressed in SHR but not in SD rats. Dose-dependent cardiac lesions were noted in the groups of SD and SHR given either dose of IMNB (blinded evaluation). Cardiac lesions were characterized by cytoplasmic vacuolization, myofibrillar loss, interstitial infiltration with chronic inflammatory cells and fibrosis (proliferation of myofibroblasts). Mean lesion scores (based on a scale of 0 to 3) were higher in SHR than in SD (100mg/kg-1.9 vs 1.25 and 50 mg/kg-1.5 vs 1.1, p&amp;lt;0.05)(Tukey-Kramer test). Increased serum levels of cardiac troponin I were detected in all IMNB-treated groups. The overall mean cTnI levels were higher in SHR (31.5, 41.3 and 53.9 pg/ml) compared to SD (6.8, 25 and 30 pg/ml) at the vehicle control, 50 and 100 mg/kg doses, respectively. These results indicate that hypertension as expressed in SHR appears to be a factor that can intensify the cardiotoxic effects of IMNB and that monitoring for cardiac troponin I may provide a sensitive means of detecting IMNB toxicity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3584.

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.

Alterations in heme oxygenase/carbon monoxide system in pulmonary arteries in hypertension.

Enhancement of the heme oxygenase/carbon monoxide (HO/CO) system has been shown to lower blood pressure (BP) in young (8 weeks), but not in adult (20 weeks) spontaneously hypertensive (SHR) rats. The reasons for this selective effect still remain puzzling. We investigated the effects of hemin on the HO/CO system of the pulmonary artery (PA) in SHR and Wistar-Kyoto (WKY) rats at different ages and evaluated the hemin-dependent changes in sGC and cGMP pathways. Hemin administration resulted in an evident reduction of BP (from 148.6 +/- 3.2 to 125.8 +/- 2.6 mmHg, P < 0.01) in young, but not in prehypertensive (4 weeks) or adult SHR or WKY rats at all ages. Coadministration of the HO inhibitor, chromium mesoporphyrin, with hemin, cancelled the BP-lowering effect of hemin. Remarkably, lower expression levels of HO-1, HO-2, and sGC paralleled with reduced HO activity and cGMP content were observed in PA from 8-week SHR rats, but not from adult SHR or WKY rats of all ages. Interestingly, hemin treatment restored these deficiencies, although the expression level of non-inducible HO-2 protein remained unchanged. We conclude that in young and prehypertensive SHR rats, an impaired HO/CO-sGC/cGMP system in the PA might be indicative of the pathogenesis and development of hypertension. In contrast, the HO/CO system in the PA of adult SHR rats was upregulated as a compensatory reaction to elevated BP and desensitization of the downstream targets of the sGC/cGMP pathway occurred.

NEPHRIN EXPRESSION IN THE POST-NATAL DEVELOPING KIDNEY IN NORMOTENSIVE AND HYPERTENSIVE RATS

Nephrin is a slit diaphragm protein and its expression in the developing kidney is largely unknown. In this study, we explored the expression of nephrin in the developmental kidney in spontaneously hypertensive (SHR) and in Wistar-Kyoto (WKY) rats at different time points, from day 5 after birth to adulthood. Real time RT-PCR, in situ hybridization and immunohistochemistry were used to assess and quantify gene and protein expression of nephrin in the kidney. SHR had hypertension at week 10 and albuminuria at week 20. Nephrin expression in both SHR and WKY increased from day 5 to adulthood. Furthermore, both gene and protein expression of nephrin were significantly lower in SHR after birth when compared to WKY at the same age. These findings suggest that both in normotensive and hypertensive rats, nephrin expression increased from birth to the adult age and that down-regulation of nephrin in SHR evident from the early developmental kidney to adulthood may contribute to the development of albuminuria in adult SHR.

Primary and adaptive changes of A-type K+ currents in sympathetic neurons from hypertensive rats.

The A-type K+ current (IA) of superior cervical ganglion neurons acutely isolated from spontaneously hypertensive (SHR) and age-matched Wistar-Kyoto (WKY) rats was compared under whole cell voltage clamp. Activation parameters were similar in each strain. Steady-state inactivation was shifted approximately -6 mV in SHR, where one-half inactivation occurred at -81 mV vs. -75 mV in WKY rats. The shift was not present in prehypertensive SHR but remained in adult enalapril-treated SHR and, therefore, may represent a primary alteration of IA properties. IA amplitudes evoked from physiological potentials were similar, despite inactivation of a greater fraction of the current in the SHR. Comparing maximal IA densities revealed that current density is elevated in the SHR, which compensates for the inactivation shift. Current density decreased with age in WKY neurons but did not significantly decline in SHR neurons unless hypertension was prevented with enalapril. Thus adult SHR neurons may retain a high IA density as an adaptive response to offset potential hyperexcitability resulting from the hyperpolarized IA inactivation.

Changes of plasma L-arginine levels in spontaneously hypertensive rats under induced hypotension.

Nicardipine, a dihydropyridine type calcium channel blocker, was infused at two flow-rates into spontaneously hypertensive (SH) and control normotensive Wistar-Kyoto (WKY) rats (young, 6-week-old and adult, 23-week-old, n = 5) under pentobarbital anesthesia, to cause hypotension. Mean arterial blood pressure and the concentrations of plasma amino acids and norepinephrine (NE) were measured before infusion and at each step of the infusion. The reduction in blood pressure caused by nicardipine induced a decrease in plasma L-arginine concentration in both young and adult SH rats, this effect being larger in adult rats. There was no significant change in plasma levels of L-arginine in age-matched WKY rats. The concentration of other amino acids did not change in both rat strains. On the contrary, there was an increase in plasma NE concentration in both SH and WKY rats after infusion with nicardipine. Plasma L-arginine concentration showed a good inverse correlation with the logarithm of plasma NE concentration in SH and WKY rats and the correlation was expressed as Y = -alpha log(X) + m (Y, plasma L-arginine concentration (nmol/mL); X, plasma NE concentration (pmol/mL); alpha, a slope; and m, an intercept). alpha, 43.0 and 4.35 for 23-week-old SH and WKY rats, respectively, and 17.0 and 4.0 for 6-week-old SH and WKY rats, respectively. The present data together with previous data suggest a direct noradrenergic stimulation of the synthesis of nitric oxide (NO) from L-arginine. The findings also indicate an impairment of the L-arginine metabolism or pools in SH rats compared with WKY rats. The deficiency of L-arginine increases with the age of SH rats and could be related to the development and maintenance of hypertension due to inefficient production of NO.

Regulation of norepinephrine transport system by angiotensin II in neuronal cultures of normotensive and spontaneously hypertensive rat brains.

Brain angiotensin II (Ang II) plays a key role in blood pressure control in part by interacting with catecholamines (CA) and by stimulation of sympathetic pathways. The significance of Ang-CA interaction is further heightened by the presence of a hyperactive brain Ang II system in spontaneously hypertensive (SH) rat, a genetic model for essential hypertension. Neuronal cells in primary culture from the hypothalamus-brainstem that mimic in vivo situations in so far as many cellular actions of Ang II are concerned, have been used in the present study to elucidate Ang II regulation of CA by determining its cellular action on the norepinephrine transporter (NET) system. Ang II causes both acute and chronic stimulation of [3H]-norepinephrine (NE) uptake in neuronal cultures of Wistar Kyoto (WKY) rat brain. Acute stimulation begins as early as 5 min, reaches maximal levels in about 30 min in the presence of 100 nM Ang II, and is blocked by losartan, a specific antagonist for AT1 receptor subtype. In addition, this acute stimulation appears to be a posttranscriptional event and does not involve protein kinase C (PKC) or NET gene transcription. Chronic stimulation of [3H]-NE uptake by Ang II persists throughout the duration of Ang II incubation (24 h), is dose dependent, and is also mediated by AT1 receptor subtype. However, chronic stimulation of [3H]-NE uptake involves PKC, cfos, and NET gene transcription. Ang II also stimulates [3H]-NE uptake in neuronal cultures of SH rat brain, both acutely and chronically, by mechanisms similar to those observed in neuronal cultures of WKY rat brain. The stimulation of NET by Ang II is 2-fold higher than that seen in WKY and is consistent with increased AT1 receptor gene transcription and increased functional AT1 receptors in SH rat brain neurons compared with WKY rat brain neurons. The Ang II stimulation of the NET system is also higher in adult SH compared with WKY rats in vivo. These observations show that 1) Ang II stimulates the NET system both acutely and chronically, the former involving activation of preexisting transporters and the latter involving NET gene transcription and translation; and 2) Ang II stimulation of the NET system is elevated in SH rat brain neurons.

Maternal influences on adult blood pressure of SHRS: A single pup cross-fostering study

To examine the effects of the preweanling maternal environment on the development of adult blood pressure, individual spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) normotensive pups were reciprocally cross-fostered between mothers of the same or opposite strain. With this design, each SHR and WKY foster mother reared 7 of her own pups and 1 SHR or WKY foster pup. All litters were weaned at 21 days of age and body weights were obtained. At 110 days of age, SHR and WKY males were weighed and surgically prepared with chronic tail artery catheters. One day later, basal measures of mean arterial pressure (MAP, mmHg) and heart rate (HR, beats per min) were obtained while animals were resting and undisturbed in their home cages. Our findings indicate that adult SHRs reared by WKY foster dams displayed significant reductions in MAP compared to SHRs that were reared by their natural mothers or by SHR foster mothers. In contrast, MAPs of WKYs did not differ across rearing conditions. Weanling body weights of cross-fostered SHRs were significantly greater than control-reared SHRs while weanling body weights of cross-fostered WKYs were significantly lower than control-reared WKYs. However, by 110 days of age, there were no treatment-related effects on body weights of males of either strain. These findings underscore the importance of genotype × maternal environment interactions during the preweanling period for the development of cardiovascular phenotype in SHRs.

Delivery of angiotensin II type 1 receptor antisense inhibits angiotensin action in neurons from hypertensive rat brain.

Increased brain angiotensin II (AII) type 1 receptor (AT1R) expression has been implicated in the hyperactive brain angiotensin system and the development and maintenance of hypertension in the genetically spontaneously hypertensive (SH) rat. Neuronal cells in primary culture from the cardioregulatory-relevant brain areas (hypothalamus/brainstem) mimic increased brain AT1R gene expression and AT1R function of the adult SH rat. They have been utilized in the present study to determine whether cellular actions of AII could be regulated by the transfer of AT1R antisense (AT1R-AS) with the use of a retroviral-mediated gene delivery system developed for the central nervous system cultures. AII stimulates norepinephrine (NE) uptake in neuronal cultures of both normotensive (Wistar Kyoto) and SH rat brains. This neuromodulatory action is mediated by the AT1R subtype, is significantly higher in SH neurons, and is associated with a parallel stimulation of mRNAs for c-fos and NE transporter. Infection of neuronal cultures with a retrovirus vector that contains AT1R-AS (LNSV-AT1R-AS) results in an inhibition of AT1R-mediated stimulation of both c-fos and NE transporter mRNA, as well as NE uptake in both strains of rats; however, the inhibition is more pronounced in SH neurons compared with Wistar Kyoto rat brain neurons. The higher sensitivity of the SH rat brain neurons is further supported by our observation that a certain dose of LNSV-AT1R-AS that fails to induce inhibition of cellular actions of AII in WKY neurons causes a significant inhibition of AII actions in SH neurons. These observations show that retrovirally mediated delivery of AT1R-AS could be used to selectively control the actions of AII in primary neuronal cultures from SH rat brain.

Glomerular Losartan (DuP 753)-Sensitive Angiotensin II Receptor Density Is Increased in Young Spontaneously Hypertensive Rats

There is increasing evidence that an activated intrarenal renin-angiotensin system (RAS) alters renal hemodynamics and fluid balance and that such events may lead to the development of hypertension. To examine the role of the glomerular RAS in the development of hypertension in the spontaneously hypertensive (SHR) rat, we studied angiotensin (ANG) II receptors in isolated glomeruli from young (4- to 5-wk-old) and adult (10- to 12-wk-old) SHR and from age-matched, normotensive Wistar-Kyoto (WKY) rats. Glomerular ANG II receptor density in young SHR is 3-fold higher than in age-matched WKY rats (2033 +/- 154 versus 742 +/- 151 receptors/microns2; p < 0.05) and 1.5-fold higher than in adult SHR and WKY rats (1128 +/- 85 and 1198 +/- 181 receptors/microns2, respectively; p < 0.05). Additional studies demonstrated that the differences in receptor density are not related to disparity in receptor occupancy and that they are also independent of systemic ANG levels. Suppression of RAS by ANG converting enzyme inhibitors resulted in a 3-fold increase in receptor density in young SHR rats and a 4.5-fold increase in young WKY rats; receptor density remained greater in young SHR rats (5915 +/- 318 versus 3358 +/- 234 receptors/microns2, p < 0.05). Furthermore, competitive binding experiments using the nonpeptide ANG II antagonists losartan (AT1) and PD 123319 (AT2) indicate that the greater ANG II receptor density in the young SHR rats represents an increase in the number of a single population of AT1 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)