Biomedical subjects

S P Bishop

Publications and source records attributed to S P Bishop.

At least 19 recordsLinked to original sources

PubMed2001

Cyclosporine reduces left ventricular mass with chronic aortic banding in mice, which could be due to apoptosis and fibrosis.

A tacit assumption in studies of left ventricular (LV) hypertrophy is that left ventricular/body weight (LV/BW) reflects the extent of myocyte hypertrophy. The goal of the current investigation was to determine if there was another explanation for the reduced LV/BW observed after inhibiting calcineurin with cyclosporine during the development of pressure overload LV hypertrophy as compared with animals that did not receive cyclosporine. Accordingly, we examined the prevalence of fibrosis and apoptosis and measured cell size in the hearts from mice at 1 and 3 weeks after transverse aortic banding with and without chronic cyclosporine. Although LV/BW, compared to aortic banded vehicle treated mice, was reduced by 30% in aortic banded cyclosporine treated mice, myocyte cross sectional area was similar in both banded groups (346+/-9 microm2 v 336+/-13 microm2). The volume percent interstitial fibrosis was greater in aortic banded cyclosporine treated animals (1.4+/-0.2%) compared with aortic banded vehicle treated animals (0.9+/-0.2%, P<0.05) or in sham animals (0.6+/-0.1%). Surprisingly, lesions including myocytes containing iron were observed and were most prominent in aortic banded cyclosporine treated animals. Apoptosis, quantitated with TUNEL staining as percent of myocytes, was increased in aortic banded cyclosporine treated animals at 7 days (1.6+/-0.4%) compared with aortic banded vehicle treated animals (0.4+/-0.1%, P<0.01) and was still increased at 21 days. Immunoblotting demonstrated a decrease in the phosphorylation of Akt and Bad, and also Bcl-2 levels were reduced in aortic banded cyclosporine treated animals at 7 days compared with aortic banded vehicle treated animals. These proteins protect against apoptosis, and support the concept that cyclosporine inhibited the calcineurin pathway, resulting in enhanced apoptosis. Thus, the decrease in LV/BW in the aortic banded cyclosporine treated animals actually may be due, at least in part, to cell loss and death, as reflected by the enhanced fibrosis and apoptosis and the focal iron deposits in myocytes.

Animals↗

PubMed2000

Determinants of the cardiomyopathic phenotype in chimeric mice overexpressing cardiac Gsalpha.

Mice with overexpressed cardiac Gsalpha develop cardiomyopathy, characterized by myocyte hypertrophy and extensive myocardial fibrosis. The cardiomyopathy likely involves chronically enhanced beta-adrenergic signaling, because it can be blocked with long-term propranolol treatment. It remains unknown whether the genotype of the myocyte is solely responsible for the progressive pathological changes. A chimeric population in the heart should answer this question. Accordingly, we developed a chimeric animal, which combined cells from a transgenic overexpressed Gsalpha parent and a Rosa mouse containing the LacZ reporter gene, facilitating identification of the non-Gsalpha cells, which express a blue color with exposure to beta-galactosidase. We studied these animals at 14 to 17 months of age (when cardiomyopathy should have been present), with the proportion of Gsalpha cells in the myocardium ranging from 5% to 88%. beta-Galactosidase staining of the hearts demonstrated Gsalpha and Rosa cells, exhibiting a mosaic pattern. The fibrosis and hypertrophy, characteristic of the cardiomyopathy, were not distributed randomly. There was a direct correlation (r=0.85) between the extent of myocyte hypertrophy (determined by computer imaging) and the quantity of Gsalpha cells. The fibrosis, determined by picric acid Sirius red, was also more prominent in areas with the greatest Gsalpha cell density, with a correlation of r=0.88. Thus, the overexpressed Gsalpha can exert its action over the life of the animal, resulting in a local picture of cardiomyopathic damage in discrete regions of the heart, where clusters of the overexpressed Gsalpha cells reside, sparing the clusters of normal cells derived from the normal Rosa parent.

Animals↗

PubMed2000

Nitric oxide, an important regulator of perfusion-contraction matching in conscious pigs.

We examined whether nitric oxide (NO) inhibition during moderate reduction in coronary blood flow (CBF) would affect perfusion-contraction matching. Coronary stenosis (CS) was induced in conscious pigs, which resulted in a stable 39 +/- 1% reduction in CBF for 1.5 h. Ischemic zone wall thickening (IZWT) decreased by an average of 56 +/- 2% during CS from 2.7 +/- 0.2 mm. After reperfusion, myocardial stunning was observed, but this recovered without evidence of necrosis. After recovery and subsequent administration of systemic NO synthase inhibition (N(omega)-nitro-L-arginine, 25 mg. kg(-1). day(-1) x 3 days), CS for 1.5 h reduced CBF similarly but decreased IZWT significantly more, P < 0.05, by 89 +/- 5%. Myocardial stunning, i.e., the decrease in IZWT at 12 h post-CS, was more severe (-65 +/- 5% vs. -21 +/- 3%), P < 0.05. Furthermore, CS during NO synthase inhibition resulted in multifocal subendocardial areas of necrosis in the area at risk. These data suggest that in the intact, conscious pig, NO inhibition prevents perfusion-contraction matching, resulting in intensification of post-ischemic stunning and development of subendocardial necrosis.

Animals↗

PubMed2000

Peripheral vascular endothelial dysfunction and apoptosis in old monkeys.

To determine the effects of aging on vasoactivity in a primate model (Macaca fascicularis), 13 young male monkeys (aged 7.1+/-0.4 years) and 9 old male monkeys (aged 19.8+/-0.6 years) were chronically instrumented for measurement of left ventricular and aortic pressures and cardiac output. Total cholesterol, triglyceride, and fasting blood sugar levels were not different between the 2 groups. There were no significant differences in baseline mean aortic pressure and total peripheral resistance (TPR) in the young monkeys versus the old monkeys. TPR fell less (P<0.05) with acetylcholine (1 microg/kg) in old monkeys (-25+/-1%) than in young monkeys (-34+/-2%), whereas decreases in TPR with sodium nitroprusside were similar in old and young monkeys. There was no evidence of atherosclerosis, but apoptosis of endothelial cells was enhanced (P<0.05) in the aortas and femoral arteries, but not in the media, of the old monkeys. There was a relationship (r=0.62, P=0.013) between the incidence of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive endothelial cells and endothelial cell density in the femoral artery. The reduced endothelial cell density was also correlated (r=0.82, P<0.01) with depressed TPR responses to acetylcholine. Thus, vascular endothelial dysfunction was present in old monkeys without evidence of atherosclerosis, which may be due to endothelial apoptosis and reduced endothelial cell density.

Acetylcholine↗

PubMed1999

Differential expression of angiotensin-converting enzyme and chymase in dogs with chronic mitral regurgitation.

The current study tested the hypothesis that angiotensin-converting enzyme (ACE) and chymase expression are subject to different regulatory processes in the heart, as well as the lungs and kidneys and, as a result, have an important effect on the efficacy of ACE inhibitor treatment in modulating tissue angiotensin II (ANG II) levels in heart failure. A total of 18 dogs underwent the induction of mitral regurgitation and were followed for 5 months. Eleven dogs were untreated and seven received the ACE-inhibitor ramipril at a dose of 10 mg PO BID. Seventeen dogs underwent a sham-operation: six of these dogs were treated with ramipril for 3 months (10 mg PO BID) and 11 were untreated and followed for 3 months prior to sacrifice. In mitral regurgitation dogs, ANG II levels were increased >2-fold in left ventricle, lungs, and kidney, but were normalized with ACE inhibitor-treatment only in the left ventricle. In the left ventricle and lungs steady state ACE mRNA levels and ACE activities were increased 2-fold in treated and untreated mitral regurgitation dogs compared to shams (P<0.05, ANOVA). In contrast, chymase mRNA levels were decreased by >50% and chymase activity was increased in left ventricle (LV) of mitral regurgitation dogs (P<0.05). Neither chymase mRNA nor chymase activity could be detected in the kidney; however, kidney ACE mRNA and ACE activity were significantly upregulated in treated and untreated mitral regurgitation dogs (P<0. 05). These results suggest that ACE and chymase expression are regulated differentially in the dog in response to chronic mitral regurgitation and ACE inhibitor treatment. Further, these responses, as well as regulation of ANG II formation, are organ specific.

Animals↗

PubMed1999

Inducibility of sustained ventricular tachycardia in a closed-chest ovine model of myocardial infarction.

The two goals of this study were (1) to develop a closed-chest animal model of monomorphic ventricular tachycardia; and (2) to investigate the effect of dual site pacing on inducibility of ventricular tachycardia. In the first part of the study, 10 of 14 sheep underwent successful induction of myocardial infarction by temporary balloon occlusion of the left anterior descending coronary artery. After a follow-up period of 21-43 days, sustained monomorphic ventricular tachycardia could be induced during programmed electrical stimulation using a "clinical" stimulation protocol in 8 of the 10 sheep. The number of ventricular tachycardia episodes per animal varied between 5 and 70. Ventricular fibrillation was never induced during programmed electrical stimulation. Ventricular tachycardia episodes lasted from 30 seconds up to 15 minutes and were terminated by antitachycardia pacing or DC cardioversion. In the second part of the study, the effect of dual site stimulation on ventricular tachycardia inducibility was investigated. High current stimuli from an area within the infarcted zone were given with the S1 programmed stimulation protocol. This dual site stimulation showed no effect on ventricular tachycardia induction during programmed electrical stimulation. This animal model shows a high induction rate of sustained monomorphic ventricular tachycardia in the chronic phase of myocardial infarction. The high incidence of ventricular tachycardia inducibility provides a reliable tool to study new techniques for the prevention of ventricular tachyarrhythmias.

Animals↗

PubMed1999

An adenosine agonist and preconditioning shift the distribution of myocardial blood flow in conscious pigs.

The goal of this study was to determine whether the cardioprotective effects of an A1-receptor agonist and ischemic preconditioning (IPC) involve a shift in the pre-coronary artery occlusion (CAO) spatial distribution of myocardial blood flow, which might shed light on the mechanism of IPC and explain its heterogeneous effects. Accordingly, 60 min of CAO followed by 72 h of coronary artery reperfusion (CAR) was examined in three groups of conscious pigs 10-14 days after instrumentation with aortic and left atrial catheters and coronary artery occluders. Myocardial infarct size, expressed as a fraction of the area at risk (AAR), was reduced significantly (P < 0.05) by infusion of the A1 agonist (27.1 +/- 6.6%) and to a greater extent (P < 0.05) by IPC (11.6 +/- 5.1%) compared with infarct size in vehicle-treated animals (55.1 +/- 2.9%). Transmural myocardial blood flow (radioactive microspheres) in the AAR shifted toward lower levels after infusion of the A1 agonist (1.27 +/- 0.19 vs. 0.74 +/- 0.10 ml. min-1. g-1) or IPC (1.27 +/- 0.11 vs. 0.96 +/- 0.09 ml. min-1. g-1) but not after infusion of the vehicle (1.20 +/- 0.10 vs. 1.23 +/- 0.09 ml. min-1. g-1). This study demonstrated that both pretreatment with an adenosine A1 agonist and also IPC altered the spatial distribution of pre-CAO myocardial blood flow, which might reflect a downregulation of metabolic state and thus play a role in the cardioprotective effects of IPC.

Animals↗

PubMed1999

An alpha-cardiac myosin heavy chain gene mutation impairs contraction and relaxation function of cardiac myocytes.

Left Ventricular (LV) myocytes were isolated from 15-wk-old male mice bearing the Arg403 --> Gln alpha-cardiac myosin heavy chain missense mutation (alpha-MHC403/+), a model of familial hypertrophic cardiomyopathy. LV myocytes were classified morphologically: type I, rod shaped with parallel myofibrils; type II, irregularly shaped, shorter and wider than wild-type (WT) control cells, with parallel myofibrils; and type III, irregularly shaped with disoriented myofibrils. Compared with WT myocytes, alpha-MHC403/+ myocytes had fewer type I cells (WT = 74 +/- 3%, alpha-MHC403/+ = 41 +/- 4%, P < 0.01) and more type III cells (WT= 12 +/- 3%, alpha-MHC403/+ = 49 +/- 7%, P < 0.01). In situ histology also demonstrated marked myofibrillar disarray in the alpha-MHC403/+ hearts. With the use of video edge detection, myocytes were paced at 1 Hz (37 degrees C) to determine the effects of the mutation on myocyte function. End-diastolic length was reduced in mutant myocytes, but fractional shortening (% contraction) and sarcomere length were not. Velocity of contraction (-dL/dtmax) was depressed in mutant cells, but more in type II and III cells (-31%) than in type I cells (-18%). Velocity of relaxation (+dL/dt) was also depressed more in type II and III cells (-38%) than in type I cells (-16%). Using fura 2 dye with intracellular Ca2+ transients, we demonstrated that in alpha-MHC403/+ myocytes, the amplitude of the Ca2+ signal during contraction was unchanged but that the time required for decay of the signal to decrease 70% from its maximum was delayed significantly (WT = 159 +/- 8 ms; alpha-MHC403/+ = 217 +/- 14 ms, P < 0.01). Sarco(endo)plasmic reticulum Ca2+-ATPase mRNA levels in alpha-MHC403/+ and WT mice were similar. These data indicate that the altered cardiac dysfunction of alpha-MHC403/+ myocytes is directly due to defective myocyte function rather than to secondary changes in global cardiac function and/or loading conditions.

Action Potentials↗

PubMed1998

Ineffective perfusion-contraction matching in conscious, chronically instrumented pigs with an extended period of coronary stenosis.

Several models purported to represent hibernating myocardium involve a coronary stenosis (CS) to reduce blood flow (BF) and function without eliciting necrosis in anesthetized pigs. The goal of the present study was to determine whether sustained moderate reduction in coronary BF in conscious pigs induced hibernating myocardium, ie, perfusion-contraction matching with no necrosis. These experiments were conducted in conscious pigs chronically instrumented with a coronary artery BF probe and hydraulic occluder, left ventricular (LV) pressure gauge, and wall thickening (WT) crystals in the potentially ischemic and nonischemic zones. The hydraulic occluder was inflated to induce a stable 41+/-4% reduction in BF for 24 hours. Ischemic zone systolic WT fell initially with CS and then continued to decline during the period of CS even though blood flow did not change further, suggesting the induction of myocardial stunning. At 2 days after release of CS, WT was still depressed by 48+/-15%. Assessment of necrosis by histology or triphenyltetrazolium chloride showed 40+/-5% multifocal patchy necrosis interspersed with normal tissue involving the inner one third to one half of the ventricular wall. Regional myocardial BF (radioactive microsphere technique) was assessed by dividing the entire LV into an average of 488+/-59 pieces and examining the spatial distribution of BF within the area at risk (AAR). BF in the samples in the area of patchy necrosis was reduced (-66+/-4% from a baseline of 1.55+/-0.27 mL x min(-1) x g(-1)), whereas BF was maintained in samples in the AAR without necrosis (-2+/-7% from a baseline of 1.25+/-0.22 mL x min(-1) x g(-1)). These findings indicate that when hypoperfusion induced by CS in conscious pigs is sustained, the result is necrosis rather than hibernating myocardium. The remainder of the AAR, which lacked necrosis, might have been mistaken for hibernating myocardium had only histology been evaluated and BF not been measured and found to be at normal levels.

Animals↗

PubMed1998

Prevention of renovascular and cardiac pathophysiological changes in hypertension by angiotensin II type 1 receptor antisense gene therapy.

Hypertension produces pathophysiological changes that are often responsible for the mortality associated with the disease. However, it is unclear whether normalizing blood pressure (BP) with conventional therapy is effective in reversing the pathophysiological damage. The duration and initiation of treatment, site of administration, and agent used all appear to influence the reversal of the pathophysiological alterations associated with hypertension. We have previously established that retrovirally mediated delivery of angiotensin II type 1 receptor antisense (AT1R-AS) attenuates the development of high BP in the spontaneously hypertensive (SH) rat model of human essential hypertension. Our objective was to determine whether this attenuation of high BP is associated with prevention of other pathophysiological changes induced by the hypertensive state. Intracardiac delivery of AT1R-AS in neonates prevented the development of hypertension in SH rats for at least 120 days. Contractile experiments demonstrated an impaired endothelium-dependent vascular relaxation (acetylcholine) and an enhanced contractile response to vasoactive agents (phenylephrine and KCl) in the SH rat renal vasculature. In addition, the voltage-dependent K+ current density, which is believed to contribute to smooth muscle resting membrane potential and basal tone, was decreased in renal resistance artery cells of the SH rat. AT1R-AS treatment prevented each of these renal vascular alterations. Finally, AT1R-AS delivery prevented the pathological alterations observed in the SH rat myocardium, including left ventricular hypertrophy, multifocal fibrosis, and perivascular fibrosis. These observations demonstrate that viral-mediated delivery of AT1R-AS attenuates the development of hypertension on a long term basis, and this is associated with prevention of pathophysiological changes in SH rats.

Acetylcholine↗

PubMed1998

Hypertrophic remodeling: gender differences in the early response to left ventricular pressure overload.

OBJECTIVES: To identify gender differences in left ventricular remodeling, hypertrophy, and function in response to pressure overload due to ascending aortic banding in rats. BACKGROUND: Gender may influence the adaptation to pressure overload, as women with aortic stenosis have greater degrees of left ventricular hypertrophy and better left ventricular function than men. METHODS: Fifty-two weanling rats underwent ascending aortic banding (16 males, 18 females), or sham surgery (9 males, 9 females). At 6 and 20 weeks, rats underwent transthoracic echo Doppler studies, and closed-chest left ventricular pressures with direct left ventricular puncture. Perfusion-fixed tissues from eight rats were examined morphometrically for myocyte cross-sectional area and percent collagen volume. RESULTS: At 6 weeks after aortic banding, left ventricular remodeling, extent of hypertrophy, and function appeared similar in male and female rats. At 20 weeks, male but not female rats showed an early transition to heart failure, with onset of cavity dilatation (left ventricular diameter=155% vs. 121% of same-sex sham), loss of concentric remodeling (relative wall thickness=102% vs. 139% of sham), elevated wall stress (systolic stress=266% vs. 154% of sham), and diastolic dysfunction (deceleration of rapid filling=251% vs. 190% of sham). Left ventricular systolic pressures were higher in female compared with male rats (186+/-20 vs. 139+/-13 mm Hg), while diastolic pressures tended to be lower (14+/-4 vs. 17+/-4 mm Hg). CONCLUSIONS: Gender significantly influences the evolution of the early response to pressure overload, including the transition to heart failure in rats with aortic stenosis.

Adaptation, Physiological↗

PubMed1998

Retrograde coronary venous infusion of ethanol for ablation of canine ventricular myocardium.

INTRODUCTION: Permanent cure of reentrant ventricular tachycardia (VT) associated with coronary artery disease is difficult to achieve. Retrograde coronary venous infusion of ethanol for ablation of ventricular myocardium associated with reentrant tachyarrhythmias has several potential advantages, including use of physiologic mapping techniques and production of deeper, wider necrotic zones. METHODS AND RESULTS: Nine anesthetized dogs had baseline hemodynamic measurement, left ventriculography, coronary arteriography, occlusive coronary venography, and programmed electrical stimulation of the right ventricular apex and outflow tract. A balloon-tipped infusion catheter was advanced into a distal coronary venous branch, the balloon slowly inflated, and pure ethanol infused at volumes of 1.5, 3, or 5 cc. Hemodynamic measurements, angiography, ventriculography, and programmed electrical stimulation were repeated immediately and 1 week following ablation. Formalin-perfused hearts were serially sectioned and lesion volumes determined. Histologic examination of ablation beds then was performed. No significant difference was found in any hemodynamic measurement before or after ablation. Coronary arteriograms and left ventriculograms were unchanged after ablation. Nonsustained VT occurred in eight dogs during ethanol infusion; however, VT was not inducible in any dog before or after ablation. Infusion volumes of 3 cc or more were required to produce transmural lesions. CONCLUSION: Retrograde coronary venous infusions of ethanol using a balloon-tipped infusion catheter were effective in ablating ventricular myocardium. Retrograde chemical ablation did not itself result in inducible VT or adversely affect hemodynamic measurements or coronary arteries. Transmural myocardial necrosis, necessary in the ablation of VT associated with coronary artery disease, can be produced by higher infusion volumes.

Animals↗

PubMed1998

Selective large coronary endothelial dysfunction in conscious dogs with chronic coronary pressure overload.

Coronary vascular responses to acetylcholine (ACh, 3 micrograms/kg i.v.), nitroglycerin (NTG, 25 micrograms/kg i.v.), and a 20-s coronary artery occlusion (reactive hyperemia, RH) were investigated in seven conscious dogs with severe left ventricular (LV) hypertrophy and chronic coronary pressure overload (CCPO) due to supravalvular aortic banding and in seven control dogs. All dogs were instrumented for measurement of ultrasonic coronary diameter (CD) and Doppler coronary blood flow (CBF). LV-to-body weight ratio was increased by 82% in CCPO dogs. In control dogs, ACh increased CD (+ 5.9 +/- 1.7%). This response was reduced (P < 0.05) in CCPO dogs (+ 1.9 +/- 0.9%). Similarly, flow-mediated increases in CD after RH were blunted (P < 0.01) in CCPO (+ 2.1 +/- 0.8) vs. control dogs (+ 6.8 +/- 1.8%). In contrast, ACh and RH increased CBF similarly in both groups. Increases in both CD and CBF to NTG were not different between control dogs and CCPO. Peak systolic CBF velocity was greater, P < 0.01, in CCPO (94 +/- 17 cm/s) compared with control (35 +/- 7 cm/s) dogs, most likely secondary to the increased systolic coronary perfusion pressure (215 vs. 130 mmHg). Histological analyses of large coronary arteries in CCPO revealed medial thickening, intimal thickening, and disruption of the internal elastic lamina and endothelium. In contrast, small intramyocardial arterioles failed to show the intimal and endothelial lesions. Thus, in CCPO selective to the coronary arteries, i.e., a model independent from systemic hypertension and enhanced levels of plasma renin activity, endothelial control was impaired for both flow-mediated and receptor-mediated large coronary artery function, which could be accounted for by the major morphological changes in the large coronary arteries sparing the resistance vessels. The mechanism may involve chronically elevated systolic coronary perfusion pressure, CBF velocity, and potential disruption of laminar flow patterns.

Acetylcholine↗

PubMed1997

Angiotensin AT1 receptor inhibition. Effects on hypertrophic remodeling and ACE expression in rats with pressure-overload hypertrophy due to ascending aortic stenosis.

BACKGROUND: We tested the hypothesis that long-term administration of the specific angiotensin II subtype 1 (AT1)-receptor blocker BMS-186295 will regress hypertrophy and modify left ventricular angiotensin converting enzyme (ACE) expression in rats with ascending aortic stenosis. METHODS AND RESULTS: Six weeks after surgery, rats with ascending aortic stenosis were randomized to receive either the AT1-receptor blocker BMS-186295 50 mg.kg-1.d-1 (n = 49), amlodipine 2.5 mg.kg-1.d-1 (n = 48) as a positive control for systemic vasodilation, or no drug (n = 48) and compared with sham-operated rats (n = 39). Drug treatment was continued for 15 weeks. Left ventricular ACE mRNA levels were measured by ribonuclease protection assay. The left ventricular/body weight ratio was increased 43% in hearts from rats with untreated left ventricular hypertrophy (LVH) versus control hearts (P < .05). However, there was no difference in either the left ventricular/body weight ratio (2.78 +/- 0.08 versus 2.81 +/- 0.20 mg/g; P = NS) or myocyte cross-sectional area in the AT1-blocker-treated versus untreated LVH hearts. Amlodipine also showed no effect on regression of hypertrophy. In vivo left ventricular systolic pressure was significantly higher in untreated LVH versus sham-operated rats (193 +/- 8 versus 118 +/- 4 mm Hg; P < .05), and there was a similar severe elevation of left ventricular systolic pressure in the AT1-blocker- and amlodipine-treated LVH groups (189 +/- 9 and 188 +/- 16 mm Hg; P = NS versus untreated LVH). In vivo left ventricular end-diastolic pressure was higher in the untreated LVH than in the sham-operated rats (14.8 +/- 2.3 versus 7.0 +/- 0.5 mm Hg; P < .05). Left ventricular end-diastolic pressure was lower in the AT1-blocker-treated (11.0 +/- 1.7 mm Hg) and amlodipine-treated rats (11.5 +/- 1.8 mm Hg) and was similar to left ventricular end-diastolic pressure in the sham-operated rats (P = NS). Left ventricular ACE mRNA levels were elevated in untreated LVH rats but were normalized in both the AT1-blocker-treated rats and amlodipine-treated rats. CONCLUSIONS: Long-term AT1-receptor blockade did not regress LVH in rats with persistent systolic pressure overload due to ascending aortic stenosis. However, both AT1-receptor blockade and amlodipine improved in vivo left ventricular end-diastolic pressure in association with the normalization of left ventricular ACE mRNA levels.

Angiotensin Receptor Antagonists↗

PubMed1997

Inhibition of cardiac myocyte division in c-myc transgenic mice.

Overexpression of the c-myc protooncogene in the heart of transgenic mice has been demonstrated to result in cardiac enlargement due to increased myocyte hyperplasia during the fetal period. To determine the age of completion of the proliferative phase of myocyte growth in neonatal mice with c-myc overexpression, we used a transgenic (TG) mouse model in which c-myc overexpression is limited to the heart. Bromodeoxyuridine (BrdU) was given to TG and wild type (WT) mice (n=3/group) at 1, 2, 3, 5, 7, 10, 14, 16, 18 and 20 days of age to identify cells in S-phase of the cell cycle. Increased cardiac mass was present in TG compared to WT mice at all time periods (P<0. 05). Using computer assisted image analysis, myocardial total nuclear density (NT) in TG mice was 7-31% greater in both the left ventricle (LV) and the interventricular septum (IVS) than in WT at all ages (P<0.05), indicative of a smaller myocyte size. In WT mice, the labeling index (LI) remained almost constant at approximately 11-12% until 7 days of age, and then rapidly dropped to approximately 2% by 14 days and to less than 1% by 20 days. In contrast, LI in TG dropped continuously from birth to approximately 4% at 7 days and approximately 2% at 10 days of age (P<0.001). Thus, overexpression of the c-myc protooncogene is associated with enhanced hyperplastic growth of the heart during fetal development, and accelerated neonatal conversion to hypertrophic myocyte growth.

Animals↗

PubMed1997

Selective induction of the creatine kinase-B gene in chronic volume overload hypertrophy is not affected by ACE-inhibitor therapy.

Hypertrophied and failing myocardium has been shown to undergo creatine kinase (CK) isoform switching, resulting in increased MB and BB components. We tested the hypothesis that chronic volume overload hypertrophy due to mitral regurgitation in the dog causes CK isoenzyme switching and that this could be reversed by angiotensin converting enzyme inhibitor therapy. Thirteen adult mongrel dogs had mitral regurgitation induced by mitral valvular chordal rupture: six were treated with ramipril for 4 months and seven were untreated for 4 months. Twelve dogs were sham-operated: six received ramipril for 3 months and six were untreated. Left ventricular end-diastolic volume increased from 58+/-4 to 104+/-10 ml in untreated (P<0.001) and from 55+/-3 to 91+/-6 ml in treated dogs (P<0.01) as LV mass/volume ratio decreased in both untreated (1. 60+/-0.07 to 1.13+/-0.08 g/ml, P<0.001) and treated dogs (1.44+/-0.06 to 1.20+/-0.08 g/ml, P<0.01). CK-MB isoform was 7.4+/-1.1% in normal shams and increased to 13.5+/-1.9% and 18.1+/-3.0% in both treated and untreated mitral regurgitation dogs; respectively (P<0. 05). Steady state CK-B mRNA increased three-fold in treated and untreated dogs with mitral regurgitation (P<0.003) compared to normals, while CK-M mRNA expression did not differ in all groups. Thus, chronic volume overload hypertrophy of mitral regurgitation induces CK isoform switching by selective induction of the CK-B gene, and ramipril therapy does not affect this isoform switch. This may reflect a response to increased diastolic stress and more efficient energy utilization in the volume overloaded myocardium.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1997

Effects of chronic beta-adrenergic receptor stimulation in mice.

The goal of the present study was to determine the effects of chronic beta-adrenergic receptor stimulation with isoproterenol (ISO) on cardiac tissue, systemic trophic changes and on beta-adrenergic receptor desensitization in mice. Mice (n=36) received continuous ISO (30 microg/g/day) via osmotic minipump for 13 days. Left ventricle (LV)/body weight (BW) ratio was increased by 27% in ISO v control (CON) mice. The extent of cardiac hypertrophy induced by chronic ISO was offset in part by concomitant increases in body weight, which were greater in ISO than CON mice (22 v 8%), and occurred with increases in both muscle mass and brown fat to BW ratios. Histological analysis of mice revealed a three-fold increase in subendocardial interstitial connective tissue with no evidence of acute cellular necrosis or chronic inflammation. Acute i.v. ISO challenges induced dose-dependent increases in LV fractional shortening (FS) and ejection fraction (EF) using echocardiography (9 MHz), which were attenuated after chronic ISO, i.e. physiological desensitization was observed. Cellular mechanisms of beta-adrenergic receptor desensitization included decreases in beta-adrenergic receptor density (-49%) and decreased basal (-45%) and ISO-stimulated (-61%) adenylyl cyclase activities. Lesser decreases in forskolin-stimulated adenylyl cyclase activity (-16%) and adenylyl cyclase mRNA levels for both type V (-17%) and type VI (-23%) isoforms were observed following chronic ISO. Thus, chronic ISO (30 microg/g/day) induced cardiac hypertrophy without cellular necrosis, increased weight gain and clear physiological desensitization in mice, with more extensive biochemical mechanisms than expected from simple catecholamine-specific (homologous) desensitization.

Adenylyl Cyclases↗

PubMed1997

Pressure-independent effects of AT1-receptor antagonism on cardiovascular remodeling in aortic-banded rats.

To determine the role of angiotensin II-receptor blockade on cardiovascular remodeling in a pressure-overload model of cardiac hypertrophy, a subdiaphragmatic aortic band was placed in adult male Sprague-Dawley rats. Aortic-banded (AB) rats were left untreated or were losartan (Los; 250 mg/l) treated (AB-Los). Sham-operated (S) controls were either left untreated or treated with Los (S-Los). After 4 wk, rats were catheterized for measurement of mean arterial pressures [carotid (CMAP) and femoral (FMAP), in mmHg]. Hearts were perfused on a modified Langendorff system, and minimal coronary resistance (MCR) was determined. Hearts were then perfusion fixed, total and regional heart weights were recorded, and sections were processed for morphology. Changes in coronary artery medial thickness and perivascular fibrosis were assessed by quantitative image analysis. CMAP was significantly higher in AB and AB-Los than in S or S-Los (P < 0.05). There was no difference in FMAP in AB vs. S, but AB-Los and S-Los had lower FMAPs than S. Total heart weight and left ventricular weight-to-body weight ratios were increased in AB and AB-Los compared with S and S-Los (P < 0.05). MCR of AB was greater than S and S-Los. MCR of AB-Los was significantly lower than AB and was not significantly different from S and S-Los. In coronary vessels, medial thickness was greatest in AB, whereas there was no difference among AB-Los, S, and S-Los. Similarly, the increase in perivascular fibrosis was greatest in AB, and there was no difference among AB-Los, S, and S-Los. These data suggest that angiotensin II, independent of increased arterial pressure, is critical for the development of the vascular and fibrotic changes that occur in this model of pressure-overload hypertrophy.

Angiotensin II↗