Phosphorylase b kinase and phosphorylase a phosphatase activities in contracting vascular smooth muscle: stimulation by fatty acid.

The activities of phosphorylase b kinase and phosphorylase a phosphatase were determined during the phases of KCl-induced contraction in porcine carotid artery. Phosphorylase b kinase exhibited a biphasic pattern with activity increasing 70% above basal levels during the early phase of active force generation (45 s into contraction) followed by a decline in activity during the phase of steady-state tension maintenance. Phosphorylase a phosphatase was stimulated simultaneously with phosphorylase b kinase, with activity increasing 100% over basal levels at 45 s into contraction, but remaining elevated at 30 min. Incubation of arteries in 0.5 mM palmitate resulted in a 30% increase in basal activity of phosphorylase b kinase and 117% augmentation of basal phosphatase activity, with no further increase in activity of either enzyme with contraction. The results indicate that both the kinase and phosphatase are subject to regulation during contractile activation of the muscle, possibly by similar but not identical mechanisms.

Fatty acid alters glycogen metabolism in contracting vascular smooth muscle.

The purpose of this investigation was to study the effect of fatty acid on carbohydrate metabolism in contracting vascular smooth muscle. The glycogen content of porcine carotid artery incubated in media containing only glucose decreased markedly upon contraction with 80 mM KCl. In contrast, when 0.5 mM palmitate was included there was no decrease in glycogen. Furthermore, the maximal isometric force generated was 22% greater than in the absence of palmitate (P less than 0.001). Stimulation of glycogen phosphorylase a activity with contraction was also enhanced with palmitate. Palmitate had no effect on the levels of the high energy phosphates under any substrate condition. Thus, fatty acid profoundly affects glycogen metabolism and contractility in vascular smooth muscle.

Endothelial- and nitric oxide-dependent effects on oxidative metabolism of intact artery.

Oxidative metabolism and its possible modulation by nitric oxide (NO) was examined in endothelial-intact and endothelial-denuded segments of porcine carotid arteries. Endothelial-intact arteries displayed appropriate NO-mediated vasorelaxation to acetylcholine (ACh). Endothelial-denuded arteries demonstrated absent vasorelaxation to ACh stimulation and depressed contractile responsiveness to K(+) depolarization, which was normalized by inhibition of NO synthesis by N(omega)-nitro-L-arginine methylester (L-NAME). Confirmation that carotid arteries continued to produce NO despite removal of the endothelium was indicated by detection of NO metabolites in the incubation medium bathing the arteries. O(2) consumption and the oxidation of glucose and fatty acid were depressed in endothelial-denuded arteries. Depression of O(2) consumption and glucose oxidation was completely reversed by treatment with L-NAME. We conclude that endogenous NO produced by non-endothelial vascular cells depresses contractility, O(2) consumption, and oxidation of energy substrates in vascular smooth muscle. The endothelium may play a role in oxidative metabolism of vascular smooth muscle possibly by modulating the effects of NO produced by other cells of the vessel wall, or by other factors.

Effect of serum albumin on vascular smooth muscle metabolism.

In studies on metabolism of vascular smooth muscle, it was observed that incubation of intact porcine carotid artery strips with 3% bovine or porcine serum albumin had profound effects on the oxidation of substrates and O2 consumption. Arteries incubated over 180 min with charcoal-treated and dialyzed albumin demonstrated time-dependent stimulation of glucose oxidation (145%; P < 0.0001, n=6) and O2 consumption (116%; P< 0.001, n=6). These results were not mimicked by incubation with 3% solutions of ovalbumin or porcine skin gelatin. However, the oxidation of the medium chain fatty acid octanoate was inhibited in the presence of albumin over a broad range of octanoate concentrations (0.5-5.0 mM). Short chain fatty acid oxidation (acetate, 5 mM), in contrast, was not inhibited by albumin. Wash-out of albumin only partially reversed the stimulation of O2 consumption and incubation of arteries with a polyanionic compound, polyethylene sulfonate (5 mg/ml), blunted the stimulatory effect of albumin on O2 consumption. Albumin also produced anaplerosis of the Krebs cycle, and an increase in the content of glutamate and alanine (P < 0.005, n=8). The metabolic effects of albumin were associated with time-dependent uptake of albumin (30.9 +/- 1.5 nmol/g per 210 min; P<0.01, n=15). ATP-dependent proteolysis of the albumin taken up was also observed. These results demonstrate novel and important intracellular effects of serum albumin on energy metabolism of vascular smooth muscle.

Differential effects of fatty acids on glycolysis and glycogen metabolism in vascular smooth muscle.

The effects of fatty acids of different chain lengths on aerobic glycolysis, lactic acid production, glycogen metabolism and contractile function of vascular smooth muscle were investigated. Porcine carotid artery segments were treated with 50 microM iodoacetate and perchloric acid tissue extracts were then analyzed by 31P-NMR spectroscopy to observe the accumulation of phosphorylated glycolytic intermediates so that the activity of the Embden-Myerhof pathway could be tracked under various experimental paradigms. Aerobic glycolysis and lactate production in resting arteries were almost completely inhibited with 0.5 mM octanoate, partially inhibited with 0.5 mM acetate and unaffected by 0.5 mM palmitate. Inhibition of glycolysis by octanoate was not attributable to inhibition of glucose uptake or glucose phosphorylation. Basal glycogen synthesis was unchanged with palmitate and acetate, but was inhibited by 52% with octanoate incubation. The characteristic glycogenolysis which occurs upon isometric contraction with 80 mM KCl in the absence of fatty acid in the medium was not demonstrable in the presence of any of the fatty acids tested. Glycogen sparing was also demonstrable in norepinephrine contractions with octanoate and acetate, but not with palmitate. Additionally, norepinephrine-stimulated isometric contraction was associated with enhanced synthesis of glycogen amounting to 6-times the basal rate in medium containing octanoate. Contractile responses to norepinephrine were attenuated by 20% in media containing fatty acids. Thus, fatty acids significantly alter metabolism and contractility of vascular smooth muscle. Fatty acids of different chain lengths affect smooth muscle differentially; the pattern of substrate utilization during contraction depends on the contractile agonist and the fatty acid present in the medium.

Oxidation of acetate and octanoate and its relation to glucose metabolism in contracting porcine carotid artery.

The oxidation of octanoate and acetate was measured in segments of porcine carotid arteries to ascertain whether the oxidation of exogenous fatty acid substrates (acetate and octanoate) is augmented during contraction induced by K(+)-depolarization. The oxidation of acetate increased from 7 +/- 1 to 14 +/- 2 nmol/min/g (P < 0.01) during sustained isometric contraction. Octanoate oxidation increased from 11 +/- 1 to 14 +/- 1 nmol/min/g (P < 0.05). The rate of oxidation of neither acetate nor octanoate was affected by the presence or absence of glucose either in resting or contracting arteries Acetate or octanoate oxidation could account for the majority of O2 consumption during contraction. Octanoate but not acetate inhibited glucose uptake and glycolysis in resting muscles. In contrast to augmented acetate and octanoate metabolism during contraction, there was a "down-regulation" of glucose metabolism in contracting muscles as evidenced by a decrease in the rate of glucose uptake, glycolysis and lactic acid production during sustained isometric contraction. Thus, contractile activation of vascular smooth muscle is associated with a shifting pattern of substrate utilization. Exogenous acetate or octanoate can serve as the primary oxidative substrate during sustained isometric contraction.

Phosphatic metabolites, intracellular pH and free [Mg2+] in single, intact porcine carotid artery segments studied by 31P-NMR.

Superfused porcine carotid artery segments (approximately 7 cm lengths) were analyzed by 31P-NMR spectroscopic methods to characterize the 31P spectrum of arterial smooth muscle and to determine the influence of passive stretch (intraluminal pressurization, 95-100 mmHg) on cellular phosphatic metabolite levels, intracellular pH and free magnesium concentration ([Mg2+free]i). Equilibrated, single, intact arteries were studied under steady-state, constant flow conditions at 37 degrees C. Phosphoethanolamine, phosphocholine, inorganic phosphate (Pi), phosphocreatine (PCr) and nucleoside triphosphates (NTP), primarily ATP, were the principle metabolites detected in the 31P-NMR spectrum of intact arterial smooth muscle. The concentration of these metabolites and intracellular pH, as determined from the referenced chemical shift of Pi, were unaffected by pressurization. The PCr:Pi ratios determined for nonpressurized (flaccid) and pressurized arteries were 1.2 +/- 0.1 and 1.3 +/- 0.3, respectively. Intracellular pH averaged 7.02 +/- 0.02 (mean +/- 1 S.D.) for flaccid arteries vs. 7.03 +/- 0.05 for pressurized arteries. The upfield chemical shift of the beta-ATP peak, which has been described in other types of smooth muscle, was also observed in these experiments. Interestingly, pressurization significantly shifted the resonance position of this peak, which was interpreted to represent a change in [Mg2+free]i. The average [Mg2+free]i of flaccid artery preparations was computed to be 0.54 +/- 0.03 x 10(-3) M, as compared to 0.99 +/- 0.10 x 10(-3) M for pressurized arteries. This change in [Mg2+free]i was evident within the first hour following pressurization and persisted thereafter. These findings suggest that altering the resting length of vascular smooth muscle produces a change in [Mg2+free]i. This shift in free Mg2+ levels may act as a metabolic signal triggering a change in vascular smooth muscle metabolism, an effect which has been reported to occur in smooth muscle in response to stretch.

Effects of ATP reduction on the pattern of force development and myosin light chain phosphorylation in intact arterial smooth muscle.

The effect of reduction of ATP content on phosphorylation of the 20 kDa light chain of myosin (MLC) and force development in intact carotid arterial smooth muscle was investigated. With reduction of ATP to 23% of control by treatment with 2-deoxyglucose there was reduction in basal, in peak and 30 min MLC phosphorylation during contraction (P less than 0.001). The rate of force development was reduced, but maximal force was the same as control. By treatment with 50 microM iodoacetate, the resting ATP content was unchanged but fell to 22% after 30 min contraction. Basal MLC phosphorylation was the same as control, but peak (P less than 0.001) and 30 min phosphorylation were lower (P less than 0.005), even though the rate and magnitude of force development were greater. The results indicate that neither rate nor magnitude of force development correlate with MLC phosphorylation. Basal and initial MLC phosphorylation may play a cooperative role in contractile function.

Effects of altering carbohydrate metabolism on energy status and contractile function of vascular smooth muscle.

Substrate-dependent changes in vascular smooth muscle energy metabolism and contractile function were investigated in isolated porcine carotid arteries. In media containing glucose glycogen catabolism accounted for all the estimated high-energy phosphate turnover that occurred in conjunction with contraction induced by 80 mM KCl. However, in glucose-free media glycogen catabolism accounted for only a portion of the estimated ATP utilization in resting and contracting arteries, even though glycogen stores were not depleted. The glycogenolysis and lactate production that ordinarily accompanies contraction was completely inhibited by 5 mM 2-deoxyglucose (2-DG). However, there was no decrease in the high-energy phosphate levels when compared to control resting arteries similarly treated with 2-DG. The results suggest that an endogenous non-carbohydrate source may be an important substrate for energy metabolism. Treatment of arteries with 50 microM iodoacetate (IA) in media containing glucose resulted in a marked reduction of high energy phosphate levels and an accumulation of phosphorylated glycolytic intermediates, as demonstrated by 31P-NMR spectroscopy. In glucose-free media, 50 microM IA had only a slight effect on high-energy phosphate levels, while glycogenolysis proceeded unhindered. With 1 mM IA in glucose-free media, the oxidative metabolism of glycogen was inhibited as evidenced by the depletion of high-energy phosphates and the appearance of sugar phosphates in the 31P-NMR spectra. Thus, the titration of enzyme systems with IA reveals a structural partitioning of carbohydrate metabolism, as suggested by previous studies.

31P-nuclear magnetic resonance analysis of extracts of vascular smooth muscle.

31P-nuclear magnetic resonance spectroscopy was used to assess phosphate metabolites in perchloric acid extracts of rabbit aorta. In addition to the high energy phosphates, several other phosphorus compounds were detected and quantified. Most notable was the presence of a prominent phosphomonoester compound appearing at a chemical shift of 3.86 delta. This compound constituted 26% of the total extractable tissue phosphorus and is tentatively identified as ribose-5-phosphate, a pentose phosphate pathway intermediate. While ATP and phosphocreatine did not change during glucose and oxygen deprivation or during prolonged muscle contraction, the 3.86 delta phosphate decreased significantly. Furthermore, theophylline, an agent that increases intracellular cAMP, also decreased the level of the 3.86 delta phosphate. These results are consistent with the concept that intermediate metabolism sustains high energy phosphate pools in vascular smooth muscle in the steady state under various conditions. The pentose phosphate pathway may play an important role in vascular smooth muscle metabolism.

Cost and appropriateness of radionuclide exercise stress testing by cardiologists and non-cardiologists.

The hypothesis that a diagnostic evaluation performed by a generalist is less expensive than that performed by a specialist is untested. We retrospectively evaluated the indications and financial ramifications of radionuclide exercise stress testing by cardiologists and noncardiologists in 1,902 consecutive adults with normal resting electrocardiograms. Subjects completed radionuclide exercise tests for the diagnosis or management of coronary artery disease during a 14-month period. Tests were considered "indicated" or "not indicated" based on criteria determined from published reports and established practice guidelines. Savings in costs and charges were determined for a strategy of referral to a cardiologist before ordering tests. Non-cardiologists ordered more tests that were not indicated than cardiologists (69.6% vs 36.2%, chi-square = 209.07, p < 0.00001). Non-cardiologists also ordered tests that were not indicated in patients with (chi-square = 110.02, p < 0.00001) and without (chi-square = 110.02, p < 0.00001) and without (chi-square = 45.44, p < 0.00001) chest pain. Tests that were not indicated resulted in excess costs of $591,384 and excess charges of $1,082,400. Referral to a cardiologist before ordering tests could have saved $63,257 in costs and $169,800 in charges. Both cardiologists and non-cardiologists overutilized radionuclide exercise stress test; however, non-cardiologists were more likely to order tests that were not indicated. A strategy of referral to a cardiologist before ordering tests may be cost-effective in this population.

Comparison of cine magnetic resonance imaging and Doppler echocardiography for evaluation of left ventricular diastolic function.

Cine magnetic resonance (MR) imaging of the heart detected evidence of left ventricular (LV) diastolic filling abnormality in patients with LV wall thickening but normal systolic function and normal diastolic function by routine Doppler echocardiography. Cine MR imaging may be more sensitive than routine echocardiography in detecting abnormalities of LV diastolic function.

Cardiovascular actions of lead and relationship to hypertension: a review.

Chronic and acute lead poisoning cause overt, clinical symptoms of cardiac and vascular damage with potentially lethal consequences. Morphological, biochemical, and functional derangements of the heart have all been described in patients following exposure to excessive lead levels. Disturbances in cardiac electrical and mechanical activity and postmortem evidence of morphological and biochemical derangements of the myocardium have all been reported following excessive exposure to lead in humans. In addition, signs of vascular degeneration, abnormal vascular smooth muscle function, and altered vessel compliance have been described in humans chronically and acutely exposed to toxic lead levels. Similar cardiovascular complications have been detected following excessive lead exposure in experimental animals. Myocarditis, electrocardiographic disturbances, heightened catecholamine arrhythmogenicity, altered myocardial contractile responsiveness to inotropic stimulation, degenerative structural and biochemical changes affecting the musculature of the heart and vasculature, hypertension, hypercholesterolemia, atherosclerosis, and increased vascular reactivity to alpha-adrenergic agonists have been among the reported cardiovascular disturbances linked to lead poisoning. Less certain are the cardiovascular effects of subclinical lead poisoning. Although controversial, chronic low-level lead exposure has been linked to hypertension and other cardiovascular disturbances in both clinical and experimental studies. In general, it can be concluded that lead over a wide range of exposure intensities can induce significant changes in the function of the cardiovascular system. Evidence points to the involvement of multiple sites of action. Cardiac and vascular sites, as well as sites within the central nervous system, have all been implicated in the sequelae of cardiovascular effects. The exact pathogenic mechanisms that underlie the actions of lead in the cardiovascular system, however, have yet to be elucidated definitively.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin converting enzyme inhibitors in bone marrow transplant recipients with depressed left ventricular function.

Pre-existing left ventricular dysfunction in patients undergoing induction therapy with cyclophosphamide prior to bone marrow transplantation (BMT) has resulted in overt heart failure in a large number of patients. This fact excludes the majority of such patients from consideration for BMT at many centers. We sought to determine if prophylactic treatment with the angiotensin converting enzyme inhibitor enalapril prevents this deterioration in pre-existing left ventricular dysfunction. We treated six consecutive patients with initial left ventricular ejection fractions (LVEF) by radionuclide gated blood pool imaging (RGBP) of < 50% (42 +/- 7%) with enalapril 5 mg orally twice per day started 48 h prior to induction therapy and continued throughout the follow-up period. Serial RGBP imaging demonstrated an increase in LVEF in all patients to 54 +/- 6% (P < 0.005). No patient experienced clinical deterioration during a follow-up period of 18 +/- 11 months. We conclude that prophylactic treatment with enalapril may prevent deterioration in pre-existing mild left ventricular dysfunction during BMT.

Semiautomatic evaluation of left ventricular diastolic function with cine magnetic resonance imaging.

RATIONALE AND OBJECTIVES: Cine magnetic resonance (MR) imaging is a relatively new technique that can be used to study cardiac function with high spatial and temporal resolution. However, detailed functional analysis of the entire cardiac cycle with cine MR imaging is time consuming and labor intensive. We analyzed diastolic function using a semiautomatic routine that reduces the time necessary for analysis. METHODS: Twenty subjects (10 normal control subjects and 10 patients with isolated diastolic dysfunction) were examined. Short-axis cine MR images were obtained at 32 phases of the cardiac cycle. A semiautomatic boundary-finding routine was used to determine left ventricular (LV) volumes at each phase. Volume-versus-time and first-derivative curves were created from these data. Several parameters derived from the MR imaging curves were used to characterize diastole. RESULTS: Two parameters--the ratio of early peak filling rate to late peak filling rate and the percentage of filling during early diastole--perfectly distinguished subjects with LV diastolic dysfunction from the normal control subjects. The semiautomatic analysis method substantially reduced the time necessary for analyzing the MR imaging data, compared with manual analysis. CONCLUSION: Cine MR imaging, especially with time-saving techniques such as our service automatic analysis method, has promise as a research and clinical tool in evaluating LV diastolic function.

Association of ventricular ectopy with nuclear scintigraphic perfusion defects during dipyridamole stress testing.

BACKGROUND AND HYPOTHESIS: No information is available regarding the significance of ventricular ectopic activity induced during dipyridamole nuclear scintigraphic stress testing. This study tested the hypothesis that dipyridamole-induced ventricular ectopy predicts a thallium-201 or technetium-99m sestamibi perfusion defect. METHODS: A group of 186 consecutive patients with premature ventricular contractions and/or couplets occurring during dipyridamole stress testing (ventricular tachycardia did not occur) was compared with a control group of 194 patients without ventricular ectopy during dipyridamole stress testing. RESULTS: The results indicated that ventricular ectopy induced during dipyridamole infusion occurred more frequently in patients demonstrating either a fixed or reversible perfusion defect on scintigraphic imaging (p < 0.01). The higher frequency of perfusion defects in this group of patients was attributable to a higher frequency of "fixed" compared with "reversible" defects (p < 0.05). This finding is consistent with the additional observation that ventricular ectopy induced by dipyridamole was associated with the presence of Q waves on the resting ECG (p < 0.05). The positive and negative predictive values of the presence of ventricular ectopy in predicting a fixed myocardial perfusion defect were 59 and 54%, respectively. CONCLUSIONS: Ventricular ectopy induced during dipyridamole infusion suggests the presence of a fixed myocardial perfusion defect.

Comparison of auscultation with two-dimensional and Doppler echocardiography in patients with suspected mitral valve prolapse.

Auscultation was compared to two-dimensional echocardiography (2D echo) and Doppler ultrasonography in 140 consecutive patients referred for evaluation for suspected mitral valve prolapse (MVP) to asses the precision of the two diagnostic methods. Ninety patients (64%) had midsystolic clicks, of which 42 (47%) had MVP by echocardiography; 6 patients (4%) had MVP by 2D echo but no click on examination. In 15 (17%) of the 90 patients, a click was heard only in the standing or squatting positions and 2D echo did not detect prolapse in the supine position in 10 (67%) of the 15. With auscultation as the reference standard for MVP, 2D echo has a sensitivity of 47% and a specificity of 89%. Of the 140 patients, 51 (36%) had systolic murmurs; Doppler detected mitral and/or tricuspid regurgitation in 26 (50%). In 23 (16%) patients, there was Doppler evidence of mitral or tricuspid regurgitation even though systolic murmurs were not heard. Auscultation shows a 53% sensitivity and 73% specificity for systolic murmurs, using Doppler ultrasonography as the reference standard. Of 48 patients with MVP by 2D echo, 15 (13%) had associated mitral regurgitation by Doppler. The results indicate that 2D echo and Doppler ultrasonography should be interpreted in concert with auscultation for the diagnosis of mitral valve prolapse and for therapeutic decision making.

How well does radionuclide dipyridamole stress testing detect three-vessel coronary artery disease and ischemia in the region supplied by the most stenotic vessel?

PURPOSE: This study was done to evaluate the accuracy of radionuclide dipyridamole stress imaging to detect multivessel disease and ischemia in segments of myocardium supplied by the most stenotic vessel. METHODS: A retrospective analysis of consecutive patients with known triple-vessel disease of at least 50% stenosis in each of the three major epicardial coronary arteries who had exercise (n=44) or dipyridamole (n=86) stress testing, or both, within 6 months of coronary angiography. RESULTS: The accuracy of dipyridamole stress testing to detect three-vessel disease was 52% and ischemia was detected in the region supplied by the most stenotic vessel in 67% of patients. The sensitivity and specificity rates of radionuclide imaging to detect ischemia in the region supplied by the vessel of tightest stenosis were 69% and 74% for the left anterior descending coronary artery (LAD), 61% and 78% for the right coronary artery (RCA), and 61% and 57% for the left circumflex coronary artery (LCX). Based on these values, in 39% of patients in whom the RCA or LCX was the most stenotic vessel and in 31% of patients in whom the LAD was the most stenotic vessel, perfusion defects were not present on their nuclear scans. CONCLUSIONS: These results have important implications for interventional cardiologists who perform angioplasty on the most stenotic vessel, because the regions supplied by these vessels may not be the most ischemic. Furthermore, dipyridamole stress imaging may significantly underestimate the number of patients with substantial three-vessel coronary artery disease when qualitative imaging is done.