Calcium-dependent threonine phosphorylation of nonmuscle myosin in stimulated RBL-2H3 mast cells.

Stimulation of RBL-2H3 m1 mast cells through the IgE receptor with antigen, or through a G protein-coupled receptor with carbachol, leads to the rapid appearance of phosphothreonine in nonmuscle myosin heavy chain II-A (NMHC-IIA). We demonstrate that this results from phosphorylation of Thr-1940 by calcium/calmodulin-dependent protein kinase II (CaM kinase II), activated by increased intracellular calcium. The phosphorylation site in rodent NMHC-IIA was localized to the carboxyl terminus of NMHC-IIA distal to the coiled-coil region, and identified as Thr-1940 by site-directed mutagenesis. A fusion protein containing the NMHC-IIA carboxyl terminus was phosphorylated by CaM kinase II in vitro, while mutation of Thr-1940 to Ala eliminated phosphorylation. In contrast to rodents, in humans Thr-1940 is replaced by Ala, and human NMHC-IIA fusion protein was not phosphorylated by CaM kinase II unless Ala-1940 was mutated to Thr. Similarly, co-transfected Ala --> Thr-1940 human NMHC-IIA was phosphorylated by activated CaM kinase II in HeLa cells, while wild type was not. In RBL-2H3 m1 cells, inhibition of CaM kinase II decreased Thr-1940 phosphorylation, and inhibited release of the secretory granule marker hexosaminidase in response to carbachol but not to antigen. These data indicate a role for CaM kinase stimulation and resultant threonine phosphorylation of NMHC-IIA in RBL-2H3 m1 cell activation.

Glucose metabolism in reperfused myocardium measured by [2-18F] 2-fluorodeoxyglucose and PET.

OBJECTIVE: [2-18F] 2-fluorodeoxyglucose (FDG) is widely used to trace glucose metabolism for cardiac imaging with positron emission tomography. Because the transport and phosphorylation rates differ for glucose and FDG, a lumped constant (LC) is used to correct for these differences. The effects of ischemia and reperfusion on the LC in vivo are unknown. To determine the validity of FDG as a tracer of glucose metabolism in post-ischemic myocardium in vivo, the relationship between glucose uptake (GU) and FDG metabolic rate (FDG-MR) was assessed early post-reperfusion following a transient ischemic event. METHODS: FDG metabolic rate, measured with FDG and PET, was compared to invasive measurements of substrate metabolism in reperfused and global myocardium of dogs subjected to 25 min ischemia and 2 h reperfusion. RESULTS: The FDG metabolic rate was decreased 20 +/- 4% in reperfused relative to remote myocardium. Glucose oxidation and lactate uptake were also decreased in reperfused relative to global myocardium, by 26 +/- 6% and 60 +/- 8% respectively. Glucose uptake did not differ significantly between reperfused and global myocardium. A linear correlation between FDG metabolic rate and glucose uptake was found in both reperfused and remote myocardium. Estimates of the LC from the slopes of the regression lines were similar in reperfused and remote myocardium, 1.25 and 1.44 respectively, and did not differ significantly from the LC determined in control dogs, 1.1. CONCLUSIONS: We conclude that the FDG metabolic rate continues to correlate well with glucose metabolism in reperfused myocardium. While FDG metabolic rate was modestly decreased in the absence of a significant change in glucose uptake, large alterations in the LC are not found 2 h post-reperfusion in vivo.

Trimetazidine-induced enhancement of myocardial glucose utilization in normal and ischemic myocardial tissue: an evaluation by positron emission tomography.

Trimetazidine has an anti-ischemic effect in angina pectoris. This agent has no hemodynamic effects, and its benefit is presumed to be based on a metabolic mechanism of action. A group of 33 dogs undergoing openchest left anterior descending coronary artery (LAD) ligation causing prolonged ischemia were imaged with quantitative positron emission tomography (PET) using 2-[18F]fluoro-2-deoxy-D-glucose (18FDG) to measure regional glucose metabolic utilization (rGMU) and [11C]acetate to measure regional monoexponential washout rate constant (Kmono) for oxidative metabolism in nonrisk and ischemic-risk myocardium. A total of 20 dogs were pretreated with trimetazidine at low dose (n = 10, 1 mg/kg) and high dose (n = 10, 5 mg/kg) and compared with 13 control dogs. Microsphere-measured myocardial blood flow (mL/min/g) was measured preocclusion and repeated hourly after occlusion and expressed as a ratio of preocclusion myocardial blood flow to verify a stable level of ischemia during PET. No differences were seen in postocclusion ischemic risk/nonrisk myocardial blood flow between treatment groups (p = not significant [NS]). Preocclusion and hourly measurements of heart rate and blood pressure corrected for baseline revealed no difference in control dogs versus trimetazidine (low-dose and high-dose) groups (p = NS). 18FDG-derived rGMU (micromol/min/g) was increased in high-dose trimetazidine versus control dogs in nonrisk and ischemic risk groups, respectively (1.16+/-0.57 vs 0.51+/-0.38 and 0.43+/-0.29 vs 0.20+/-0.14; p <0.05). rGMU was increased proportionately in nonrisk and ischemic risk in all groups without significant differences when corrected for nonrisk rGMU (ischemic risk/nonrisk was 0.92+/-1.3 vs 0.64+/-0.66 vs 0.40+/-0.22 for control dogs, all trimetazidine and high-dose trimetazidine groups). Kmono (min(-1) was not altered in any group (nonrisk = 0.13+/-0.03 vs 0.13+/-0.03 vs 0.14+/-0.02 and ischemic risk = 0.18+/-0.05 vs 0.17+/-0.06 vs 0.16+/-0.06 for control dogs, all trimetazidine and high-dose trimetazidine groups, respectively; p = NS for nonrisk vs ischemic risk, between and within groups). Our data verify that trimetazidine does not alter hemodynamic porameters. It increases total glucose utilization (oxidative and glycolytic) in myocardium without preferential increase in ischemic tissue. Absence of change in total oxidative metabolism suggests increased glucose metabolism is predominantly glycolysis or an increase in glucose oxidation with similar decrease in fatty acid oxidation.

Regulation of pyruvate dehydrogenase activity and glucose metabolism in post-ischaemic myocardium.

Pyruvate dehydrogenase (PDH) is regulated both by covalent modification and through modulation of the active enzyme by metabolites. In the isolated heart, post-ischaemic inhibition of PDH, leading to uncoupling of glycolysis and glucose oxidation and a decrease in cardiac efficiency, has been described. In vivo, post-ischaemic reperfusion leads to metabolic abnormalities consistent with PDH inhibition, but the effects of ischaemia/reperfusion on PDH are not well characterized. We therefore investigated PDH regulation following transient ischaemia in vivo. In 33 open-chest dogs, the left anterior descending (LAD) was occluded for 20 min followed by 4 h reperfusion. In 17 dogs, dichloroacetate (DCA) was injected prior to reperfusion, while 16 dogs served as controls. In dogs without DCA, glucose oxidation and lactate uptake were lower in reperfused than in remote tissue, suggesting reduced flux through PDH. However, percent active and total PDH measured in myocardial biopsies were similar in both territories, excluding covalent enzyme modification or loss of functional enzyme. DCA activated PDH activity similarly in both regions and abolished differences in glucose oxidation and lactate uptake. Thus, decreased PDH flux in reperfused myocardium does not result from covalent modification or loss of total enzyme activity, but more likely from metabolite inhibition of the active enzyme. DCA leads to essentially complete activation of PDH, increases overall glucose utilization and abolishes post-ischaemic inhibition of glucose oxidation.

Simultaneous measurement of myocardial oxygen consumption and blood flow using [1-carbon-11]acetate.

UNLABELLED: [1-Carbon-11]acetate has been used as a tracer for oxidative metabolism with PET. The aim of this study was to validate, in humans, a previously proposed two-compartment model for [1-11C]acetate for the noninvasive measurement of myocardial oxygen consumption (MVO2) and myocardial blood flow (MBF) with PET. METHODS: Twelve healthy volunteers were studied with [13N]ammonia, [1-11C]acetate and PET. Myocardial oxygen consumption was invasively determined by the Fick method from arterial and coronary sinus O2 concentrations and from MBF obtained by [13N]ammonia PET. RESULTS: Directly measured MVO2 ranged from 5.2 to 11.1 ml/100g/min, and MBF ranged from 0.48 to 0.88 ml/g/min. Oxidative flux through the tricarboxylic acid cycle, reflected by the rate constant k2, which correlated linearly with measured MVO2 [k2 = 0.0071 + 0.0074(MVO2); r = 0.74, s.e.e. = 0.015]. With this correlation, MVO2 could be estimated from the model-derived k2 value by MVO2 = 135(k2) - 0.96. The slope of this relationship was close to that previously obtained in rats and implies that the tricarboxylic acid cycle intermediate metabolite pool sizes are comparable. The net extraction (K1) of [1-11C]acetate, measured by PET, from blood into myocardium correlated closely with MBF by K1 = 0.15 + 0.73(MBF) (r = 0.93, s.e.e. = 0.033) and, thus, provided noninvasively obtainable measures of blood flow. CONCLUSION: The proposed compartment model for [1-11C]acetate fits the measured kinetics well and, with proper calibration, allows estimation of absolute MVO2 rather than only an index of oxidative metabolism. Furthermore, [1-11C]acetate-derived estimates of MBF are feasible.

Compartment model for measuring myocardial oxygen consumption using [1-11C]acetate.

UNLABELLED: Although [1-11C]acetate has been validated as a PET tracer for myocardial oxygen consumption (MVO2) in animals and humans, mono- and biexponential fitting of the tissue time-activity curve yields only estimates of MVO2. This study attempts to develop and validate a simple tracer kinetic model in vivo for estimation of regional MVO2. METHODS: Twenty-seven experiments were performed in 12 anesthetized dogs with [1-11C]acetate and serial PET images under different MBF and MVO2 (baseline, ischemia, xylazine, dobutamine and dipyridamole). Estimates of MVO2 were obtained from dynamic [1-11C]acetate PET and model fitting. MBF was measured by radiolabeled microspheres, and MVO2 was calculated by the Fick method using arterial and coronary blood samples. RESULTS: The proposed model fitted equally well for all study conditions with a multiple correlation coefficient of 0.985 +/- 0.026. Estimated MVO2 correlated linearly with measured MVO2 (y = 0.033 + 0.690x, r = 0.92, s.e. of estimates = 0.020). CONCLUSION: This study indicates that MVO2 can be assessed with PET and [1-11C]acetate over a wide range with a simple tracer kinetic model.

Inhibition of glyceraldehyde-3-phosphate dehydrogenase in post-ischaemic myocardium.

OBJECTIVE: Myocardial reperfusion following brief period of ischaemic is associated with prolonged, reversible periods of metabolic dysfunction. As the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is inhibited in vitro by reactive oxygen species, we hypothesized that production of reactive oxygen species during reperfusion would lead to inhibition of GAPDH in post-ischaemic myocardium. METHODS: Anaesthetized closed-chest-dogs were subjected to 20 min balloon occlusion of the left anterior descending coronary artery. Biopsy samples were taken after 3 and 24 h of reperfusion, to determine the activity of GAPDH and the concentrations of glycolytic intermediates in post-ischaemic and remote, non-ischaemic territories. RESULTS: A significant reduction in GAPDH activity was observed in post-ischaemic relative to remote tissue after 3 h reperfusion (4.8 +/- 0.5 vs. 2.9 +/- 0.2 mumol/min/mg protein; P < 0.01). Western blotting revealed no reduction in the levels of GAPDH protein. Analysis of enzyme kinetics showed the loss of activity to be associated with decreased Vmax (5.9 +/- 0.5 vs. 3.2 +/- 0.2 mumol/min/mg protein; P < 0.01) with no significant change in the Km for glyceraldehyde-3-phosphate (GAP). Incubation of the inhibited enzyme under both mild and strong reducing conditions failed to reactivate the enzyme. The acute reduction in enzyme activity in post-ischaemic tissue was accompanied by regional differences in glycolytic intermediates, notably a twofold accumulation of GAP (P < 0.05), and a reduction in the glucose metabolic rate (GMR) determined by positron emission tomography and [18F]2-fluorodeoxyglucose. By 24 h reperfusion, no regional differences in GAPDH activity, reaction Vmax or Km, GAP concentrations or GMR were detectable. CONCLUSIONS: These results suggest that inhibition of GAPDH activity may represent an important point at which glycolysis is limited during reperfusion, and further, that the mechanisms of enzyme inhibition do not involve simple oxidation or S-thiolation of critical active site thiol groups.

Stimulation of c-Jun kinase and mitogen-activated protein kinase by ischemia and reperfusion in the perfused rat heart.

Ischemia and reperfusion lead to the rapid induction of proto-oncogenes in the heart and subsequent induction of genes with cardioprotective functions. The activity of the transcription factors c-Jun and ATF-2 can be stimulated by activation of c-Jun amino-terminal kinase (JNK) in response to a variety of stresses. Here we show that ischemia and reperfusion led to the activation of JNK and also of the distantly-related mitogen activated protein kinase (MAPK). Activation of JNK, but not (MAPK), was abolished by removal of calcium from the perfusate immediately prior to ischemia. In contrast, infusion of the hydrogen peroxide scavenger catalase abolished activation of MAPK in response to ischemia and reperfusion, but activation of JNK was inhibited significantly by catalase only when superoxide dismutase was also present. Hydrogen peroxide infusion activated MAPK but not JNK, supporting a role for hydrogen peroxide produced during reperfusion in MAPK activation. We conclude that while ischemia and reperfusion activate both JNK and MAPK, the mechanisms of activation are different for the 2 kinases. Activation of these kinases is likely to contribute to altered gene expression in response to ischemia and reperfusion.

Quantification of myocardial blood flow using dynamic nitrogen-13-ammonia PET studies and factor analysis of dynamic structures.

UNLABELLED: In this study, factor analysis of dynamic structures (FADS) was used to extract the "pure" blood-pool time-activity curves (TACs) and to generate parametric myocardial blood flow (MBF) images (pixel unit: ml/min/g). METHODS: Ten dynamic 13N-ammonia dog PET studies (three baseline, five hyperemia and two occlusion) were included. Three factors (TACs) and their corresponding factor images (the right ventricular and left ventricular blood pools and myocardial activities) were extracted from each study. The left ventricular factors matched well with the plasma TACs. The factor images of myocardium were then converted to a parametric images of MBF using a relationship derived from a two-compartment model. RESULTS: MBF estimates obtained from FADS correlated well with MBF estimates obtained with the two-compartment model (r = 0.98, slope = 0.84) and microsphere techniques (r = 0.96, slope = 0.94). FADS-generated MBF parametric images have better image quality and lower noise levels compared to those generated with Patlak graphical analysis. CONCLUSION: Regional MBF can be measured accurately and noninvasively with 13N-ammonia dynamic PET imaging and FADS. The method is simple, accurate and produces parametric images of MBF without requiring blood sampling and spillover correction.

Effect of exercise supplementation during adenosine infusion on hyperemic blood flow and flow reserve.

Physical stress might modulate myocardial blood flow in near-maximally dilated coronary arteries by increasing coronary perfusion pressure, myocardial contractility, and heart rate. The net effect of these changes on hyperemic blood flows has not yet been defined in humans. To quantify the effect of physical exercise on pharmacologically induced hyperemia, myocardial blood flow was measured in 11 healthy volunteers. Measurements were performed with positron emission tomographic imaging with nitrogen-13 ammonia at rest, during intravenous (i.v.) adenosine administration (140 micrograms.kg-1.min-1 over 6 minutes), and during i.v. adenosine administration plus supine bicycle exercise with a maximal workload of 125 W. Myocardial blood flow was quantified by using a previously validated graphic analysis. Heart rate, systolic blood pressure, rate-pressure product, and mean aortic blood pressures were significantly higher during combined physical and pharmacologic stress than during pharmacologic stress alone. However, myocardial blood flow decreased from 2.6 +/- 0.4 to 2.2 +/- 0.4 ml.min-1.gm-1 with the addition of physical stress (p < 0.05). This decline was associated with a significant increase in coronary vascular resistance (35 +/- 6 vs 52 +/- 13 mm Hg.ml-1.gm.min; p < 0.05). Accordingly, myocardial flow reserve declined, from 5.0 +/- 0.9 to 4.3 +/- 1.0, with exercise supplementation (p < 0.05). Exercise in addition to pharmacologic stress increases coronary vascular resistance and thus significantly decreases hyperemic myocardial blood flow and flow reserve. This decrease results most likely from an increase in extravascular restrictive forces caused by higher ventricular pressures and contractility during physical stress.

Responses of blood flow, oxygen consumption, and contractile function to inotropic stimulation in stunned canine myocardium.

To examine the effects of inotropic stimulation on regional myocardial blood flow (MBF), oxidative metabolism, and contractile function in stunned myocardium, nine closed-chest dogs were studied 2 hours postreperfusion after a 25 minute occlusion of the left anterior descending coronary artery (LAD). MBF was determined with microspheres, and regional myocardial oxygen consumption (MVO2) was estimated from the rate constant k1 of the rapid clearance phase of [1-11C] acetate time activity curves, recorded with dynamic positron emission tomography. Myocardium at risk was determined from [13N] ammonia images obtained during occlusion. Wall motion, assessed by two-dimensional echocardiography, was impaired in postischemic myocardium in all dogs 2 hours after reperfusion. Dobutamine infusion increased the rate pressure product by 70% +/- 31% and significantly improved contractile function in the postischemic region in all dogs. In remote myocardium, MVO2 increased from 5.7 +/- 1.2 to 8.6 +/- 1.6 mumol/gm/min, and blood flow from 0.87 +/- 0.16 to 1.52 +/- 0.42 ml/gm/min in response to dobutamine. In reperfused myocardium, MVO2 increased from 3.1 +/- 0.7 to 7.4 +/- 1.5 mumol/gm/min, and blood flow from 0.51 +/- 0.12 to 1.2 +/- 0.4 ml/gm/min. Oxygen extraction increased significantly in reperfused myocardium relative to remote myocardium consistent with a flow-limited response to dobutamine stimulation. The improvement in contractile function failed to correlate significantly with relative increases in MBF or MVO2, suggesting that mechanical function is not as tightly coupled as MBF and MVO2 in postischemic myocardium during inotropic stimulation.

Validation of a model for [1-11C]acetate as a tracer of cardiac oxidative metabolism.

To develop a compartmental model for estimating myocardial oxygen consumption rate (MVO2) with [1-11C]acetate, the metabolic fate of radiolabeled acetate was determined in normoxic and ischemic conditions in isolated perfused rat hearts. Glutamate composed 63 +/- 1 and 44 +/- 7% of the total tissue radioactivity 2 min postinjection in normoxic and ischemic myocardium, respectively, and radiolabeled glutamate remained the largest fraction throughout 40 min of perfusion. Based on the biochemical pathway of the tracer and the temporal distribution of 14C-labeled metabolites, a six-compartment model was formulated. Studies using [1-11C]acetate and a pair of NaI detectors were then performed in the same perfused heart system to validate the model. Consistency between the model predictions and biochemical measurements of tissue and effluent metabolites supported the validity of the kinetic model in normoxic and ischemic conditions. Model-estimated MVO2 correlated well with experimentally measured MVO2 for normoxic, hypoxic, and ischemic conditions, with a slope of 0.97 (r = 0.95). In addition, the model-estimated rate constant, k42, which corresponded to the oxidative flux, correlated strongly with the myocardial clearance rate (k1 or kmono) determined from the tissue kinetics. These findings provide a mechanistic basis for the use of k1 or kmono as an index of MVO2 in both normoxic and ischemic myocardium studied with [1-11C]acetate and positron emission tomography.

A refined method for quantification of myocardial oxygen consumption rate using mean transit time with carbon-11-acetate and dynamic PET.

The utility of the mean transit time equation was investigated for estimation of the myocardial clearance rate constant of 11C-acetate, which is proportional to myocardial oxygen consumption rates. The mean transit time approach was also employed to generate parametric images of the clearance rate constant of 11C-acetate with dynamic PET imaging in 20 normal human studies. Input function delays and cutoff errors due to the truncation of the myocardial tissue time-activity curve at a finite time were corrected. The clearance rate constants estimated by mean transit time correlated well with the estimates by conventional monoexponential fitting (15 min (truncation time): Y = 0.01 + 0.94X, correlated coefficient (r) = 0.99; 16 min: Y = 0.03 + 0.94X, r = 0.98; 20 min: Y = 0.03 + 0.84X, r = 0.99). The clearance rate constants estimated by the mean transit time approach also correlated well (r = 0.94) with the measured rate-pressure products. The quality and noise level of parametric images of the clearance rate constants generated by mean transit time are improved over those generated by monoexponential fitting. Additional advantages of the mean transit time approach compared to the standard monoexponential fitting method for estimating myocardial clearance rate constant of 11C-acetate include ease of input function delay correction, less sensitivity to the shape of the input function and elimination of subjective data selection of the linear portion of the clearance data on a semilog plot. Thus, this approach is expected to facilitate objective quantitative analysis of indices of myocardial oxygen consumption.

Quantification and parametric imaging of renal cortical blood flow in vivo based on Patlak graphical analysis.

Patlak graphical analysis was applied to quantify renal cortical blood flow with N-13 ammonia and dynamic positron emission tomography. Measurements were made in a swine model of kidney transplantation with a wide range of normal and abnormal renal blood flows (N = 57 studies) and in 20 healthy human volunteers (N = 45 studies). Estimates of renal cortical blood flow by the Patlak method were compared to those from a two-compartment model for N-13 ammonia. In addition, estimates of renal cortical blood flow by the N-13 ammonia PET approach were compared in 10 normal human volunteers to estimates by the metabolically inert, freely diffusible O-15 water and a one-compartment model. Patlak graphical analysis estimates of renal cortical blood flow correlated linearly with the standard two-compartment model in pigs (y = -0.05 + 1.01x, r = 0.99) and in humans (y = 0.57 + 0.88x, r = 0.93). Estimates of renal cortical blood flow by O-15 water in human volunteers were also linearly correlated with those by N-13 ammonia and the Patlak graphical analysis (y = 0.71 + 0.84x, r = 0.86). Renal cortical blood flow estimates were highly reproducible both with N-13 ammonia and O-15 water measurements in humans. It is concluded that the Patlak graphical analysis with N-13 ammonia dynamic positron emission tomograpic imaging renders accurate and reproducible estimates of renal cortical blood flow. Moreover, the graphical analysis approach is 1,000 times faster than the standard model fitting approach and suitable for generating parametric images of renal blood flow in the clinical setting.

Metabolism in non-ischemic myocardium during coronary artery occlusion and reperfusion.

Blood flow and metabolism in non-ischemic myocardium were studied at baseline and during occlusion and reperfusion of the left anterior descending coronary artery in closed chest dogs using positron emission tomography. Myocardial blood flow (MBF) and oxygen consumption (MVO2) in non-ischemic tissue were each increased by 28% relative to the rate pressure product during occlusion, consistent with increased work to compensate for the dyskinetic segment. MVO2 in non-ischemic sectors remained elevated relative to the rate pressure product early (1-2 h) post-reperfusion, 21% above baseline, but subsequently normalized. When sectors with normal blood flow during occlusion were divided into sectors adjacent to and remote from the risk zone, MBF in the 2 sector groups was similar at all times, but metabolic differences were found. MVO2 was depressed by 15% in adjacent relative to remote sectors 1 day post-reperfusion, with a concomitant 62% increase in glucose metabolic rate; relative increases in glucose metabolism were found only when glucose metabolism was low in remote myocardium, suggesting a decreased suppressibility of glucose metabolism in adjacent myocardium. The kinetics of (1-11C] palmitate were also altered in adjacent sectors, consistent with a small increase in esterification relative to oxidation of long chain fatty acids. Thus, sectors adjacent to ischemic segments show metabolic changes similar to those seen in reversibly injured post-ischemic tissue, despite normal blood flow during occlusion.

Glycogenolytic and haemodynamic responses to bovine serum albumin in isolated perfused livers from sensitized rats.

Infusion of BSA into isolated perfused livers of rats sensitized by intraperitoneal injection of BSA led to rapid increases in portal-vein pressure, glucose output and the lactate/pyruvate ratio in the effluent perfusate, with concomitant decreases in oxygen consumption and lactate+pyruvate efflux. The responses were attenuated at low (approximately 7 microM) perfusate Ca2+, but were restored on re-addition of normal Ca2+ concentration. Co-infusion of the cyclo-oxygenase inhibitor ibuprofen (50 microM) or of the platelet-activating factor receptor antagonist WEB 2170 (1.2 microM) inhibited haemodynamic responses to BSA (5 micrograms/ml) by 48% and 59% respectively. Responses to BSA were also attenuated by prior infusion of the beta-adrenergic agonist isoprenaline. Glycogen phosphorylase a activity was increased by 26% in livers freeze-clamped 2 min after onset of BSA infusion; tissue prostaglandin E2 content was increased at 2 min, but returned to control levels at 5 min. Homologous desensitization of hepatic responses to BSA was observed, but heterologous desensitization with heat-aggregated IgG did not take place. It is concluded that livers from rats sensitized to antigen respond directly to subsequent antigen administration by vasoconstriction and glycogenolysis, and that autacoid mediators are involved in these responses.

Factors affecting myocardial 2-[F-18]fluoro-2-deoxy-D-glucose uptake in positron emission tomography studies of normal humans.

The goal of this study was to identify the anatomic and physiologic factors affecting left ventricular myocardial 2-[F-18]fluoro-2-deoxy-D-glucose (FDG) uptake and myocardial glucose utilization rates (MRGlc) in normal humans. Eighteen healthy male volunteers were studied in the fasting state (4-19 h) and 16 after oral glucose loading (100 g dextrose) with positron emission tomography (PET) and FDG. Substrate and hormone concentrations were measured in each study. The kinetics of myocardial FDG uptake were evaluated using both a three-compartment model and Patlak graphical analysis. Systolic blood pressures and rate pressure products were similar in the fasting and postglucose states. MRGlc averaged 0.24 +/- 0.17 mumol/min/g in fasting subjects and rose to 0.69 +/- 0.11 mumol/min/g after glucose loading. Phosphorylation rate constant, k3, and MRGlc were linearly related (P < 0.001). Increases in MRGlc following glucose loading were correlated with plasma glucose, insulin and free fatty acid concentrations, ratios of insulin to glucagon levels, and influx rate constants of FDG. Glucose loading improved the diagnostic image quality due to more rapid clearance of tracer from blood and higher myocardial FDG uptake. When MRGlc, glucose and insulin concentrations, and insulin to glucagon ratios exceeded 0.2 mumol/min/g, 100 mg/dl, 19 microU/ml, and 0.2 microU/pg, respectively, myocardial uptake of FDG was always adequate for diagnostic use. FDG image quality and MRGlc were similar after relatively short (6 +/- 2 h) and overnight (16 +/- 2 h) fasting. Significant (P < 0.05) regional heterogeneity of myocardial FDG uptake and MRGlc was observed in both the fasting and the postglucose studies. MRGlc and FDG uptake values in the posterolateral wall were higher than those in the anterior wall and septum. Thus, both 6-h and overnight fasts resulted in similarly low myocardial glucose utilization rates. While MRGlc and myocardial FDG uptake depended on plasma glucose, free fatty acid, and insulin concentrations, the results also suggest an additional dependency on plasma glucagon levels. Regional heterogeneities in myocardial FDG uptake and MRGlc are evident and independent of the subjects' dietary state. These regional heterogeneities need to be considered in studies of patients with cardiac disease.