Cardiac endothelial transport and metabolism of adenosine and inosine.

The influence of transmembrane flux limitations on cellular metabolism of purine nucleosides was assessed in whole organ studies. Transcapillary transport of the purine nucleosides adenosine (Ado) and inosine (Ino) via paracellular diffusion through interendothelial clefts in parallel with carrier-mediated transendothelial fluxes was studied in isolated, Krebs-Henseleit-perfused rabbit and guinea pig hearts. After injection into coronary inflow, multiple-indicator dilution curves were obtained from coronary outflow for 90 s for 131I-labeled albumin (intravascular reference tracer), [3H]arabinofuranosyl hypoxanthine (AraH; extracellular reference tracer and nonreactive adenosine analog), and either [14C]Ado or [14C]Ino. Ado or Ino was separated from their degradative products, hypoxanthine, xanthine, and uric acid, in each outflow sample by HPLC and radioisotope counting. Ado and Ino, but not AraH, permeate the luminal membrane of endothelial cells via a saturable transporter with permeability-surface area product PS(ecl) and also diffuse passively through interendothelial clefts with the same conductance (PSg) as AraH. These parallel conductances were estimated via fitting with an axially distributed, multi-pathway, four-region blood-tissue exchange model. PSg for AraH were approximately 4 and 2.5 ml. g(-1). min(-1) in rabbits and guinea pigs, respectively. In contrast, transplasmalemmal conductances (endothelial PS(ecl)) were approximately 0.2 ml. g(-1). min(-1) for both Ado and Ino in rabbit hearts but approximately 2 ml. g(-1). min(-1) in guinea pig hearts, an order of magnitude different. Purine nucleoside metabolism also differs between guinea pig and rabbit cardiac endothelium. In guinea pig heart, 50% of the tracer Ado bolus was retained, 35% was washed out as Ado, and 15% was lost as effluent metabolites; 25% of Ino was retained, 50% washed out, and 25% was lost as metabolites. In rabbit heart, 45% of Ado was retained and 5% lost as metabolites, and 7% of Ino was retained and 3% lost as metabolites. We conclude that endothelial transport of Ado and Ino is a prime determinant of their metabolic fates: where transport rates are high, metabolic transformation is high.

A collaborative project in Connecticut to improve the care of patients with acute myocardial infarction.

BACKGROUND: State-based peer review organizations (PROs) and individual hospitals are challenged to achieve their quality improvement (QI) goals with shrinking resources. In 1993-1994 the Connecticut PRO and 15 local hospitals generated a comparative QI database on acute myocardial infarction (AMI) care for 1,202 Medicare and non-Medicare patients discharged in 1992 and 1993. METHODS: A steering committee composed of hospital and PRO representatives was assembled to provide oversight. PRO staff developed a chart abstraction tool and trained hospital abstracters who collected and submitted data to the PRO for comparative analyses. Written feedback was provided to all hospitals and supplemented with onsite presentations when requested. Each hospital prepared a written QI plan based on its unique data profile. RESULTS: Opportunities for improvement were identified at all hospitals. The most commonly targeted areas for improvement included the use of thrombolytics at presentation, aspirin at presentation and at discharge, and beta blockers at discharge. Improvement interventions included staff education sessions, development of AMI critical paths and standing orders, and storage of appropriate medications in emergency departments. Self-report data from the hospitals indicate improvements in care. DISCUSSION: PROs and hospitals can augment their individual QI activities by working together to share data, resources, and lessons learned. Twenty-three hospitals are now collaborating with the Connecticut PRO on a similarly designed QI project aimed at improving the care of patients hospitalized with atrial fibrillation. This project includes a more formal means of communicating QI interventions.

A collaborative project in Connecticut to improve the care of patients with acute myocardial infarction.

BACKGROUND: State-based peer review organizations (PROs) and individual hospitals are challenged to achieve their quality improvement (QI) goals with shrinking resources. In 1993-1994 the Connecticut PRO and 15 local hospitals generated a comparative QI database on acute myocardial infarction (AMI) care for 1,202 Medicare and non-Medicare patients discharged in 1992 and 1993. METHODS: A steering committee composed of hospital and PRO representatives was assembled to provide oversight. PRO staff developed a chart abstraction tool and trained hospital abstractors who collected and submitted data to the PRO for comparative analyses. Written feedback was provided to all hospitals and supplemented with onsite presentations when requested. Each hospital prepared a written QI plan based on its unique data profile. RESULTS: Opportunities for improvement were identified at all hospitals. The most commonly targeted areas for improvement included the use of thrombolytics at presentation, aspirin at presentation and at discharge, and beta blockers at discharge. Improvement interventions included staff education sessions, development of AMI critical paths and standing orders, and storage of appropriate medications in emergency departments. Self-report data from the hospitals indicate improvements in care. DISCUSSION: PROs and hospitals can augment their individual QI activities by working together to share data, resources, and lessons learned. Twenty-three hospitals are now collaborating with the Connecticut PRO on a similarly designed QI project aimed at improving the care of patients hospitalized with atrial fibrillation. This project includes a more formal means of communicating QI interventions.

Optimal timing and indications for cholecystectomy in cardiac transplant patients.

Cardiac transplant is performed with increasing frequency as the treatment for end-stage cardiac disease. Although cholelithiasis is more frequent in both pretransplant and posttransplant patients, no standard management approach exists. Because many such patients are cared for outside the transplant center, it is important that general surgeons develop an appropriate strategy to manage this entity. We present our experience with 11 patients from our institution who underwent cholecystectomy before or after cardiac transplantation. In addition, we have reviewed the 76 reported cases of cholecystectomy performed in precardiac or postcardiac transplant patients from centers throughout the world. Any procedure in this patient group requires critical consideration in regard to the timing and type of procedure. Pretransplant patients are well recognized cardiac risks, and posttransplant immunosuppressed patients are at considerable risk for septic complications. Six patients underwent cholecystectomy prior to heart transplant. Five were performed laparoscopically, one as an open procedure. We also report five laparoscopic cholecystectomies in patients after cardiac transplant. One patient in the pretransplant group died 7 days after surgery from an uncontrollable arrhythmia. There were no hemodynamic or septic complications in either group. Current summated experience (87 cases) indicates that the mortality rate for urgent cholecystectomy in the posttransplant group is at least 36%. Because the first presentation of gallstones in this population is often acute cholecystitis, asymptomatic calculi cannot be considered benign. Elective cholecystectomy, laparoscopic or open, is tolerated well both before and after transplant. Given these facts, it seems reasonable to recommend pretransplant screening and posttransplant surveillance for gallstones.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of insulin on rat heart and skeletal muscle phenylalanyl-tRNA labeling and protein synthesis in vivo.

In vivo measurement of muscle protein synthesis and its hormonal regulation is limited by the difficulty of measuring aminoacyl-tRNA specific activity (SA). We assessed the kinetics of heart and skeletal muscle phenylalanyl-tRNA labeling during continuous infusion of L-[ring-2,6-3H]phenylalanine (Phe) to fasted anesthetized rats. We measured Phe SA in arterial and femoral venous plasma, the tissue acid-soluble pool and muscle protein hydrolysates after 5 min (n = 7), 30 min (n = 6), and 90 min (n = 7). We also assessed insulin's effect on labeling of the tRNA pool and muscle protein synthesis during a hyperinsulinemic clamp (2 mU.kg-1.min-1; n = 7). Labeling of tRNA in heart reached 59 +/- 5, 67 +/- 3, and 83 +/- 3% of arterial SA at 5, 30, and 90 min of saline infusion, respectively, but only 10 +/- 5, 34 +/- 2, and 48 +/- 2% in skeletal muscle at those times (P < 0.01 vs. heart). The tRNA SA was intermediate between SA in the acid-soluble pool and arterial plasma. Femoral venous SA was 32 +/- 2% lower (P < 0.001) than arterial SA. Skeletal muscle tRNA SA was also 29 +/- 3% lower (P < 0.001) than femoral venous SA. Insulin did not alter tRNA labeling and neither heart (9.8 +/- 1.1%/day for saline vs. 8.4 +/- 1.0%/day for insulin) nor skeletal muscle (6.7 +/- 1.5%/day vs. 4.2 +/- 0.4%/day) protein synthesis. Thus labeling of phenylalanyl-tRNA occurs more rapidly in heart than in skeletal muscle and is unaffected by insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Triple-label beta liquid scintillation counting.

The detection of radioactive compounds by liquid scintillation has revolutionized modern biology, yet few investigators make full use of the power of this technique. Even though multiple isotope counting is considerably more difficult than single isotope counting, many experimental designs would benefit from using more than one isotope. The development of accurate isotope counting techniques enabling the simultaneous use of three beta-emitting tracers has facilitated studies in our laboratory using the multiple tracer indicator dilution technique for assessing rates of transmembrane transport and cellular metabolism. The details of sample preparation, and of stabilizing the liquid scintillation spectra of the tracers, are critical to obtaining good accuracy. Reproducibility is enhanced by obtaining detailed efficiency/quench curves for each particular set of tracers and solvent media. The numerical methods for multiple-isotope quantitation depend on avoiding error propagation (inherent to successive subtraction techniques) by using matrix inversion. Experimental data obtained from triple-label beta counting illustrate reproducibility and good accuracy even when the relative amounts of different tracers in samples of protein/electrolyte solutions, plasma, and blood are changed.

Limited cytomegalovirus-specific immunoglobulin M and immunoglobulin G profiles in heart transplant recipients.

Twenty heart transplant recipients were assayed serially with cytomegalovirus cultures and with Western blot techniques for development of anticytomegalovirus immunoglobulin M (IgM) and immunoglobulin G (IgG). Patients were followed up 3 to 29 months (mean, 15 months) after transplantation. All but three patients received a 5-week perioperative course of passive immunization with immune globulin. Of nine seronegative patients with seropositive grafts, positive cytomegalovirous cultures developed in all, secondary organ involvement (gastrointestinal or pneumonia) developed in four of nine. Four of nine patients produced limited IgM profiles, consisting of only one to three bands; six of the nine patients had atypical, restricted IgG profiles. Three of four patients in whom secondary organ invasion developed had limited IgM profiles, and all four had atypical IgG profiles. Four of five patients with primary infection without symptoms produced full IgM profiles. Delay of IgM production until a time coincident with or after evidence of viral shedding was documented in all patients with primary infection and secondary organ involvement. Among 11 seropositive patients, five received seropositive grafts and six seronegative grafts. Of the five patients with seropositive grafts, positive cultures (reinfection) developed in three; all three responded with full IgM profiles. However, secondary organ involvement developed in two of these three in spite of full IgM profiles. Symptomatic illness did not develop in any patient with a seronegative donor, even in the presence of positive cultures (reactivation). Persistence of IgM for up to 26 months was found in all patients with primary infection or reinfection. In heart transplant recipients, limited IgM and IgG profiles in primary infection may confer increased risk of secondary organ invasion whereas the early development of full IgM profiles may correlate with disease without symptoms. In seropositive patients, production of full IgM profiles may not protect from reinfection with secondary organ involvement if the organ donor is seropositive, a potential source of a new viral strain.

In vivo measurement of myocardial protein turnover using an indicator dilution technique.

We applied a nondestructive tracer technique, previously developed for measuring skeletal muscle protein turnover, to the measurement of myocardial protein turnover in vivo. During a continuous infusion of L-[ring-2,6-3H]phenylalanine to anesthetized, overnight-fasted dogs, we measured the uptake of radiolabeled phenylalanine from plasma and the release of unlabeled phenylalanine from myocardial proteolysis using arterial and coronary sinus catheterization and analytic methods previously applied to skeletal muscle. Using these measurements, together with a model of myocardial protein synthesis that assumes rapid equilibration of tracer specific activity between myocardial phenylalanyl-tRNA and circulating phenylalanine, we estimated the rates of heart protein synthesis and degradation. The rate of heart protein synthesis was also estimated directly from the incorporation of labeled phenylalanine into tissue protein. The use of [3H]phenylalanine was compared with L-[1-14C]leucine in the measurement of heart protein turnover in dogs given simultaneous infusion of both tracers. Leucine uptake and release by the myocardium exceeded that of phenylalanine by 3.1 +/- 0.4- and 1.7 +/- 0.3-fold, respectively, consistent with leucine's 2.4-fold greater abundance in heart protein and its metabolism via other pathways. Phenylalanine is the preferred tracer for use with this method because of its limited metabolic fate in muscle. One theoretical limitation to the method, slow equilibration of circulating labeled phenylalanine with myocardial phenylalanyl-tRNA, was resolved by comparison of these specific activities after a 30-minute infusion of labeled phenylalanine in the rat. A second, empirical limitation involves precision in the measurement of the small decrements in phenylalanine specific activity that occur with each pass of blood through the coronary circulation. This was addressed by improving the precision of both the measurements of phenylalanine concentration and phenylalanine specific activity using high-performance liquid chromatography. We conclude that the in vivo measurement of phenylalanine tracer exchange across the myocardium permits the nondestructive estimation of heart protein turnover in the intact animal.

Metabolic and functional effects of perfluorocarbon distal perfusion during coronary angioplasty.

Myocardial lactate metabolism and left ventricular function were studied in 12 patients during angioplasty of the left anterior descending artery performed with distal coronary perfusion (oxygenated and nonoxygenated Fluosol) and by conventional technique without distal perfusion. Before balloon inflation there was net lactate extraction by the heart (31 +/- 6%). During balloon inflations performed with distal perfusion there was net lactate release into the great cardiac vein while the balloon was inflated; the great cardiac vein lactate concentration was approximately 25% lower during perfusion with oxygenated versus nonoxygenated Fluosol (p less than 0.02) indicating less myocardial lactate release. After balloon deflation washout of lactate into the great cardiac vein (net myocardial release) was observed in all 3 protocols. Left ventricular ejection fraction measured by echocardiography decreased markedly during nonperfused (53 +/- 3 to 36 +/- 3%, p less than 0.001) and nonoxygenated Fluosol (52 +/- 2 to 30 +/- 3%, p less than 0.001) inflations. This dysfunction was largely prevented by oxygenated Fluosol where only a minimal decrease in ejection fraction (51 +/- 2 vs 48 +/- 2%, p less than 0.02) occurred. Analysis of regional contractile function yielded similar results. Although oxygenated perfluorocarbons decrease cardiac lactate release during angioplasty, this study provides evidence for the onset of lactate production even when ventricular function is preserved.

An isotopic method for measurement of muscle protein synthesis and degradation in vivo.

In eight anaesthetized post-absorptive dogs we measured the concentration and specific radioactivity of phenylalanine and leucine in arterial and femoral-venous plasma, together with hindlimb flow during a continuous infusion of L-[ring-2,6-3H]phenylalanine and [1-14C]leucine. The femoral-venous plasma concentration was greater than arterial for both phenylalanine and leucine (P less than 0.05 for each). Despite net amino acid release there was a significant removal of both labelled phenylalanine and labelled leucine. Consequently, a significant dilution of specific radioactivity was observed between artery and vein for both radio-tracers. The uptake of leucine from the arterial circulation by the hindlimb exceeded by 2.6-fold that of phenylalanine; the measured molar ratio of leucine to phenylalanine in hindlimb muscle protein averaged 2.4 +/- 0.1. Since phenylalanine is neither synthesized nor degraded by muscle tissue, the measured removal of tracer and the dilution of tracer specific radioactivity across the hindlimb can be used to estimate rates of phenylalanine incorporation into, and release from, tissue protein. The estimated rate of protein synthesis by hindlimb averaged 644 +/- 250 nmol of phenylalanine/min. This was exceeded by the rate of tissue protein degradation (987 +/- 285 nmol of phenylalanine/min). The present results demonstrate that the dilution of the specific radioactivity of labelled phenylalanine can be readily measured across dog hindlimb. This measurement, coupled with an estimate of tissue blood flow, can provide a readily measured, non-destructive, method for estimation of protein turnover in specific muscle beds in vivo. Measurements can be made repeatedly over time in a single experiment, allowing the study of factors which regulate protein turnover. The method developed here in dogs can be readily extended to clinical studies.