Acute hospital care is the chief driver of regional spending variation in Medicare patients with advanced cancer

The root causes of regional variation in medical spending are poorly understood and vary by clinical condition. To identify drivers of regional spending variation for Medicare patients with advanced cancer, we used linked Surveillance, Epidemiology, and End Results program (SEER)-Medicare data from the period 2004-10. We broke down Medicare spending into thirteen cancer-relevant service categories. We then calculated the contribution of each category to spending and regional spending variation. Acute hospital care was the largest component of spending and the chief driver of regional spending variation, accounting for 48 percent of spending and 67 percent of variation. In contrast, chemotherapy accounted for 16 percent of spending and 10 percent of variation. Hospice care constituted 5 percent of spending. However, variation in hospice spending was fully offset by opposing variation in other categories. Our analysis suggests that the strategy with the greatest potential to improve the value of care for patients with advanced cancer is to reduce reliance on acute hospital care for this patient population.

Characteristics Associated with In-Hospital Death among Commercially Insured Decedents with Cancer

BACKGROUND

A majority of patients with poor-prognosis cancer express a preference for in-home death; however, in-hospital deaths are common.

OBJECTIVE

We sought to identify characteristics associated with in-hospital death.

DESIGN

Case series.

SETTING/SUBJECTS

Commercially insured patients with cancer who died between July 2010 and December 2013 and who had at least two outpatient visits at a tertiary cancer center during the last six months of life.

MEASUREMENTS

Patient characteristics, healthcare utilization, and in-hospital death (primary outcome) were ascertained from institutional records and healthcare claims. Bivariate and multivariable analyses were used to evaluate the association of in-hospital death with patient characteristics and end-of-life outcome measures.

RESULTS

We identified 904 decedents, with a median age of 59 years at death. In-hospital death was observed in 254 patients (28%), including 110 (12%) who died in an intensive care unit. Hematologic malignancy was associated with a 2.57 times increased risk of in-hospital death (95% confidence interval [CI] 1.91-3.45, p < 0.001), and nonenrollment in hospice was associated with a 14.5 times increased risk of in-hospital death (95% CI 9.81-21.4, p < 0.001). Time from cancer diagnosis to death was also associated with in-hospital death (p = 0.003), with the greatest risk among patients dying within six months of cancer diagnosis. All significant associations persisted in multivariable analyses that were adjusted for baseline characteristics.

CONCLUSIONS

In-hospital deaths are common among commercially insured cancer patients. Patients with hematologic malignancy and patients who die without receiving hospice services have a substantially higher incidence of in-hospital death.

Early Pancreatic Ductal Adenocarcinoma Survival Is Dependent on Size: Positive Implications for Future Targeted Screening

OBJECTIVES

Pancreatic ductal adenocarcinoma (PDAC) has not experienced a meaningful mortality improvement for the past few decades. Successful screening is difficult to accomplish because most PDACs present late in their natural history, and current interventions have not provided significant benefit. Our goal was to identify determinants of survival for early PDAC to help inform future screening strategies.

METHODS

Early PDACs from the National Cancer Institute's Surveillance, Epidemiology, and End Results Program database (2000-2010) were analyzed. We stratified by size and included carcinomas in situ (Tis). Overall cancer-specific survival was calculated. A Cox proportional hazards model was developed and the significance of key covariates for survival prediction was evaluated.

RESULTS

A Kaplan-Meier plot demonstrated significant differences in survival by size at diagnosis; these survival benefits persisted after adjustment for key covariates in the Cox proportional hazards analysis. In addition, relatively weaker predictors of worse survival included older age, male sex, black race, nodal involvement, tumor location within the head of the pancreas, and no surgery or radiotherapy.

CONCLUSIONS

For early PDAC, we found tumor size to be the strongest predictor of survival, even after adjustment for other patient characteristics. Our findings suggest that early PDAC detection can have clinical benefit, which has positive implications for future screening strategies.

An ED pilot intervention to facilitate outpatient acute care for cancer patients

INTRODUCTION

Unplanned hospitalizations are common in patients with cancer, and most hospitalizations originate in the emergency department (ED).

METHODS

We implemented an ED-based pilot intervention designed to reduce hospitalizations among patients with solid tumors. The intervention, piloted at a single academic medical center, involved a medical oncologist embedded in the ED during evening hours. We used a quasiexperimental preimplementation/postimplementation study design to evaluate the proportion of ED visits that resulted in inpatient hospital admission, before and after pilot implementation. General estimating equations were used to evaluate the association between the intervention and hospital admission.

RESULTS

There were 390 ED visits by eligible cancer patients in the preintervention period and 418 visits in the intervention period. During the intervention period, 158 (38%) of 418 ED visits were identified by the embedded oncologist during the evening intervention shift. The proportion of ED visits leading to hospitalization was 70% vs 69% in the preintervention and intervention periods (odds ratio, 0.93 [95% confidence interval, 0.69-1.24]; P= .62). There were no differences between periods in ED length of stay or subsequent use of acute care. Among patients with initial ED presentation during the operating hours of the intervention, the proportion of ED visits leading to hospitalization was 77% vs 67% in the preintervention and intervention periods (odds ratio, 0.62 [0.36-1.08]; P= .08).

CONCLUSION

Embedding an oncologist in the ED of an academic medical center did not significantly reduce hospital admissions. Novel approaches are needed to strengthen outpatient acute care for patients with cancer.

A Clinical Prediction Model to Assess Risk for Chemotherapy-Related Hospitalization in Patients Initiating Palliative Chemotherapy

IMPORTANCE

Chemotherapy-related hospitalizations in patients with advanced cancer are common, distressing, and costly. Methods to identify patients at high risk of chemotherapy toxic effects will permit development of targeted strategies to prevent chemotherapy-related hospitalizations.

OBJECTIVE

To demonstrate the feasibility of using readily available clinical data to assess patient-specific risk of chemotherapy-related hospitalization.

DESIGN, SETTING, AND PARTICIPANTS

Nested case-control study conducted from January 2003 through December 2011 at the Mass General/North Shore Cancer Center, a community-based cancer center in northeastern Massachusetts. The parent cohort included 1579 consecutive patients with advanced solid-tumor cancer receiving palliative-intent chemotherapy. Case patients (n = 146) included all patients from the parent cohort who experienced a chemotherapy-related hospitalization. Controls (n = 292) were randomly selected from 1433 patients who did not experience a chemotherapy-related hospitalization.

EXPOSURES

Putative risk factors for chemotherapy-related hospitalization-including patient characteristics, treatment characteristics, and pretreatment laboratory values-were abstracted from medical records. Multivariable logistic regression was used to model the patient-specific risk of chemotherapy-related hospitalization.

MAIN OUTCOMES AND MEASURES

Chemotherapy-related hospitalization, as adjudicated by the oncology clinical care team within a systematic quality-assessment program.

RESULTS

A total of 146 (9.2%) of 1579 patients from the parent cohort experienced a chemotherapy-related hospitalization. In multivariate regression, 7 variables were significantly associated with chemotherapy-related hospitalization: age, Charlson comorbidity score, creatinine clearance, calcium level, below-normal white blood cell and/or platelet count, polychemotherapy (vs monotherapy), and receipt of camptothecin chemotherapy. The median predicted risk of chemotherapy-related hospitalization was 6.0% (interquartile range [IQR], 3.6%-11.4%) in control patients and 14.7% (IQR, 6.8%-22.5%) in case patients. The bootstrap-adjusted C statistic was 0.71 (95% CI, 0.66-0.75). At a risk threshold of 15%, the model exhibited a sensitivity of 49% (95% CI, 41%-57%) and a specificity of 85% (95% CI, 81%-89%) for predicting chemotherapy-related hospitalization.

CONCLUSIONS AND RELEVANCE

In patients initiating palliative chemotherapy for cancer, readily available clinical data were associated with the patient-specific risk of chemotherapy-related hospitalization. External validation and evaluation in the context of a clinical decision support tool are warranted.

Forty-Year Trends in Cholangiocarcinoma Incidence in the U.S.: Intrahepatic Disease on the Rise

The recognized incidence of intrahepatic cholangiocarcinoma in the U.S. continues to rise, whereas the incidence of extrahepatic cholangiocarcinoma is stable. The incidence of carcinoma of unknown primary has fallen dramatically during the same time period.

Background.

Challenges in the diagnosis and classification of cholangiocarcinoma have made it difficult to quantify the true incidence of this highly aggressive malignancy.

Methods.

We analyzed the Surveillance, Epidemiology, and End Results data to assess long-term trends in the age-standardized incidence of intrahepatic and extrahepatic cholangiocarcinoma between 1973 and 2012, correcting for systematic coding errors. Because intrahepatic cholangiocarcinoma (ICC) may frequently be misdiagnosed as cancer of unknown primary (CUP), we also analyzed trends in the incidence of CUP.

Results.

Between 1973 and 2012, the reported U.S. incidence of ICC increased from 0.44 to 1.18 cases per 100,000, representing an annual percentage change (APC) of 2.30%; this trend has accelerated during the past decade to an APC of 4.36%. The incidence of extrahepatic cholangiocarcinoma increased modestly from 0.95 to 1.02 per 100,000 during the 40-year period (APC, 0.14%). The incidence of CUP with histologic features potentially consistent with cholangiocarcinoma decreased by 51% between 1973 and 2012 (APC, −1.87%), whereas the incidence of CUP with squamous or nonepithelial histologic features increased modestly (APC, 0.42%).

Conclusion.

The recognized incidence of ICC in the U.S. continues to rise, whereas the incidence of ECC is stable. The incidence of CUP has fallen dramatically during the same time period.

Implications for Practice:

Clinical distinctions between cholangiocarcinoma (particularly intrahepatic cholangiocarcinoma [ICC]) and cancer of unknown primary (CUP) can be challenging. Recent discoveries have identified recurrent and potentially targetable genomic abnormalities in ICC, highlighting the importance of improving diagnosis. This study demonstrates that the incidence of ICC is increasing in the U.S., whereas the incidence of extrahepatic cholangiocarcinoma is stable. Concomitantly, the incidence of CUP has declined dramatically, suggesting that improved distinction between ICC and CUP may be a major driver of the increasing recognized incidence of ICC. The increasing incidence of ICC warrants further study of prevention and treatment approaches.

Intensity of Medical Interventions between Diagnosis and Death in Patients with Advanced Lung and Colorectal Cancer: A CanCORS Analysis

BACKGROUND

Medical interventions are an important component of the illness experience in advanced cancer.

OBJECTIVE

To describe the use of medical interventions between diagnosis and death in decedents with metastatic lung and colorectal cancer.

DESIGN

Retrospective analysis of a prospective cohort study.

SETTING/SUBJECTS

We studied 1,840 decedents from the Cancer Care Outcomes Research and Surveillance (CanCORS) study. Subjects had been diagnosed with stage IV lung or colorectal cancer between 2003 and 2005.

MEASUREMENTS

Hospitalizations, surgeries, radiation therapy treatments, chemotherapy treatments, and end-of-life care, reported by tertile of overall survival time.

RESULTS

Median survival in the bottom, middle, and top tertiles of survival was 1.2, 5.3, and 15.3 months for lung cancer, and 3.0, 18.0, and 44.4 months for colorectal cancer. Hospitalizations, chemotherapy receipt, and hospice enrollment increased with increasing survival. The median duration of chemotherapy in the top survival tertile was 149 days for lung cancer and 498 days for colorectal cancer. A minority of decedents used any hospice services, and the median duration of hospice enrollment exceeded 30 days only for enrollees in the top survival tertile (lung cancer, 35 days; colorectal cancer, 66 days).

CONCLUSIONS

For patients with metastatic lung and colorectal cancer, longer survival is associated with increased intensity of medical care, characterized by greater use of chemotherapy and acute hospital care. Hospice utilization was uniformly low, and most hospice enrollees were referred to hospice in the last 30 days of life.

Identification of potentially avoidable hospitalizations in patients with GI cancer

PURPOSE

To identify and characterize potentially avoidable hospitalizations in patients with GI malignancies.

PATIENTS AND METHODS

We compiled a retrospective series of sequential hospital admissions in patients with GI cancer. Patients were admitted to an inpatient medical oncology or palliative care service between December 2011 and July 2012. Practicing oncology clinicians used a consensus-driven medical record review process to categorize each hospitalization as "potentially avoidable" or "not avoidable." Patient demographic and clinical data were abstracted, and quantitative and qualitative analyses were performed to identify patient characteristics and outcomes associated with potentially avoidable hospitalizations.

RESULTS

We evaluated 201 hospitalizations in 154 unique patients. The median age was 62 years, and colorectal cancer was the most common diagnosis (32%). The majority of hospitalized patients had metastatic cancer (81%). In all, 53% of hospitalizations were attributable to cancer symptoms, and 28% were attributable to complications of cancer treatment. Medical oncologists identified 39 hospitalizations (19%) as potentially avoidable. Hospitalizations were more likely to be categorized as potentially avoidable for patients with the following characteristics: age ≥ 70 years (odds ratio [OR], 2.63; 95% CI, 1.15 to 6.02), receipt of an oncologist's advice to consider hospice (OR, 6.09; 95% CI, 2.54 to 14.58), or receipt of three or more lines of chemotherapy (OR, 2.68; 95% CI, 1.01 to 7.08). Ninety-day mortality was higher after avoidable hospitalizations compared with hospitalizations that were not avoidable (OR, 6.4; 95% CI, 1.8 to 22.3).

CONCLUSION

Potentially avoidable hospitalizations are common in patients with advanced GI cancer. The majority of potentially avoidable hospitalizations occurred in patients with advanced treatment-refractory cancers near the end of life.

National trends in pancreatic cancer outcomes and pattern of care among Medicare beneficiaries, 2000 through 2010

BACKGROUND

Pancreatic cancer is a major cause of morbidity and mortality in the Medicare population. Whether the health care burden of pancreatic cancer has changed over the last decade is unknown.

METHODS

The authors used Medicare data from 2000 to 2010 to identify beneficiaries aged ≥ 65 years who were hospitalized for the management of pancreatic cancer. Annual trends were estimated for the age-sex-race-adjusted initial hospitalization rate, the age-sex-race-comorbidity-adjusted 1-year mortality rate after initial hospitalization, age-sex-race-comorbidity-adjusted procedure rates, 1-year all-cause rehospitalizations after initial pancreatic cancer hospitalization, and mean inflation-adjusted Medicare payment for initial hospitalization.

RESULTS

A total of 130,728 patients had ≥ 1 hospitalizations for pancreatic cancer and were identified from 56,642,071 beneficiaries during the study period. The age-sex-race-adjusted rate of initial hospitalization for pancreatic cancer was 50 per 100,000 person-years in 2010, representing a 0.5% annual increase since 2000 (95% confidence interval [95% CI], 0.3%-0.7%). In the same period, the age-sex-race-comorbidity-adjusted 1-year mortality rate decreased by 4.4% (95% CI, 3.9%-4.9%), and the age-sex-race-comorbidity-adjusted surgical resection rate increased by 6.9% (95% CI, 6.4%-7.5%). The mean inflation-adjusted Medicare payment for the initial hospitalization decreased, from $14,118 in 2000 to $13,318 in 2010, and the number of 1-year all-cause rehospitalizations after the initial hospitalization increased from 0.75 per patient in 2000 to 0.82 per patient in 2009 (all P < .001).

CONCLUSIONS

For Medicare fee-for-service beneficiaries, initial pancreatic cancer hospitalization, surgical resection, and rehospitalization rates increased, but 1-year mortality rates declined over the last decade.

Regional variation in spending and survival for older adults with advanced cancer

BACKGROUND

Medicare spending varies substantially across the United States. We evaluated the association between mean regional spending and survival in advanced cancer.

METHODS

We identified 116 523 subjects with advanced cancer from 2002 to 2007, using Surveillance, Epidemiology and End Results (SEER)-Medicare linked data. Subjects were aged 65 years and older with non-small cell lung, colon, breast, prostate, or pancreas cancer. Of these subjects, 61 083 had incident advanced-stage cancer (incident cohort) and 98 935 had death from cancer (decedent cohort); 37% of subjects were included in both cohorts. Subjects were linked to one of 80 hospital referral regions within SEER areas. We estimated mean regional spending in both cohorts. We assessed the primary outcome, survival, in the incident cohort; the exposure measure was the quintile of regional spending in the decedent cohort. Survival in quintiles 2 through 5 was compared with that in quintile 1 (lowest spending quintile) using Cox regression models.

RESULTS

From quintile 1 to 5, mean regional spending increased by 32% and 41% in the incident and decedent cohorts (incident cohort: $28 854 to $37 971; decedent cohort: $27 446 to $38 630). The association between spending and survival varied by cancer site and quintile; hazard ratios ranged from 0.92 (95% confidence interval [CI] = 0.82 to 1.04, pancreas cancer quintile 5) to 1.24 (95% CI = 1.11 to 1.39, breast cancer quintile 3). In most cases, differences in survival between quintile 1 and quintiles 2 through 5 were not statistically significant.

CONCLUSION

There is substantial regional variation in Medicare spending for advanced cancer, yet no consistent association between mean regional spending and survival.

Twelve weeks of endurance training increases FFA mobilization and reesterification in postmenopausal women

We examined the effects of exercise intensity and training on rates of lipolysis, plasma free fatty acid (FFA) appearance (R(a)), disappearance (R(d)), reesterification (R(s)), and oxidation (R(oxP)) in postmenopausal (PM) women. Ten sedentary but healthy women (55 ± 0.6 yr) completed 12 wk of supervised endurance exercise training on a cycle ergometer [5 days/wk, 1 h/day, 65% peak oxygen consumption (Vo(2peak))]. Flux rates were determined by continuous infusion of [1-(13)C]palmitate and [1,1,2,3,3-(2)H(5)]glycerol during 90 min of rest and 60 min of cycle ergometer exercise during one pretraining exercise trial [65% Vo(2peak) (PRE)] and two posttraining exercise trials [at power outputs that elicited 65% pretraining Vo(2peak) (absolute training; ABT) and 65% posttraining Vo(2peak) (relative training; RLT)]. Initial body weights (68.2 ± 4.5 kg) were maintained over the course of study. Training increased Vo(2peak) by 16.3 ± 3.9% (P < 0.05) (Zarins ZA, Wallis GA, Faghihnia N, Johnson ML, Fattor JA, Horning MA and Brooks GA. Metabolism 58: 9: 1338-1346, 2009). Glycerol R(a) and R(d) were elevated in the RLT trial (P < 0.05), but not the ABT trial after training. Rates of plasma FFA R(a), R(d), and R(oxP) were elevated during the ABT compared with PRE trial (P < 0.05). FFA R(s) accounted for most (50-70%) of R(d) during exercise; training reduced FFA R(s) during ABT, but not RLT compared with PRE. We conclude that, despite the large age-related decrease in metabolic scope in PM women, endurance training increases the capacities for FFA mobilization and oxidation during exercises of a given power output. However, after menopause, total lipid oxidation capacity remains low, with reesterification accounting for most of FFA R(d).

Childhood cancer in families with and without BRCA1 or BRCA2 mutations ascertained at a high-risk breast cancer clinic

BACKGROUND

Germline mutations in the BRCA1 and BRCA2 genes are associated with breast cancer, ovarian cancer and other malignancies. Biallelic mutations of BRCA2 are a cause of Fanconi anemia and characteristic childhood cancers. We undertook this study to evaluate the contribution of familial BRCA mutations to childhood cancer in hereditary breast cancer families.

PATIENTS AND METHODS

We compared the prevalence of childhood cancers in 379 families with BRCA1 or BRCA2 mutations and 426 families without mutations. All families were ascertained at a high-risk breast cancer clinic. Our study included first- through fourth-degree relatives of BRCA mutation carriers and cancer-affected individuals with negative testing for BRCA mutations. The primary endpoint was any case of childhood cancer (diagnosed < age 21).

RESULTS

20 cases of childhood cancer occurred in 379 families with BRCA1 or BRCA2 mutations and 35 cases of childhood cancer occurred in 426 families with negative mutation testing (p = 0.12). Nine childhood cancers occurred in 240 families with BRCA1 mutations, and 11 childhood cancers occurred in 141 families with BRCA2 mutations (p = 0.1). 13 of 18 families with childhood cancer and BRCA1 or BRCA2 mutations (72%) and 13 of 31 families with childhood cancer and negative mutation testing (42%) met the Birch criteria for Li-Fraumeni like syndrome (LFL).

CONCLUSIONS

In this retrospective analysis, heterozygous BRCA1 and BRCA2 mutations were not a risk factor for childhood cancer in hereditary breast cancer families. These data support the current practice of delaying BRCA mutation testing until adulthood.

Recovery of (13)CO2 during rest and exercise after [1-(13)C]acetate, [2-(13)C]acetate, and NaH(13)CO3 infusions

For estimating the oxidation rates (Rox) of glucose and other substrates by use of (13)C-labeled tracers, we obtained correction factors to account for label dilution in endogenous bicarbonate pools and TCA cycle exchange reactions. Fractional recoveries of (13)C label in respiratory gases were determined during 225 min of rest and 90 min of leg cycle ergometry at 45 and 65% peak oxygen uptake (VO(2 peak)) after continuous infusions of [1-(13)C]acetate, [2-(13)C]acetate, or NaH(13)CO(3). In parallel trials, [6,6-(2)H]glucose and [1-(13)C]glucose were given. Experiments were conducted after an overnight fast with exercise commencing 12 h after the last meal. During the transition from rest to exercise, CO(2) production increased (P < 0.05) in an intensity-dependent manner. Significant differences were observed in the fractional recoveries of (13)C label as (13)CO(2) at rest (NaH(13)CO(3), 77.5 +/- 2.8%; [1-(13)C]acetate, 49.8 +/- 2.4%; [2-(13)C]acetate, 26.1 +/- 1.4%). During exercise, fractional recoveries of (13)C label from [1-(13)C]acetate, [2-(13)C]acetate, and NaH(13)CO(3) were increased compared with rest. Magnitudes of label recoveries during both exercise intensities were tracer specific (NaH(13)CO(3), 93%; [1-(13)C]acetate, 80%; [2-(13)C]acetate, 65%). Use of an acetate-derived correction factor for estimating glucose oxidation resulted in Rox values in excess (P < 0.05) of glucose rate of disappearance during hard exercise. We conclude that, after an overnight fast: 1) recovery of (13)C label as (13)CO(2) from [(13)C]acetate is decreased compared with bicarbonate; 2) the position of (13)C acetate label affects carbon dilution estimations; 3) recovery of (13)C label increases in the transition from rest to exercise in an isotope-dependent manner; and 4) application of an acetate correction factor in glucose oxidation measurements results in oxidation rates in excess of glucose disappearance during exercise at 65% of VO(2 peak). Therefore, bicarbonate, not acetate, correction factors are advocated for estimating glucose oxidation from carbon tracers in exercising men.

Autoregulation of glucose production in men with a glycerol load during rest and exercise

Related to hepatic autoregulation we evaluated hypotheses that 1) glucose production would be altered as a result of a glycerol load, 2) decreased glucose recycling rate (Rr) would result from increased glycerol uptake, and 3) the absolute rate of gluconeogenesis (GNG) from glycerol would be positively correlated to glycerol rate of disappearance (R(d)) during a glycerol load. For these purposes, glucose and glycerol kinetics were determined in eight men during rest and during 90 min of leg cycle ergometry at 45 and 65% of peak O2 consumption (.VO2 (peak)). Trials were conducted after an overnight fast, with exercise commencing 12 h after the last meal. Subjects received a continuous infusion of [6,6-(2)H(2)]glucose, [1-(13)C]glucose, and [1,1,2,3,3-(2)H(5)]glycerol without (CON) or with an additional 1,000 mg (rest: 20 mg/min; exercise: 40 mg/min) of [2-(13)C]- or unlabeled glycerol added to the infusate (GLY). Infusion of glycerol dampened glucose Rr, calculated as the difference between [6,6-(2)H(2)]- and [1-(13)C]glucose rates of appearance (R(a)), at rest [0.35 +/- 0.12 (CON) vs. 0.12 +/- 0.10 mg. kg(-1). min(-1) (GLY), P < 0.05] and during exercise at both intensities [45%: 0.63 +/- 0.14 (CON) vs. 0.04 +/- 0.12 (GLY); 65%: 0.73 +/- 0.14 (CON) vs. 0.04 +/- 0.17 mg. kg(-1). min(-1) (GLY), P < 0.05]. Glucose R(a) and oxidation were not affected by glycerol infusion at rest or during exercise. Throughout rest and both exercise intensities, glycerol R(d) was greater in GLY vs. CON conditions (rest: 0.30 +/- 0.04 vs. 0.58 +/- 0.04; 45%: 0.57 +/- 0.07 vs. 1.19 +/- 0.04; 65%: 0.73 +/- 0.06 vs. 1.27 +/- 0.05 mg. kg(-1). min(-1), CON vs. GLY, respectively). Differences in glycerol R(d) (DeltaR(d)) between protocols equaled the unlabeled glycerol infusion rate and correlated with plasma glycerol concentration (r = 0.97). We conclude that infusion of a glycerol load during rest and exercise at 45 and 65% of .VO2(peak) 1) does not affect glucose R(a) or R(d), 2) blocks glucose Rr, 3) increases whole body glycerol R(d) in a dose-dependent manner, and 4) results in gluconeogenic rates from glycerol equivalent to CON glucose recycling rates.

The effects of endurance training and exhaustive exercise on mitochondrial enzymes in tissues of the rat (Rattus norvegicus)

The aim of the present study was to ascertain the effects of training and exhaustive exercise on mitochondrial capacities to oxidize pyruvate, 2-oxoglutarate, palmitoylcarnitine, succinate and ferrocytochrome c in various tissues of the rat. Endurance capacity was significantly increased (P<0.01) by an endurance training program over a period of 5-6 weeks. The average run time to exhaustion was 214.2+/-23.8 min for trained rats in comparison with 54.5+/-11.7 min for their untrained counterparts. Oxidative capacities were reduced in liver (P<0.05) and brown adipose tissue (P<0.05) as a result of endurance training. On the contrary, the oxidative capacity of skeletal muscle was slightly increased and that of heart almost unaffected except for the oxidation of palmitoylcarnitine, which was significantly reduced (P<0.05) as a result of training.

Chronically and acutely exercised rats: biomarkers of oxidative stress and endogenous antioxidants

The responses to oxidative stress induced by chronic exercise (8-wk treadmill running) or acute exercise (treadmill running to exhaustion) were investigated in the brain, liver, heart, kidney, and muscles of rats. Various biomarkers of oxidative stress were measured, namely, lipid peroxidation [malondialdehyde (MDA)], protein oxidation (protein carbonyl levels and glutamine synthetase activity), oxidative DNA damage (8-hydroxy-2'-deoxyguanosine), and endogenous antioxidants (ascorbic acid, alpha-tocopherol, glutathione, ubiquinone, ubiquinol, and cysteine). The predominant changes are in MDA, ascorbic acid, glutathione, cysteine, and cystine. The mitochondrial fraction of brain and liver showed oxidative changes as assayed by MDA similar to those of the tissue homogenate. Our results show that the responses of the brain to oxidative stress by acute or chronic exercise are quite different from those in the liver, heart, fast muscle, and slow muscle; oxidative stress by acute or chronic exercise elicits different responses depending on the organ tissue type and its endogenous antioxidant levels.

Intra- and extra-cellular lactate shuttles

The "lactate shuttle hypothesis" holds that lactate plays a key role in the distribution of carbohydrate potential energy that occurs among various tissue and cellular compartments such as between: cytosol and mitochondria, muscle and blood, blood and muscle, active and inactive muscles, white and red muscles, blood and heart, arterial blood and liver, liver and other tissues such as exercising muscle, intestine and portal blood, portal blood and liver, zones of the liver, and skin and blood. Studies on resting and exercising humans indicate that most lactate (75-80%) is disposed of through oxidation, with much of the remainder converted to glucose and glycogen. Lactate transport across cellular membranes occurs by means of facilitated exchange along pH and concentration gradients involving a family of lactate transport proteins, now called monocarboxylate transporters (MCTs). Current evidence is that muscle and other cell membrane lactate transporters are abundant with characteristics of high Km and Vmax. There appears to be long-term plasticity in the number of cell membrane transporters, but short-term regulation by allosteric modulation or phosphorylation is not known. In addition to cell membranes, mitochondria also contain monocarboxylate transporters (mMCT) and lactic dehydrogenase (mLDH). Therefore, mitochondrial monocarboxylate uptake and oxidation, rather than translocation of transporters to the cell surfaces, probably regulate lactate flux in vivo. Accordingly, the "lactate shuttle" hypothesis has been modified to include a new, intracellular component involving cytosolic to mitochondrial exchange. The intracellular lactate shuttle emphasizes the role of mitochondrial redox in the oxidation and disposal of lactate during exercise and other conditions.

Endurance training, expression, and physiology of LDH, MCT1, and MCT4 in human skeletal muscle

To evaluate the effects of endurance training on the expression of monocarboxylate transporters (MCT) in human vastus lateralis muscle, we compared the amounts of MCT1 and MCT4 in total muscle preparations (MU) and sarcolemma-enriched (SL) and mitochondria-enriched (MI) fractions before and after training. To determine if changes in muscle lactate release and oxidation were associated with training-induced changes in MCT expression, we correlated band densities in Western blots to lactate kinetics determined in vivo. Nine weeks of leg cycle endurance training [75% peak oxygen consumption (VO(2 peak))] increased muscle citrate synthase activity (+75%, P < 0.05) and percentage of type I myosin heavy chain (+50%, P < 0.05); percentage of MU lactate dehydrogenase-5 (M4) isozyme decreased (-12%, P < 0.05). MCT1 was detected in SL and MI fractions, and MCT4 was localized to the SL. Muscle MCT1 contents were consistent among subjects both before and after training; in contrast, MCT4 contents showed large interindividual variations. MCT1 amounts significantly increased in MU, SL, and MI after training (+90%, +60%, and +78%, respectively), whereas SL but not MU MCT4 content increased after training (+47%, P < 0.05). Mitochondrial MCT1 content was negatively correlated to net leg lactate release at rest (r = -0.85, P < 0.02). Sarcolemmal MCT1 and MCT4 contents correlated positively to net leg lactate release at 5 min of exercise at 65% VO(2 peak) (r = 0.76, P < 0.03 and r = 0. 86, P < 0.01, respectively). Results support the conclusions that 1) endurance training increases expression of MCT1 in muscle because of insertion of MCT1 into both sarcolemmal and mitochondrial membranes, 2) training has variable effects on sarcolemmal MCT4, and 3) both MCT1 and MCT4 participate in the cell-cell lactate shuttle, whereas MCT1 facilitates operation of the intracellular lactate shuttle.

Endurance training increases gluconeogenesis during rest and exercise in men

The hypothesis that endurance training increases gluconeogenesis (GNG) during rest and exercise was evaluated. We determined glucose turnover with [6,6-(2)H]glucose and lactate incorporation into glucose by use of [3-(13)C]lactate during 1 h of cycle ergometry at two intensities [45 and 65% peak O(2) consumption (VO(2 peak))] before and after training [65% pretraining VO(2 peak)], same absolute workload (ABT), and 65% posttraining VO(2 peak), same relative intensity (RLT). Nine males (178.1 +/- 2.5 cm, 81.8 +/- 3.3 kg, 27.4 +/- 2.0 yr) trained for 9 wk on a cycle ergometer 5 times/wk for 1 h at 75% VO(2 peak). The power output that elicited 66.0 +/- 1.1% of VO(2 peak) pretraining elicited 54.0 +/- 1.7% posttraining. Rest and exercise arterial glucose concentrations were similar before and after training, regardless of exercise intensity. Arterial lactate concentration during exercise was significantly greater than at rest before and after training. Compared with 65% pretraining, arterial lactate concentration decreased at ABT (4.75 +/- 0.4 mM, 65% pretraining; 2.78 +/- 0.3 mM, ABT) and RLT (3.76 +/- 0.46 mM) (P < 0.05). At rest after training, the percentage of glucose rate of appearance (R(a)) from GNG more than doubled (1.98 +/- 0.5% pretraining; 5.45 +/- 1.3% posttraining), as did the rate of GNG (0.11 +/- 0.03 mg x kg(-1) x min(-1) pretraining, 0.24 +/- 0.06 mg x kg(-1) x min(-1) posttraining). During exercise after training, %glucose R(a) from GNG increased significantly at ABT (2.3 +/- 0.8% at 65% pre- vs. 7.6 +/- 2.1% posttraining) and RLT (6.1 +/- 1.5%), whereas GNG increased almost threefold (P < 0.05) at ABT (0.24 +/- 0.08 mg x kg(-1) x min(-1) 65% pre-, and 0.71 +/- 0.18 mg x kg(-1) x min(-1) posttraining) and RLT (0.75 +/- 0.26 mg x kg(-1) x min(-1)). We conclude that endurance training increases gluconeogenesis twofold at rest and threefold during exercise at given absolute and relative exercise intensities.

Are arterial, muscle and working limb lactate exchange data obtained on men at altitude consistent with the hypothesis of an intracellular lactate shuttle?

The "Lactate Shuttle" Hypothesis posits that lactate removal requires exchange among producing and consuming cells. The "Intra-cellular Lactate Shuttle" hypothesis posits that lactate exchange occurs among compartments within cells, and that mitochondria are the major sites of cellular lactate disposal. Thus, cells with high mitochondrial densities (cardiocytes, myocytes, hepatocytes) are those which participate in lactate clearance. The model of an Intracellular Lactate Shuttle recognizes that the Keq for LDH is 3.6 x 10(4) M-1; thus, glycolysis results in cytosolic lactate production regardless of the intracellular PO2. The model also requires presence of a mitochondrial monocarboxylate transporter (MCT) that allows uptake of lactate as well as pyruvate, and intra-mitochondrial LDH whose function is linked to the ETC, and which permits lactate-->pyruvate conversion and oxidation. Recently, we have shown that liver, heart and muscle mitochondria readily oxidize lactate and contain LDH and MCT1. Accordingly, we have concluded that lactate is the predominant monocarboxylate oxidized by mitochondria in vivo. The model of an "Intra-cellular Lactate Shuttle" is consistent with many of the observations on men at sea level and altitude. The observations include: oxidation is the primary fate of lactate disposal during rest and exercise; lactate production and oxidation occur simultaneously within resting and working muscle; increasing [lactate]a increases muscle lactate extraction, and that by increasing SaO2 acclimatization reduces blood [lactate].