Aging delays the suppression of lipolysis and fatty acid oxidation in the postprandial period.

Plasma glycerol and free fatty acid concentrations decrease following oral glucose consumption, but changes in the rate of lipolysis during an oral glucose tolerance test (OGTT) have not been documented in conjunction with changes in fatty acid (FA) oxidation or reesterification rates in healthy individuals. After a 12-h overnight fast, 15 young (21-35 yr; 7 men and 8 women) and 14 older (60-80 yr; 7 men and 7 women) participants had the forearm vein catheterized for primed continuous infusion of [1,1,2,3,3-H]glycerol. A contralateral hand vein was catheterized for arterialized blood sampling.

Delayed and diminished postprandial lactate shuttling in healthy older men and women.

Lactate, a product of glycolysis, is formed under aerobic conditions. Extensive work has shown lactate flux in young and exercising humans; however, the effect of age is not known. We tested the hypothesis that postprandial lactate shuttling (PLS) would be diminished in older adults.

Leg cycling efficiency is unaltered in healthy aging regardless of sex or training status.

Muscular efficiency during exercise has been used to interrogate aspects of human muscle energetics, including mitochondrial coupling and biomechanical efficiencies. Typically, assessments of muscular efficiency have involved graded exercises. Results of previous studies have been interpreted to indicate a decline in exercise efficiency with aging owing to decreased mitochondrial function.

Altered glucose kinetics occurs with aging: a new outlook on metabolic flexibility.

Our purpose was to determine how age affects metabolic flexibility and underlying glucose kinetics in healthy young and older adults. Therefore, glucose and lactate tracers along with pulmonary gas exchange data were used to determine glucose kinetics and respiratory exchange ratios [RER = carbon dioxide production (V̇co)/oxygen consumption (V̇o)] during a 2-h 75-g oral glucose tolerance test (OGTT). After an 12-h overnight fast, 28 participants, 15 young (21-35 yr; 7 men and 8 women) and 13 older (60-80 yr; 7 men and 6 women), received venous primed-continuous infusions of [6,6-H]glucose and [3-C]lactate with a [Formula: see text] bolus.

Enteric and systemic postprandial lactate shuttle phases and dietary carbohydrate carbon flow in humans.

Dietary glucose in excess is stored in the liver in the form of glycogen. As opposed to direct conversion of glucose into glycogen, the hypothesis of the postprandial lactate shuttle (PLS) proposes that dietary glucose uptake is metabolized to lactate in the gut, thereby being transferred to the liver for glycogen storage. In the present study, we provide evidence of a PLS in young healthy men and women.

Underfeeding Alters Brain Tissue Synthesis Rate in a Rat Brain Injury Model.

Brain injuries (BI) are highly disruptive, often having long lasting effects. Inadequate standard of care (SOC) energy support in the hospital leads to dietary energy deficiencies in BI patients. However, it is unclear how underfeeding (UF) affects protein synthesis post-BI.

Lactate as a myokine and exerkine: drivers and signals of physiology and metabolism.

No longer viewed as a metabolic waste product and cause of muscle fatigue, a contemporary view incorporates the roles of lactate in metabolism, sensing and signaling in normal as well as pathophysiological conditions. Lactate exists in millimolar concentrations in muscle, blood, and other tissues and can rise more than an order of magnitude as the result of increased production and clearance limitations. Lactate exerts its powerful driver-like influence by mass action, redox change, allosteric binding, and other mechanisms described in this article.

Fractional Gluconeogenesis: A Biomarker of Dietary Energy Adequacy in a Rat Brain Injury Model.

Patients treated for traumatic brain injury (TBI) are in metabolic crises because of the trauma and underfeeding. We utilized fractional gluconeogenesis (fGNG) to assess nutritional adequacy in ad libitum-fed and calorically-restricted rats following TBI. Male Sprague-Dawley individually housed rats 49 days of age were randomly assigned into four groups: ad libitum (AL) fed control (AL-Con, sham), AL plus TBI (AL+TBI), caloric restriction (CR) control (CR-Con, sham), and CR plus TBI (CR+TBI).

Tracing the lactate shuttle to the mitochondrial reticulum.

Isotope tracer infusion studies employing lactate, glucose, glycerol, and fatty acid isotope tracers were central to the deduction and demonstration of the Lactate Shuttle at the whole-body level. In concert with the ability to perform tissue metabolite concentration measurements, as well as determinations of unidirectional and net metabolite exchanges by means of arterial-venous difference (a-v) and blood flow measurements across tissue beds including skeletal muscle, the heart and the brain, lactate shuttling within organs and tissues was made evident. From an extensive body of work on men and women, resting or exercising, before or after endurance training, at sea level or high altitude, we now know that Organ-Organ, Cell-Cell, and Intracellular Lactate Shuttles operate continuously.

The blood lactate/pyruvate equilibrium affair.

The Lactate Shuttle hypothesis is supported by a variety of techniques including mass spectrometry analytics following infusion of carbon-labeled isotopic tracers. However, there has been controversy over whether lactate tracers measure lactate (L) or pyruvate (P) turnover. Here, we review the analytical errors, use of inappropriate tissue and animal models, failure to consider L and P pool sizes in modeling results, inappropriate tracer and blood sampling sites, and failure to anticipate roles of heart and lung parenchyma on L⇔P interactions.