Glucose-6-phosphate dehydrogenase activity in monolayer cultures of thyroid epithelial cells: TSH and inhibition of nitrogen oxide synthase affect the enzyme activity and the oxygen sensitivity of the histochemical assay

The objective was to investigate glucose-6-phosphate dehydrogenase (G6PD) activity in monolayer cultures of thyroid epithelial cells and to examine whether inhibition of nitric oxide synthase affects activity of G6PD or oxygen sensitivity of the assay. Primary cultures without TSH addition prior to experiments demonstrated a TSH-dependent increase in G6PD activity. G6PD activity was higher in F12 medium than in a serum-free physiological medium. Secondary cultures grown in F12 medium demonstrated a diminished activity of G6PD and a lack of response to TSH. In the serum-free physiological medium, G6PD activity was comparable to that found in primary cultures and a response to high concentrations of TSH was maintained. In primary cultures grown in F12 medium devoid of TSH, G6PD activity decreased dose-dependently when nitric oxide synthase activity was inhibited. The oxygen sensitivity of the assay was comparable to that reported previously in malignant cells and correlated with the activity of G6PD in primary cultures. We suggest that thyroid epithelial cells may be an appropriate system to investigate oxygen sensitivity of the G6PD assay as the cells demonstrate a reduced oxygen sensitivity which can be influenced by culture conditions.     

Learning,habituation, and training

Summary The apparent efficiency of sub-maximum exercise tends to be lower in subjects with a large aerobic power. This is probably an artefact arising from neglect of the oxygen debt in the calculation of mechanical efficiency. Changes in the extent of oxygen debt can obscure an increased skill of performance with training. Efficiency is improved by repetition of a given mode of exercise, but not by other forms of training. Habituation is greater during work than at rest, but even during work the change in pulse rate of young men does not exceed 2–5 beats/min over 5 experimental days. Habituation is lost if the test procedure is not repeated during training; this can complicate assessments of training from the response to sub-maximum exercise.     

Multiple sites of oxygen sensing and their contributions to hypoxic pulmonary vasoconstriction

Oxygen sensing by the pulmonary vasculature is important for the regulation of vessel tone and the matching of lung perfusion to ventilation. Airways hypoxia is a major stimulus for vasoconstriction, which diverts blood from hypoxic alveoli to better ventilated areas of the lung. Several hypotheses have emerged to explain how pulmonary arteries sense a decrease in oxygen and mediate hypoxic pulmonary vasoconstriction (HPV). They differ mainly in where they place the main site of HPV: in the endothelial or smooth muscle cells of the artery wall. HPV probably results from synergistic actions on both cell types, but it can proceed in the absence of endothelium, suggesting that the primary oxygen sensor is the smooth muscle cell and endothelium-derived agents modulate the muscle response. Several oxygen-sensing targets have been identified in smooth muscle, including potassium channels, Ca(2+) stores in the sarcoplasmic reticulum (SR) and the Ca(2+) sensitivity of the contractile proteins. The evidence for different oxygen-sensing mechanisms in pulmonary vessels is discussed.     

Validity of heart rate and ratings of perceived exertion as indices of exercise intensity in a group of children while swimming

Summary The purpose of this study was to investigate the validity of heart rate (f _c) and ratings of perceived exertion (RPE) as indices of exercise intensity in a group of children while swimming. Six healthy male swimmers, aged 10–12, swam tethered using the breast-stroke in a flume. The resistance started at 1.0 kg and increased in 1.0 kg steps up to the point of their exhaustion. The subjects swam for 5 min during each period, with a rest of 10–20 min until they had returned to their resting f _c level. The last exercise intensity was with the maximal mass the subjects could support for 2 min. The last min of oxygen consumption (VO₂) and 30 s of f _c were measured during each exercise period. The subjects gave their RPE assessment at the end of exercise.The individual relationships between f _c and VO₂, and percentage maximal oxygen consumption (% VO_2max, were linear with a high correlation r=0.962–0.996 and r=0.962–0.996, respectively. Therefore, it was concluded that f _c was valid as an index of the exercise intensity of children while swimming. Compared to the results found in adults using a similar protocol, the children's f _c were 8.3–26.9 beats·min^–1 higher than those of the adults at the given % VO_2max. The present study showed two different patterns in the relationship between VO₂ and RPE in individuals. In two subjects the RPE increased linearly with VO₂ while in the other four subjects the increase was discontinuous. If f _c and RPE were to be applied to the setting and evaluation of exercise intensity during swimming, it would seem that f _c would be a more useful guide than RPE for some children.     

Maximal oxygen consumption,pulmonary function,body composition,and anthropometry of adolescent female athletes

Three groups of girl athletes — 10 gymnasts and 8 middle-distance swimmers averaging 14 years of age, and 8 middle-distance runners averaging almost 19 — were the subjects of this study. The maximal oxygen intake was determined by graded work load on a bicycle ergometer, certain pulmonary functions by spirometry, and total body potassium by wholebody counting of naturally radioactive⁴⁰K. The total body water was obtained from measurements of deuterium oxide and application of the dilution principle, and creatinine excretion was determined from urine collections. Fat-free mass was calculated from total body water, and the amount of body fat was obtained by subtracting fat-free mass from body weight. Cell mass was calculated from total body potassium. Supporting evidence of leanness or fatness was provided by anthropometric measurements.The runners and swimmers achieved significantly higher maximal oxygen consumption per kg of body weight, fat-free mass, and cell mass; and the runners excelled the gymnasts in certain other pulmonary functions. Total body potassium in milliequivalents per kg of body weight, total body water expressed in percentage of body weight, and creatinine coefficients were similar in all three groups of subjects. These results indicated no differences in body composition. Calculations of body fat, fat-free mass, and cellular mass verified that conclusion; and supporting evidence was obtained from subcutaneous fat folds and from appraisal of leanness by corrected limb diameters or volumes, which also were similar in all three groups.     

Residual effects of prior exercise and recovery on subsequent exercise-induced metabolic responses

Abstract Data on the metabolic responses to repeated endurance exercise sessions are limited. Thus, the aims of this study were to examine (1) the impact of prior exercise on metabolic responses to a subsequent exercise session and (2) the effect of different recovery periods between two daily exercise sessions on metabolic responses to the second bout of exercise. Nine male elite athletes participated in four 25-h trials: one bout of exercise (ONE), two bouts of exercise separated by 3 h of rest and one meal (SHORT), two bouts of exercise separated by 6 h of rest and two meals (LONG), and a trial with no exercise (REST). All exercise bouts consisted of 10 min cycling at 50% followed by 65 min at 75% of maximal O₂ uptake. Compared to no prior exercise (ONE), a previous bout of exercise (SHORT) was followed by higher mean O₂ uptake, heart rate (HR), rectal temperature (T_R), excess post-exercise oxygen consumption and lower respiratory exchange ratio (R) during and after a similar exercise session 3 h later. A longer rest interval between the two exercise bouts (6 h versus 3 h) and an additional meal resulted in a decrease in O₂ uptake, HR, T_R and an increase in R during the second bout of exercise, but no effects on post-exercise metabolism were found. Thus, augmented metabolic stress was observed when strenuous exercise was repeated after only 3 h of recovery, but this was attenuated when a longer recovery period including an additional meal was provided between the exercise sessions.     

Methylglyoxal induces apoptosis mediated by reactive oxygen species in bovine retinal pericytes

One of the histopathologic hallmarks of early diabetic retinopathy is the loss of pericytes. Evidences suggest that the pericyte loss in vivo is mediated by apoptosis. However, the underlying cause of pericyte apoptosis is not fully understood. This study investigated the influence of methylglyoxal (MGO), a reactive alpha-dicarbonyl compound of glucose metabolism, on apoptotic cell death in bovine retinal pericytes. Analysis of internucleosomal DNA fragmentation by ELISA showed that MGO (200 to 800 microM) induced apoptosis in a concentration-dependent manner. Intracellular reactive oxygen species were generated earlier and the antioxidant, N-acetyl cysteine, inhibited the MGO-induced apoptosis. NF-kappaB activation and increased caspase-3 activity were detected. Apoptosis was also inhibited by the caspase-3 inhibitor, Z-DEVD-fmk, or the NF-kappaB inhibitor, pyrrolidine dithiocarbamate. These data suggest that elevated MGO levels observed in diabetes may cause apoptosis in bovine retinal pericytes through an oxidative stress mechanism and suggests that the nuclear activation of NF-kappaB are involved in the apoptotic process.     

Surface tension of animal cartilage as it relates to friction in joints

Measurements of the surface tension of articular cartilage and friction experiments were carried out to provide further evidence in support of a new theory regarding the mechanism of friction in joints. To determine the surface tension of cartilage, contact angle measurements were used in conjunction with the equation of state for interfacial tensions. The advancing contact angle between saline drops and articular cartilage was found to be 100°±5°, indicating a highly hydrophobic surface. The corresponding surface tension value was calculated to be 22.5 ergs/cm². Friction of cartilage against hydrophobic surfaces is shown to be lower than the friction of cartilage against hydrophilic surfaces. All these results further support the theory that lubrication by nonwetting drops occurs in joints and may be responsible for the exceptional friction characteristics of the joints.     

Thermogenesis and thermolysis during sleeping and waking in the rat

Thermogenesis (VO₂), sensible heat loss and subcutaneous back temperature were recorded simultaneously during sleeping and waking in both intact and depilated rats at Ta ranging from 21–28°C.VO₂ increased during wakefulness (W), decreased and plateaued during slow wave sleep (SWS) and then decreased 10% with each paradoxical sleep (PS) phase. Sensible heat loss, which represented about 90% of the heat production, increased and plateaued during SWS, decreased in W and generally rose abruptly (+40%) during PS. After removal of the fur the mean levels ofVO₂ and sensible heat loss were increased by 30–50% and returned to normal values within two weeks, although their variations related to stages of sleep were unchanged.These results concerning thermogenesis and thermolysis are in agreement with the variations of body temperature (brain excluded) during sleeping and waking.     

Energetics of karate kumite

It is speculated that anaerobic metabolism is the predominant source of energy in karate kumite. However, no experimental proof is currently available. The metabolic cost and fractions of aerobic and anaerobic energy of karate kumite fighting were investigated. Ten male nationally or internationally ranked karateka [means (SD) age 26.9 (3.8) years, height 1.80 (0.08) m, mass 77.2 (12.8) kg] performed two to four fights scheduled and judged like a championship. Oxygen uptake was measured continuously with a portable spirometric device. Blood lactate was determined immediately before, and minute by minute after, each fight. Aerobic, anaerobic alactic and anaerobic lactic energy were calculated from oxygen uptake during the fight (VO₂), the fast component of the post-fight oxygen uptake (VO_2PCr) above resting values and changes in blood lactate concentration (Net-BLC), respectively. Altogether, 36 fights lasting 267 (61) s were analysed. The referees decisions caused an activity-to-break ratio of approximately 2:1. VO₂, VO_2PCr, and Net-BLC per fight were 165.3 (52.4) ml^.kg^–1, 32.2 (7.2) ml^.kg^–1and 4.2 (1.9) mmol^.l^–1; the overall energy cost above rest was 334.3 (86.3) kJ per fight. Fractions of aerobic, anaerobic alactic, and lactic energy sources were 77.8 (5.8)%, 16.0 (4.6)%, and 6.2 (2.4)%, respectively. The results indicate a high metabolic rate in karate kumite. However, the acyclic activity profile implies that aerobic metabolism is the predominant source of energy and there is anaerobic supplementation, mainly by high-energy phosphates.