Effects of moderate hyperoxia on oxygen consumption during submaximal and maximal exercise

The present study examined the effect of hyperoxia on oxygen uptake (V˙O₂) and on maximal oxygen uptake (V˙O_2max) during incremental exercise (IE) and constant work rate exercise (CWRE). Ten subjects performed IE on a bicycle ergometer under normoxic and hyperoxic conditions (30% oxygen). They also performed four 12-min bouts of CWRE at 40, 55, 70 and 85% of normoxic V˙O_2max (ex1, ex2, ex3 and ex4, respectively) in normoxia and in hyperoxia. V˙O_2max was significantly improved by 15.0 (15.2)% under hyperoxia, while performance (maximum workload, W _max) was improved by only +4.5 (3.0)%. During IE, the slope of the linear regression relating V˙O₂ to work rate was significantly steeper in hyperoxia than in normoxia [10.80 (0.88) vs 10.06 (0.66) ml·min^–1·W^–1]. During CWRE, we found a higher V˙O₂ at ex1, ex2, ex3 and ex4, and a higher V˙O₂ slow component at ex4 under hyperoxia. We have shown that breathing hyperoxic gas increases V˙O_2max, but to an extent that is difficult to explain by an increase in oxygen supply alone. Changes in metabolic response, fibre type recruitment and V˙O₂ of non-exercising tissue could explain the additional V˙O₂ for a given submaximal work rate under hyperoxia. Electronic Publication     

Biological balance of sodium and potassium

Summary The rhythm of renal sodium and potassium excretion was measured in 4-h-intervals in 12 subjects. Each person exhibited clear circadian variations of each variable with a maximum between 8 a.m. and 4 p.m. In each subject and for both circadian rhythms the oscillation mean was correlated to the range of oscillation (amplitude).Increase in sodium or potassium excretion during 1 day resulted in an increase of oscillation range. The oscillation means of sodium and potassium periodicity did not correlate.The properties of biological control systems with oscillating correcting variables are comparable to those of technical control systems. The significance of circadian rhythm for the control of electrolyte balance is indicated.     

Effects of aldosterone on lipid metabolism and renal oxygen consumption in the rat

Summary The plasma level of free fatty acids (FFA) in adrenalectomized rats increases by 50% after treatment with aldosterone (2 g/100 g rat).Lipolytic activity in peripheral fat tissue is lowered after adrenalectomy and doubles after in vivo administration of aldosterone to adrenalectomized rats (measured as free fatty acid release in vitro from epididymal fat tissue).Lypolysis of adipose tissue stimulated by the in vitro presence of ACTH also increases after in vivo administration of aldosterone.Incorporation of intravenously administered label from U¹⁴C-palmitate into total extractable lipid of renal tissue is augmented 3 h after aldosterone administration to adrenalectomized rats, while no increase of the radioactivity is observed in total lipid from liver tissue. Treatment with aldosterone does not affect the total lipid content of kidney or liver in adrenalectomized rats.The oxygen consumption rate of kidney cortex slices with lactate, -hydroxybuterate or acetoacetate as substrates is lowered after in vivo administration of aldosterone to adrenalectomized rats. With succinate, however, the respiratory rate of kidney slices increases after aldosterone treatment of adrenalectomized rats, the ouabain-sensitive respiration being more affected than the ouabain-insensitive respiration. An interpretation of the O₂ consumption data implicating competition of lipid metabolism for CoA-SH is discussed.     

心宁胶囊对犬心脏血流动力学及心肌耗氧量的影响

目的：研究心宁胶囊对麻醉开胸犬心脏血流动力学及心肌耗氧量的影响,探索其对心脏功能的药理作用及作用机制。方法：将20只犬随即分成模型组、阳性药物组、心宁胶囊高、低剂量组,观察麻醉犬冠状动脉血流量、心肌耗氧量和心率等指标的变化。结果：与模型组比较,心宁胶囊具有增加冠脉血流量、降低心肌耗氧量等作用（P〈0.05）。结论：心宁胶囊对犬心脏血流动力学及心肌耗氧量有调整和改善作用。     

Effects of three histaminergic compounds on function and oxygen consumption of isolated guinea-pig hearts

First experiences in man indicate, that even in catecholamine-insensitive congestive cardiomyopathy a considerable improvement of myocardial function can be attained by the H₂-receptor agonist impromidine. In an isolated, pressure-volume work performing guinea-pig heart preparation cardiac effects of three histaminergic compounds (N ,5-dimethylhistamine (HCl)₂, 5-ethyl-N -methyl-histamine (HCl)₂,N ,N -dimethyl-histamine (HCl)₂) were examined. Influences on function and myocardial oxygen consumption were compared to those obtained by impromidine.Dose-response curves for the histamine derivatives were 1.7–2.5 orders of magnitude right of the impromidine curves. Maximal inotropic stimulation was greater forN ,5-dimethyl-histamine (HCl)₂ than for impromidine. All compounds exhibited a high chronotropic effect and, at high concentrations, a net coronary dilating effect.     

Effects of agouti-related protein,orexin and melanin-concentrating hormone on oxygen consumption in mice

Neuropeptides in the hypothalamus play a pivotal role in the regulation of energy balance. Agouti-related protein (AGRP), orexin and melanin-concentrating hormone (MCH) have been identified in the hypothalamus as orexigenic peptides. This study was undertaken to investigate the effects of AGRP, orexin and MCH on oxygen consumption. Oxygen consumption was determined by an O2/CO2 metabolism measuring system at 22 degrees C. Mice were kept unrestrained in the chamber without food or water during the light cycle, and the oxygen consumption was measured for 2 h after intra-cerebroventricular (ICV) administration. ICV administered AGRP (1 nmol/mouse) significantly decreased oxygen consumption compared to ACSF-treated controls. Orexin (1 nmol/mouse) significantly increased oxygen consumption, while MCH (1 nmol/mouse) had no significant effect compared to ACSF-treated controls. These results suggest that AGRP, orexin and MCH might have different effects on energy expenditure, thereby regulating appetite and body weight.     

Effects of shortening velocity and of oxygen consumption on efficiency of contraction in dog gastrocnemius

Previous observations have shown that, in isolated perfused dog gastrocnemii in situ, stimulated to aerobic rhythmic isotonic tetanic contractions (at about 40% of maximal isometric force), only about 20% of the overall metabolic power (proportional to the rate of O₂ consumption, O₂) was converted into mechanical power (Ẇ). Here we report that, in the same preparation, the maximal velocity during the shortening phase of each tetanus (v, mm s^–1) increased with the rate of energy dissipation, as given by the difference between O₂ and Ẇ (W kg^–1). The relationship between these variables was described by: v=2.85(O₂–Ẇ)^1.24 (R ²=0.85; n=17). A mathematical analysis of this equation shows that the overall mechanical efficiency (=ẆO₂ ^–1) decreased with increasing v (at constant O₂), whereas it increased with increasing O₂ (at constant v). The net effect of this state of affairs was that the decrease of over the entire range of work intensities was relatively minor (from 0.22 to 0.15), in spite of a large increase of v, (from 40 to 120 mm s^–1), thanks to the concomitant increase of O₂ (from 10 to 25 W kg^–1). So, under these experimental conditions, the energetics of work performance seems to be governed by two conflicting needs. The need for a sufficiently high shortening speed (and hence power output), itself requiring a sufficiently large energy dissipation rate, which, however, brings about a fall in . This is counteracted by the increased O₂, which in turn leads to an increased efficiency at the expense of a fall in shortening speed.This article was published in Human Muscular Function during Dynamic Exercise, Marconnet P, Saltin B, Komi P, Poortmans J (eds) Med Sport Sci 41 (series editors: M. Hebbelink, R.J. Shephard) pp. 1–9, Karger, Basel, 1996. It is reproduced with minor editorial modifications. Permission from Karger is gratefully acknowledged.