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PubMed1985

Enhanced oxygen consumption in adrenal medulla on stimulation with acetylcholine.

When perfused cortex-free ox adrenal medulla was stimulated to secrete catecholamine by infusion of 0.1 mM acetylcholine for 4 min, the oxygen consumption increased to a value which was 0.15 +/- 0.07 mumole O2/min/g wet weight (+/- S.D., N = 12) above the pre-stimulation value of 0.49 +/- 0.15 (P less than 0.001). 1.4 +/- 0.9 (+/- S.D., N = 12) mole of catecholamine was secreted per mole of enhanced O2 consumption in the 16 min following the start of the stimulation. The rate of ATP hydrolysis by the proton-translocating Mg-ATPase of the chromaffin granule may increase on fusing with the plasma membrane of the chromaffin cell during exocytosis. However, from the amount of catecholamine secreted, this was estimated to account for less than 17% of the oxygen consumption increase. The amount of catecholamine secreted by 4 min 0.1 mM acetylcholine stimulations correlated with the enhancement of oxygen consumption (r = 0.82, P less than 0.001) but, on stimulation with 60 microM veratridine for 4 min, O2 consumption enhancement was anomalously low. This dependence on mode of stimulation suggests that ATP consumption in exocytosis itself is an inadequate explanation. Ouabain-sensitive oxygen consumption rose from undetectable levels to 18 +/- 8% (+/- S.D., N = 4) of the basal respiration during prolonged 0.1 mM acetylcholine stimulation in the absence of Ca, indicating that Na,K-ATPase was not responsible for all of the oxygen consumption enhancement.

Acetylcholine↗

PubMed1984

Oxygen consumption in collagenase-liberated rat adipocytes in relation to cell size and age.

Oxygen consumption of collagenase-liberated rat adipocytes was measured by two different techniques: a microspectrophotometric method using hemoglobin as indicator of respiration and a technique using the oxygen electrode. These two completely different techniques gave similar values for oxygen consumption. With the spectrophotometric method, the oxygen consumption of single fat cells was determined. A close positive correlation (r = greater than 0.90) between oxygen consumption and fat cell size was observed in each tissue examined. With the oxygen electrode technique, oxygen consumption of adipocyte suspensions from young (40 days, 180 g) and old (90 days, 480 g) rats was examined. Fat cells of the suspensions were separated into classes of different size by a flotation technique. A significant positive correlation between fat cell size and oxygen consumption was observed in both young (r = 0.88) and old (r = 0.95) rats. However, the slope was much steeper in young rats. At a cell weight of 0.1 microgram the oxygen consumption was 0.364 and 0.086 microL O2/10(6) cells/min-1 in young and old rats, respectively. In the literature, a number of separate metabolic pathways have been found to be related positively to fat cell size and negatively to age. We conclude that these scattered metabolic observations are in agreement with integrated data on energy expenditure as evaluated from oxygen consumption. Estimations of the energy expenditure of adipose tissue indicates that this tissue is responsible for about 1% and 0.5% of the total energy expenditure in young and old rats, respectively.

Adipose Tissue↗

PubMed1980

Differential effects of prostaglandins and arachidonic acid on gastric circulation and oxygen consumption.

Experiments were carried out on anesthetized dogs to compare the effects of prostaglandin E2 (PGE2), prostacyclin (PGI2) and arachidonic acid (AA) administered intraarterially on gastric blood flow and oxygen consumption during constant arterial pressure perfusion and constant flow perfusion of the stomach. Both PGE2 and PGI2 increased total blood flow and oxygen consumption both in the resting stomach and following histamine stimulation although the effects of PGE2 on the oxygen consumption in stimulated stomach were not statistically significant. On the contrary, AA decreased both gastric blood flow and oxygen consumption in the histamine stimulated stomach. To determine if these compounds can influence gastric oxygen consumption independently of their effects on blood flow, the experiments with constant flow perfusion were performed. Both PGE2 and PGI2 decreased both the perfusion pressure and oxygen consumption in the resting as well as in the histamine-stimulated stomach whereas AA increased perfusion pressure and decreased oxygen consumption during histamine administration. Effects of AA were blocked by indomethacin suggesting that not AA itself but some of its metabolites, most likely thromboxanes were responsible for the hemodynamic and metabolic changes resulting from the contraction of gastric arterioles and precapillary sphincters. On the contrary, both PGE2 and PGI2 caused gastric hyperemia and an increase in oxygen consumption in the resting stomach, but decreased the latter parameter in the stimulated stomach, most probably as a result of secretory inhibition overcoming direct vascular effects of these compounds.

Animals↗

PubMed1988

Effects of temperature on the oxygen consumption in thin slices from different brain regions.

The oxygen consumption of brain slices from 12 different regions of the guinea pig brain was measured and the effects of temperature on the consumption was investigated. At 37 degrees C the oxygen consumption in cerebral gray matter and inferior colliculus was higher than that of other regions, whilst the consumption in cerebral white matter and brainstem was approximately half of that in cerebral gray matter. In any region lowering the tissue temperature from 37 to 28 degrees C reduced the oxygen consumption by 6-8% of the value obtained at 37 degrees C per one degree. At 21 degrees C the consumption was decreased to 15% of the value obtained at 37 degrees C. It is notable that the consumption in hippocampal slices tested was remarkably increased by raising the temperature up to 50 degrees C and no consumption was observed at 55 degrees C.

Animals↗

PubMed1991

Oxygen consumption stimulated by increases in permeability of Na+ of mouse diaphragm muscle in vitro.

1. The effects on oxygen consumption of agents that modify Na(+)-permeability were examined in mouse diaphragm muscle perfused with a bathing solution that contained (+)-tubocurarine in a flow-through mode. Twitch tension and levels of Na+ and K+ in the muscle were also measured. 2. Unstimulated preparations decreased the concentration of oxygen in the bathing solution, indicating a basal level of oxygen consumption. Electrical stimulation of the muscle further decreased the concentration of oxygen. Potassium cyanide eliminated both the basal and the stimulated consumption of oxygen. 3. Veratridine facilitated the effect of stimulation at 0.1 Hz on both the consumption of oxygen and the twitch tension. Ouabain antagonized those effects. 4. Twitch contractions were blocked in the presence of dantrolene sodium or by pretreatment with ethylene glycol. Electrical stimulation of such preparations still caused a residual but considerably decreased consumption of oxygen. Ouabain and tetrodotoxin reduced the residual consumption of oxygen. 5. Ouabain significantly increased the levels of Na+ in the tissue, while veratridine alone did not. The effect of ouabain was further potentiated by the simultaneous presence of veratridine. 6. These results indicate that the enhancement of the sarcolemmal permeability to Na+ increases the rate oxygen consumption. This concept supports the hypothesis that Na+ homeostasis depends on energy consumption.

Animals↗

PubMed1993

Acute effects of dobutamine on myocardial oxygen consumption and cardiac efficiency measured using carbon-11 acetate kinetics in patients with dilated cardiomyopathy.

OBJECTIVES: The aim of this study was to use positron emission tomography (PET)-derived carbon (C)-11 acetate kinetics to determine the effects of dobutamine on oxidative metabolism and its effects on myocardial efficiency in a group of patients with dilated cardiomyopathy. BACKGROUND: Dobutamine is known to improve myocardial function but may do so at the expense of myocardial oxygen consumption, which could be a potential deleterious effect. Carbon-11 acetate kinetics correlate with myocardial oxygen consumption as shown in animal models. Combining these scintigraphic measurements of oxygen consumption with estimates of cardiac work results in a work-metabolic index, which reflects cardiac efficiency. METHODS: Eight patients with nonischemic dilated cardiomyopathy underwent dynamic PET imaging, echocardiography and hemodynamic measurements. Seven of these patients were also studied while receiving dobutamine. Direct measurements of myocardial oxygen consumption using coronary sinus catheterization were obtained with eight of the PET studies to validate C-11 acetate in patients with cardiomyopathy. RESULTS: The mean (+/- SD) C-11 clearance rate significantly increased with dobutamine from 0.105 +/- 0.027 to 0.155 +/- 0.023 min-1 (p = 0.001). Directly measured myocardial oxygen consumption had a linear relation to the mean C-11 clearance rate (r = 0.8, p = 0.018). Dobutamine was noted to significantly reduce systemic vascular resistance as well as the severity of mitral regurgitation. The work-metabolic index determined using hemodynamic variables and PET data increased from 2 +/- 0.7 x 10(4) to 2.6 +/- 0.6 x 10(4) (p = 0.04). Efficiency, estimated by employing the oxygen consumption to k2 relation, also increased from 13 +/- 4.5% to 16.9 +/- 6.4% (p = 0.04). CONCLUSIONS: Despite an increase in myocardial oxygen consumption, dobutamine led to an increase in work-metabolic index in patients with dilated nonischemic cardiomyopathy. Dobutamine reduced systemic vascular resistance and mitral regurgitation, suggesting that in this group of patients, it had important vasodilatory action in addition to its inotropic effects. The use of the C-11 acetate PET for determining myocardial oxygen consumption and estimating efficiency could potentially complement existing clinical measures of ventricular performance and may allow improved and objective evaluation of therapy in patients with heart failure.

Adult↗

PubMed1993

Effects of guanfacin and nitroprusside on the haemodynamics and oxygen consumption of Brahman steers.

1. The systemic vascular resistance (SVR) and oxygen consumption of high grade Brahman (Bos indicus) steers were measured before and after treatment with guanfacin and nitroprusside to test whether the decreased whole-body oxygen consumption seen with guanfacin treatment is due to less oxygen consumption by vascular smooth muscle. 2. Guanfacin changed oxygen consumption by -31% but raised SVR by 61%. Nitroprusside had no significant effect on oxygen consumption but changed SVR by -20%. Moreover, with guanfacin, the changes in oxygen consumption and SVR were temporally incongruent. 3. We conclude that the lowered whole-body oxygen consumption caused by guanfacin was not due to decreased consumption by vascular tissue.

Animals↗

PubMed1993

Oxygen kinetics during liver transplantation: the relationship between delivery and consumption.

In anesthetized humans, oxygen consumption is independent of oxygen delivery above a critical threshold. Below this critical level, lactic acid is a marker of anaerobic metabolism and tissue oxygen debt, and heralds a supply dependency of oxygen consumption. The goal of this study was to determine whether a threshold value for oxygen delivery below which oxygen consumption becomes supply dependent can be identified in patients with normal, impaired, or absent liver function. Measurements were made in 34 surviving patients (group 1) and in 16 nonsurvivors with sepsis and postoperative liver graft failure (group 2). Hemodynamic measurements and blood samples were taken 10 minutes after introduction of anesthesia, 10 minutes after cross-clamping, and 10 minutes after reperfusion of the new liver. At these time points, we measured blood lactate, cardiac output, and arterial and mixed venous oxygen contents in order to calculate oxygen consumption and oxygen delivery. In both groups, cardiac output, oxygen delivery, and oxygen consumption decreased during the anhepatic phase and increased after unclamping of the inferior vena cava. Lactate increased in both groups during surgery, but was significantly higher in nonsurvivors (6.6 +/- 0.4 mmol/L) than in survivors (4.6 +/- 0.1 mmol/L) (P < .05). With similar changes for oxygen delivery and oxygen consumption during increased lactate levels we could not identify a clear supply dependency of oxygen consumption in survivors and nonsurvivors during liver transplantation. We conclude that the interpretation of blood lactate levels during circulatory shock can be biased due to a reduced lactate clearance in patients with impaired liver function, unrelated to the status of the relationship between oxygen delivery and consumption.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2026

Prediction of alcohol consumption: The role of genetics, impulsivity, and sensation seeking from adolescence to adulthood.

BACKGROUND: There are well-known phenotypic and genetic associations among impulsivity, sensation seeking (SS), and alcohol consumption, but whether they vary between adolescence and early adulthood remains unclear. PURPOSE/HYPOTHESES: We hypothesized that adolescent alcohol consumption would be better predicted by polygenic indices (PGIs) of impulsivity and SS than PGIs of adult alcohol consumption (drinks per week; DPW), but that the reverse would be observed in young adulthood (i.e., stronger associations for DPW PGIs). METHODS: N = 733-754 twins of European genetic ancestry from the Colorado Longitudinal Twin Study were assessed at age 17 and/or 23 years using structural equation modeling. RESULTS: The SS PGIs were associated with alcohol consumption in adolescence (β=0.16), whereas DPW PGIs were associated with alcohol consumption in early adulthood (β=0.15). Additionally, phenotypic measures of impulsivity and SS are associated with alcohol consumption at both ages (β=.13-.21) and mediated some PGI-alcohol associations. DISCUSSION: These findings suggest that genetic influences on alcohol consumption change from adolescence to early adulthood, with genetic influences on sensation seeking most relevant to alcohol consumption in adolescence.

Humans↗

PubMed1996

Effects of acute and chronic ethanol administration on hepatic hemodynamics and hepatic oxygen consumption in awake rats.

BACKGROUND/AIMS AND METHODS: We investigated the effects of acute and chronic ethanol administration on hepatic hemodynamics and hepatic oxygen delivery and consumption in awake rats, using the radiolabeled microsphere technique and measurement of oxygen content in blood. RESULTS: Acute oral and intraarterial ethanol administration produced a significant increase in liver blood flow and hepatic oxygen delivery, but resulted in a significant (25-41%) decrease in hepatic oxygen consumption. These changes lasted up to 5 h after ethanol administration. At 24 h, hepatic oxygen consumption was significantly increased by 33% over control values. During withdrawal in rats fed liquid diets containing alcohol for 6 weeks, hepatic oxygen delivery was maintained at the same level as control pair-fed rats, while hepatic oxygen consumption increased by 28%. Further, in abstinent rats, acute ethanol readministration resulted in a 41% increase in hepatic oxygen delivery but a 32% decrease in hepatic oxygen consumption. CONCLUSIONS: These findings demonstrate, in awake animals, a biphasic response of hepatic oxygen consumption following acute ethanol administration and an increase in hepatic oxygen consumption following chronic ethanol intake. Furthermore, acute ethanol treatment reduced hepatic oxygen consumption in spite of an increase in hepatic oxygen delivery.

Animals↗

PubMed2001

Comparison of myocardial oxygen consumption using 11C acetate positron emission tomography scanning in a working and non-working heart transplant model.

OBJECTIVE: In acute cardiac rejection, changes in myocardial oxygen consumption occur; non-invasive detection of these metabolic changes would have obvious clinical utility. In the classic cervical, heterotopic, canine, transplant model, the heart is non-working. It has a low myocardial oxygen consumption. Creation of a working model with normal myocardial oxygen consumption would enhance validity of non-human studies. METHODS: Clearance of 11C acetate was determined by positron emission tomography (PET) scanning and compared with myocardial oxygen consumption in normal and transplanted canine hearts. Donor hearts from mongrel dogs (2.5-3 kg; n=4) were transplanted into the neck of adult beagles (12-15 kg; n=4), no immunosuppression was given. Two non-working hearts were modified to eject only coronary flow via the right ventricle. In two hearts, a novel working model was created with aortic regurgitation to load the left ventricle. Working and non-working hearts underwent PET scanning on post-operative days 2 and 4. Normal dog hearts (n=2) and native hearts of transplanted dogs (n=3) were used to validate the scanning technique. Coronary sinus and aortic oxygen saturation data along with myocardial blood flow (radiolabeled microspheres) confirmed that clearance of 11C acetate in normal and transplanted hearts followed a bi-exponential model. RESULTS: Myocardial oxygen consumption was correlated with the rate constant of 11C acetate rapid phase clearance (r=0.91) in normal and transplanted hearts. The working hearts had increased myocardial oxygen consumption compared to non-working hearts. CONCLUSIONS: This study (1) introduces a model of a working heterotopic cardiac transplantation with near-normal oxygen consumption; and (2) demonstrates that regional myocardial oxygen consumption in transplanted hearts can be detected by 11C acetate PET.

Acetates↗

PubMed1998

Effects of percutaneous balloon mitral valvuloplasty and exercise training on the kinetics of recovery oxygen consumption after exercise in patients with mitral stenosis.

AIMS: Kinetics of recovery oxygen consumption after exercise plays an important role in determining exercise capacity. This study was performed to assess the kinetics of recovery oxygen consumption in mitral stenosis and evaluate the effects of percutaneous balloon mitral valvuloplasty and exercise training on the kinetics. METHODS AND RESULTS: Thirty patients with mitral stenosis (valve area < or =1.0 cm2) and same sized age- and size-matched healthy volunteers were included for this study. All subjects performed maximal upright graded bicycle exercise. Thirty consecutive patients who underwent successful percutaneous balloon mitral valvuloplasty (valve area > or =1.5 cm2 and mitral regurgitation grade < or =2), were randomized to an exercise training group or non-training group. The exercise group performed daily exercise training for 3 months. Half-recovery time of peak oxygen consumption was significantly delayed in mitral stenosis as compared to normal subjects (120+/-42 s vs 59+/-5, P<0.01). Peak oxygen consumption (ml x min(-1) x kg(-1)) was significantly increased in both the training (16.8+/-4.9 to 25.3+/-6.9) and non-training groups (16.3+/-5.1 to 19.6+/-6.0) 3 months after percutaneous balloon mitral valvuloplasty. Half-recovery time of peak oxygen consumption was significantly shortened in the training group (124+/-39 to 76+/-13, P<0.01), but not in the non-training group (114+/-46 to 109+/-44 s, P=0.12) at 3 months follow-up. The degrees of symptomatic improvement after percutaneous balloon mitral valvuloplasty were more closely correlated with the changes of the half-recovery time of peak oxygen consumption than those of peak oxygen consumption. CONCLUSION: Kinetics of recovery oxygen consumption was markedly delayed in mitral stenosis, which was improved after exercise training but not after percutaneous balloon mitral valvuloplasty alone. These results suggest that adjunctive exercise training may be useful for improvement of recovery kinetics and subjective symptoms after percutaneous balloon mitral valvuloplasty.

Adult↗

PubMed1989

Effect of level of nutrition on splanchnic blood flow and oxygen consumption in sheep.

The objective of the present study was to measure changes in splanchnic blood flow and oxygen consumption in sheep fed on a high-concentrate diet ad lib. (ADLIB) or an amount sufficient to maintain body-weight (MAINT) for 21 d. Eleven ram lambs were surgically implanted with chronic indwelling catheters in the portal, hepatic and mesenteric veins and mesenteric artery to measure blood flow and net O2 flux through the liver and portal-drained viscera (PDV). During the 21 d period, PDV (P less than 0.05) and liver (P less than 0.01) blood flow increased in ADLIB and decreased in MAINT lambs (treatment x day, linear). After 21 d, O2 consumptions in PDV and liver of MAINT lambs were 37 and 63% lower than in ADLIB lambs. In the control period, total splanchnic tissues represented an average of 52% of whole body O2 consumption. After 21 d, the relative contributions of PDV and liver to whole-body O2 consumption were 28 and 41% in ADLIB and 19 and 22% in MAINT lambs respectively. Allometric regression variables indicate that liver O2 consumption responds more rapidly to changes in metabolizable energy intake than portal O2 consumption. These results indicate that blood flow and O2 consumption in both PDV and liver are related to level of nutrition. Furthermore, splanchnic tissues represent a significant component of whole-body O2 consumption that is subject to manipulation by level of nutrition.

Animal Nutritional Physiological Phenomena↗

PubMed1995

Multivariate determinants of early postoperative oxygen consumption in elderly patients. Effects of shivering, body temperature, and gender.

BACKGROUND: Previous investigators have proposed that postoperative shivering may be poorly tolerated by patients with cardiopulmonary disease because of the associated significant increase in total-body oxygen consumption. However, the often-quoted 300-400% increase in oxygen consumption with shivering was derived from relatively few studies performed in a small number of younger persons specifically selected on the basis of clinically recognizable shivering. We hypothesized that the average elderly postoperative patient has a shivering response that is associated with a relatively small increase in total-body oxygen consumption. METHODS: One hundred eleven elderly patients (age > 60 yr) undergoing surgery were studied to assess the determinants of shivering and total-body oxygen consumption in the early postoperative period. Anesthetic technique, postoperative analgesia, and thermal management were controlled by protocol. The clinical variables associated with shivering and increased total-body oxygen consumption were determined by univariate and multivariate analyses. RESULTS: Mean total-body oxygen consumption in shivering patients was 38% greater than in nonshivering patients. Regardless of whether data from shivering patients were included in the analysis, oxygen consumption was directly proportional to mean body temperature. Despite similar core temperatures, men had a greater incidence of clinically recognizable shivering and greater total-body oxygen consumption than did women. CONCLUSIONS: The metabolic demands associated with postoperative shivering in elderly patients are less than those reported previously in younger persons. These findings suggest that if hypothermia predisposes to cardiovascular complications in the postoperative period, these complications are not likely to be mediated by shivering and increased metabolism.

Aged↗

PubMed1999

Factors influencing the individual effects of blood transfusions on oxygen delivery and oxygen consumption.

OBJECTIVE: To determine factors influencing the individual effects of blood transfusions regarding oxygen delivery and consumption. DESIGN: Chart review. SETTING: A university hospital cardiosurgical intensive care unit. PATIENTS: Sixty-seven patients with 170 transfusion events evaluated. INTERVENTIONS: Blood transfusion. MEASUREMENTS AND MAIN RESULTS: Measurements were performed before and after a blood transfusion, separated by 302 +/- 13 mins (mean +/- SEM). The individual increase in cardiac index resulting from a blood transfusion was inversely related to cardiac index before transfusion (p < .001), oxygen delivery index before transfusion (p < .001), and oxygen consumption index before transfusion (p < .001). The individual increase in oxygen delivery index was inversely related to oxygen consumption index before transfusion (p < .001). The individual increase in oxygen consumption index was inversely related to oxygen consumption index before transfusion (p < .001). Individual changes in cardiac index, oxygen delivery index, and oxygen consumption index were not significantly related to preoperative ejection fraction (25%-87%), age (32-81 yrs), and pretransfusion hemoglobin concentration (5.0-11.8 g/dL). CONCLUSION: In adult patients after cardiovascular surgery, oxygen delivery- and oxygen consumption-related variables predict the individual response to blood transfusions better than do patient characteristics such as preoperative ejection fraction, age, and pretransfusion hemoglobin concentration. Including oxygen delivery and oxygen consumption, variables into the transfusion decision, thus, may enable a more individual use of allogeneic blood in specific situations.

Adult↗

PubMed2006

Oxygen consumption, assessed with the oxygen absorption spectrophotometer, decreases independently of venoconstriction during hepatic anaphylaxis in perfused rat liver.

Anaphylactic shock is accompanied by a decrease in oxygen consumption. However, it is not well known whether oxygen consumption decreases during local anaphylactic reaction in liver. We determined the effects of anaphylaxis and norepinephrine on oxygen consumption in isolated rat livers perfused portally and recirculatingly at constant flow with blood (hematocrit, 12%). Oxygen consumption was continuously measured by monitoring the portal-hepatic venous oxygen saturation differences using the absorption spectrophotometer, the probes of which were built in perfusion lines. Hepatic anaphylaxis was induced by an injection of ovalbumin (0.01 or 0.1 mg) into the perfusate of the isolated liver of the rat sensitized with subcutaneous ovalbumin (1 mg). Hepatic venoconstriction and liver weight loss were similarly observed in response to norepinephrine (0.01-10 micromol L(-1)) and anaphylaxis. However, hepatic anaphylaxis reduced oxygen consumption, whereas norepinephrine increased it. There was a possibility that anaphylactic venoconstriction could reduce the perfused surface area, resulting in decreased oxygen consumption. However, pretreatment with a vasodilator of sodium nitroprusside substantially attenuated venoconstriction but not the decrease in oxygen consumption during anaphylaxis. Thus, we conclude that local hepatic anaphylaxis decreases oxygen consumption independently of venoconstriction in isolated blood-perfused rat livers.

Anaphylaxis↗

PubMedDate not supplied

Statistical evidence that endogenous reverse triiodothyronine (rT3) may affect oxygen consumption in food deprived chickens.

Exogenous rT3 decreases O2 consumption in mammals and birds. Until now a correlation coefficient and a regression equation have not been presented. Statistical evaluation seems to be requisite for verifying the answer to the question of whether endogenous rT3 may be able to reduce O2 consumption in birds where the normal level of plasma rT3 is 10 times less than the corresponding level of T3. Food deprived chickens (for 48 h) were used in this study because fasting enhances plasma rT3. The results revealed a reciprocal relation of T3 and rT3 in the circulation. Reverse T3 began to increase when T3 decreased to a plateau at 53.9% of initial level. As expected a reciprocal relationship was obtained (r = -0.749; n = 36) between plasma rT3 and O2 consumption. The regression line was calculated according to the equation: Y = -0.388X + 0.856. This relation differs from the linear relationship between T3 and O2 consumption (r = 0.796; Y = 0.107X + 0.449). The regression line lies in the range of 0.122-0.778 nmol rT3/l, which is found in some physiological conditions in birds where elevated plasma rT3 occurs. This suggests that endogenous rT3 may participate in modifying O2 consumption in birds. Using the rT3:T3 ratio the correlation coefficient was somewhat higher (r = -0.831; Y = -0.673X + 0.831) suggesting common involvement of both triiodothyronines in the reduction of O2 consumption during food deprivation. The drop in O2 consumption after 48 h of food deprivation was 28.4%; decreased T3 and increased rT3 may participate in 15.4% and 13.0% of this fall, respectively. The hypometabolic effectiveness of rT3 seems to be greater than the hypermetabolic effectiveness of T3, since a smaller increase of plasma rT3 was needed to reduce O2 consumption compared to the amount of T3 necessary to enhance it.

Animals↗

PubMed1993

Resting oxygen consumption in rats during food restriction, starvation and refeeding.

Oxygen consumption was measured in male rats during starvation and during different regimens of restricted feeding and refeeding after starvation. Changes in oxygen consumption and body mass were mostly parallel, but rats with a very reduced food intake displayed the same reduction in oxygen consumption as starved rats, despite the smaller reduction in body mass. Also, rats fed different amounts of food after starvation had different oxygen consumptions, but displayed the same changes in body mass. Two different refeeding regimens with restricted food amounts either induced a further depression of oxygen consumption (i.e. below starvation oxygen consumption), or a stabilizing of oxygen consumption on the level of starvation. The changes in oxygen consumption during restriction and feeding after starvation indicate that reductions in resting metabolic rate may not always be predicted from either body mass change or food intake.

Animals↗