Brain and blood lactate during acute and prolonged respiratory acidosis and alkalosis.
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Acid-Base Equilibrium↗
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Results for “Lactation, Prolonged”
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Influence of maternal diet on plasma-prolactin levels during lactation.
An improvement in maternal diet produced significant reductions in plasma-prolactin concentration at all stages of lactation. The prolonged high prolactin concentrations found in undernourished mothers may ensure milk synthesis when food intake is limited, by preferentially channelling nutrients towards the breast. The lower hormonal levels associated with improved maternal nutrition may shorten the period of post-partum infertility despite prolonged breast-feeding.
Amenorrhea↗
Splanchnic removal of lactate and pyruvate during prolonged exercise in man.
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Abdomen↗
Relationship between the lactate and ventilatory thresholds during prolonged exercise.
The anaerobic threshold is commonly measured by either blood lactate (lactate threshold) or ventilatory gases (ventilatory threshold); however, the relationship between these 2 methods is not conclusive. The lactate threshold has been characterised at either a fixed or variable blood lactate concentration (BLa). Recent studies have indicated a specific blood lactate concentration for each individual which considers the interindividual variations in lactate kinetics (individual anaerobic threshold), following either a continuous, exponential pattern or a discontinuous, threshold-like response. The ventilatory threshold is assessed using a variety of ventilatory parameters, many of which exhibit a threshold-like response during progressive exercise. Despite the apparent causal relationship between the stimulation of the ventilatory chemoreceptors and ultimately the ventilatory response and the accumulation of protons in the circulating blood, evidence does exist which refutes such a connection. Such evidence supporting a coincidental relationship examines no significant change in ventilation with significant increases in blood lactate concentration. Conversely, evidence from patients with McArdle's disease indicates that although no lactic acid is produced, these individuals do experience a threshold-like ventilatory response during incremental exercise. The ability to perform at the anaerobic threshold is now recognised as an integral component of endurance events. Several studies have concluded that the ventilatory threshold is highly correlated with endurance performance, in distances ranging from 26 miles (41.6 km) [r = -0.94] to 5 and 10 km (r = -0.945). The lactate threshold, in particular the individual anaerobic threshold, has been examined from a performance standpoint. Much of the literature supports the individual anaerobic threshold as the exercise intensity at which performance is maximal and able to be sustained for at least 50 minutes. With the variety of techniques utilised in assessing the anaerobic threshold, caution should be taken in interpretation of the results as the different protocols may elicit a variety of responses during incremental exercise. Furthermore, it is essential to account for the individual's unique response to such exercise.
Anaerobic Threshold↗
Lactate elimination in man: effects of lactate concentration and hepatic dysfunction.
Lactate elimination was studied in twenty-six healthy volunteers during primed constant lactate infusion or multiple lactate injection tests, at blood lactate concentrations of 1-8 mmol-1. Although lactate elimination fitted a single exponential curve over a 30 min period, a significant correlation between the rate removal constant (KL) and the peak blood lactate concentration (Lphi) was demonstrated: loge KL = -2.43-0.132 Lphi (P = 0.003, r = 0.63, n = 20) This suggests that lactate removal does not follow first order kinetics over a wide concentration range but becomes saturated at relatively low blood lactate concentrations. Estimates of the lactate distribution volume did not differ significantly at different dosage levels, but remained in the range 270-300 ml kg-1. Skeletal muscle uptake accounted for about 26% of the infused lactate load. Seven patients with well-compensated hepatic cirrhosis were compared with a group of six control subjects during primed constant infusion tests. Fasting and steady state blood lactate concentrations achieved were similar in both groups. A significant prolongation in lactate half-life was demonstrated in the cirrhotics (18.8 +/- 1.4 min (mean +/- SEM) compared to 14.7 +/- 2.2 min; P less than 0.02). Since peripheral uptake of lactate in the forearm was similar in the two groups, this suggests that hepatic lactate uptake was impaired, due either to hepatocyte dysfunction or portal diversion.
Adult↗
Splanchnic and peripheral glucose and lactate metabolism during and after prolonged arm exercise.
Splanchnic and peripheral exchange of glucose and gluconeogenic substrates was examined in 12 healthy subjects during 2 h of arm or leg exercise on a bicycle ergometer and during a 40-min postexercise recovery period. The work intensity corresponded to 30% of the maximal pulmonary oxygen uptake. The regional exchange of substrates was evaluated using catheter technique and indicator dilution methods for blood flow measurements. Our findings indicate that prolonged arm exercise as compared with exercise with the legs results in a greater increase in heart rate (25-40%) and a more marked reduction in splanchnic blood flow (10-30%) as well as higher arterial concentrations of lactate, free fatty acids, and catecholamines. The respiratory exchange ratio was consistently higher with arm exercise. In addition, arm exercise results in a greater fractional extraction and utilization of glucose by exercising muscle as well as a greater hepatic gluconeogenesis from lactate and glycerol. During recovery from prolonged arm exercise, leg muscle becomes an important site of lactate release to the splanchnic bed, despite a lack of net glucose uptake by the leg. Simultaneously, arm muscle shows an increase in glucose uptake in the absence of a net release of lactate. These coincident but discordant processes in the leg and arm during recovery suggest the occurrence of a redistribution of muscle glycogen from previously resting (leg) muscle to previously exercising (arm) muscle.
Adult↗
Dynamics of hepatic lactate and glucose balances during prolonged exercise and recovery in the dog.
The present experiments were undertaken to assess dynamics of hepatic lactate and glucose balance in the over-night-fasted dog during 150 min of moderate-intensity treadmill exercise and 90 min of exercise recovery. Catheters were implanted chronically in an artery and portal and hepatic veins 16 days before experimentation. 3-3H-glucose was infused to determine hepatic glucose uptake, as well as tracer-determined glucose production by isotope dilution (Ra). At rest, net hepatic lactate output was 0.33 +/- 0.15 mg.kg-1.min-1 and increased to 2.26 +/- 0.82 mg.kg-1.min-1 after 10 min of exercise, after which it fell such that the liver was a net lactate consumer by the end of exercise and through recovery. In contrast to the rapid release of lactate, net hepatic glucose output rose gradually from 2.58 +/- 0.20 mg.kg-1.min-1 at rest to 8.87 +/- 0.85 mg.kg-1.min-1 after 60 min of exercise, beyond which it did not change significantly until the cessation of exercise. Hepatic glucose uptake at rest was 1.38 +/- 0.42 mg.kg-1.min-1 and did not change appreciably during exercise or recovery. Absolute hepatic glucose output (net glucose output plus uptake) rose from 3.96 +/- 0.45 mg.kg-1.min-1 at rest to 10.20 +/- 1.09 mg.kg-1.min-1 after 60 min of exercise and was 9.65 +/- 1.15 mg.kg-1.min-1 at 150 min of exercise. Ra rose from 3.34 +/- 0.21 mg.kg-1.min-1 to 7.58 +/- 0.73 and 8.59 +/- 0.77 mg.kg-1.min-1 at 60 and 150 min, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Freezing provides a viable method for the prolonged, stable storage of blood lactate.
The only major methodological problem associated with the enzymatic determination of blood lactate levels is the stability of the metabolite in the perchloric acid supernatant. The data from this study show that freezing the protein-free supernatant provides a viable method for the prolonged, stable storage of blood lactate.
Freezing↗
Endocrine bases of lactational anoestrus in the sow.
Parturition in the sow is followed by a period of anovulation which is prolonged by lactation. Follicular development and luteinizing hormone (LH) secretion are depressed during the last month of pregnancy. After parturition, LH secretion increases but is again inhibited by the establishment of lactation. Lactating sows are submitted to stimuli originating from the young, whose intensity culminates 3-14 d post-partum (pp), and to high nutrient requirements for milk production. The inhibitory effects of sucklings are imposed during the first 3 d pp and seem to be mediated by the action of opioids at the hypothalamic level. The nutritional deficit constitutes an additional inhibitory factor. As lactation continues, LH secretion progressively increases. A further rise in LH occurs at weaning. Variations in follicle-stimulating hormone (FSH) profiles are less marked. The divergence observed between LH and FSH might be explained by different mechanisms of control; FSH secretion depends mainly on ovarian inhibition whereas LH secretion depends mainly on factors related to lactation. Folliculogenesis progressively resumes during lactation and follicles acquire the ability to respond to the weaning-associated stimuli and begin preovulatory growth. Hormones modified by lactation, such as prolactin, insulin, growth hormone and insulin-like growth factor I, may influence folliculogenesis directly at the ovarian level or via modifications of gonadotrophin secretions. In conclusion, the inhibition of the hypothalamo-pituitary-ovarian axis during lactation is mainly due to suckling-induced neuroendocrine reflexes. We hypothesize that the nutritional deficit becomes relatively more important during the third and fourth weeks pp.
Anestrus↗
Effect of ischemic preconditioning on interstitial purine metabolite and lactate accumulation during myocardial ischemia.
The purpose of this study was to determine the effect of ischemic preconditioning on the changes in interstitial fluid (ISF) purine metabolites and lactate during prolonged regional myocardial ischemia. The study consisted of two groups of anesthetized dogs: a control group (n = 13) that was exposed to 60 minutes of regional myocardial ischemia and a preconditioned group (n = 10). In the preconditioned group, regional myocardial ischemia was induced for two 5-minute episodes, each followed by 10 minutes of reperfusion. These preconditioning episodes were followed by 60 minutes of sustained regional ischemia. Cardiac ISF was sampled by microdialysis probes implanted in the left ventricular myocardium; dialysate levels served as indices of ISF concentrations. In the preconditioned group, dialysate concentrations of adenosine, inosine, hypoxanthine, total purines, and lactate increased during each of the 5-minute ischemia episodes, with further increases occurring during the first 5 minutes of reperfusion. However, the increases in dialysate purine metabolites during the first period of ischemia/reperfusion were greater than those that occurred during the second ischemia/reperfusion. In addition, preconditioning reduced the rate of ISF purine metabolite and lactate accumulation during the prolonged ischemia when compared with nonpreconditioned animals. These data suggest that preconditioning reduces the energy imbalance that occurs during subsequent myocardial ischemia and thereby diminishes the rate of net adenine nucleotide degradation and cellular production and release of purine metabolites and lactate. In addition, the increase in ISF adenosine seen during the preconditioning episode is consistent with the notion that preconditioning-induced cardioprotection is mediated in part by the action of adenosine at extracellular A1 adenosine receptors.
Adenosine↗
Effects of D-3-hydroxybutyrate and acetoacetate on lactate removal in isolated perfused livers from starved and fed rats.
We examined the influence of nutritional state on the role of the hepatic plasma membrane lactate transporter in determining overall hepatic lactate disposal. The effects of infusion of sodium D-3-hydroxybutyrate (DOHB) on lactate uptake were studied in perfused livers from fed or starved rats. In livers from starved rats, DOHB (15 to 20 mmol/L) inhibited lactate removal by approximately 45%. This effect was associated with a decrease in intracellular lactate concentration, with cell pH remaining unchanged. Inhibition was maximal when perfusate lactate was less than 1.6 mmol/L, and was undetectable at concentrations exceeding 2.5 mmol/L. A similar degree of inhibition was observed with infusion of acetoacetate. These observations add to the evidence that the inhibition of lactate removal by DOHB seen in livers from starved animals is mediated through an effect on the hepatocyte lactate transporter. At similar low levels of perfusate lactate, DOHB infusion produced a decrease in output of lactate from livers obtained from fed animals. When such livers were subjected to prolonged preperfusion, lactate removal, rather than output, was observed; in these livers DOHB stimulated lactate removal, an effect directionally opposite to that observed in livers from starved animals. These data confirm that hepatic lactate transport is a limiting factor for lactate utilization in intact livers from starved rats; in contrast, lactate utilization in livers from fed animals is limited at a step subsequent to plasma membrane transport, ie, possibly pyruvate transport into mitochondria.
3-Hydroxybutyric Acid↗
Calciotropic hormones during reproduction.
This review summarizes the reported effects of the menstrual cycle, pregnancy and lactation on serum concentration of the calciotropic hormones PTH and 1,25(OH)2D. A midcycle rise in PTH and 1,25(OH)2D has been observed, but in the majority of studies there was no change in PTH and 1,25(OH)2D concentrations throughout the menstrual cycle. Both total and free 1,25(OH)2D levels are increased during pregnancy. The renal 1,25(OH)2D production is stimulated, and there is some evidence of 1,25(OH)2D production by decidua/placenta and fetal kidney in vitro; the decidual/placental production should not be overestimated in vivo. The increased renal 1 alpha-hydroxylase activity is possibly mediated by estrogens and PTH, although the effect of pregnancy on PTH remains uncertain. Increased serum 1,25(OH)2D concentrations probably result in a rise of intestinal calcium absorption during pregnancy. There is a postdelivery drop in PTH and 1,25(OH)2D levels, but they are increased when lactation is prolonged, or in mothers nursing twins. The l alpha-hydroxylase activity during lactation may be stimulated by PTH, but also by prolactin.
Animals↗
Metabolic and contractile responses of fast- and slow-twitch rat skeletal muscles to ischemia.
Complete occlusion of blood flow to rat hind limb by tourniquet was used to study the effects of total ischemia for 1, 2, and 3 h on contractile function and metabolic behaviour of two muscles composed predominantly of either fast-twitch (extensor digitorum longus, EDL) or slow-twitch (soleus, SOL) fibres. Percent loss in twitch force (Pt) was greater (p < 0.05) in SOL than EDL during the first 45 min of ischemia. Following 1 h of ischemia, ATP concentration was lower (p < 0.05) than in the contralateral control (20.8 +/- 2.0 vs. 26.4 +/- 1.5 mmol/kg dry weight). Thereafter, the decline in ATP was greater, with approximately 95% depleted by 3 h of ischemia (1.46 +/- 0.46 mmol/kg dry weight). The effect of ischemia on ATP levels in the SOL was similar to ATP levels in the EDL, 1 h of ischemia also resulted in a large decrement in PCr, from 50.1 +/- 2.9 to 11.7 +/- 2.4 mmol/kg dry weight, and a large increase in lactate, from 25.0 +/- 3.0 to 114 +/- 10 mmol/kg dry weight. As ischemia was prolonged, only lactate was increased (p < 0.05) both at 2 h (171 +/- 12 mmol/kg dry weight) and 3 h (208 +/- 5.4 mmol/kg dry weight). Similar trends were found for SOL. By 3 h of ischemia, glycogen was depleted (p < 0.05) by 88% in EDL and 92% in SOL, respectively. These results support the hypothesis that both high energy phosphate transfer and anerobic glycolysis are of major importance in defending ATP hemostasis, particularly during the 1st h of ischemia, and that the resulting metabolic disturbances are responsible for the large fatigability observed. The mechanisms underlying the greater resistance to fatigue observed for the SOL compared with the EDL during the earlier period of ischemia remain uncertain.
Animals↗
Effect of dichloroacetate on oxidative removal of lactate in mice after supramaximal exercise.
1. The effect of dichloroacetate (DCA), which activates substrate oxidation on oxidative removal of lactate in mice after supramaximal exercise was investigated. 2. DCA significantly decreased the blood lactate concentration and increased the oxidative removal of lactate during prolonged exercise. 3. No significant differences were found in the removal of the blood lactate concentration, in oxidative removal of lactate after supramaximal exercise. 4. It is concluded that DCA administration which activates lactate oxidation during exercise does not activate lactate oxidation in mice after supramaximal exercise.
Animals↗
Lactate in working muscles after prolonged exercise.
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Adenine Nucleotides↗
Serial transcardiac lactate metabolism in post-reperfused stunned myocardium in evolving myocardial infarction.
To elucidate the relationship between lactate metabolism following reperfusion and restoration of left ventricular (LV) function, we assessed serial changes in transcardiac lactate metabolism following reperfusion therapy in 67 patients admitted to hospital within 6 h of the onset of acute anteroseptal myocardial infarction. Left ventriculograms taken about 30 min after reperfusion therapy revealed marked dyskinesis in the anteroapical region in all subjects. According to the regional ejection fraction (rEF), determined 4 weeks later as an index of LV function, patients were divided into 3 group: 1) Restored LV group: 28 patients with reperfusion and restored LV function (rEF greater than 30%); 2) Poor LV group: 26 patients with reperfusion but poor LV function (rEF less than 30%); 3) Failure group: 13 patients with failed reperfusion and occluded left anterior descending coronary artery. Although there was no difference in elapsed time and time to peak creatine phosphokinase (CPK) between the former 2 groups, the Restored LV group demonstrated lower peak CPK values, suggesting that these patients had less myocardial injury. Immediately after reperfusion, both groups showed transcardiac lactate production. In the Restored LV group, aerobic lactate metabolism was restored early after reperfusion (at 6 h), while in the Poor LV group prolonged anaerobic lactate metabolism was observed. These results suggest that an early restoration of aerobic metabolism might be a sign of stunned and viable myocardium, and a sustained lactate production might relate to a sustained process of myocardial injury.
Adult↗
Basal metabolic rate and energetics of reproduction in therian mammals.
Traditionally, the fact that reproduction in eutherian (= placental) mammals tends towards prolonged intrauterine development and short lactation has been interpreted as an evolutionary advance over the metatherian (= marsupial) short gestation and prolonged lactation. However, it has recently been postulated that marsupial reproduction involves low initial energy investment and may be advantageous by minimizing energy loss if conditions necessitate early termination. Moreover, because marsupials have basal metabolic rates (BMRs) 30% lower than those of most eutherians, it has been suggested that daily and total energy expenditures during reproduction may also be lower. We have now tested the predictions that low BMR is maintained during reproduction and that initial investment is lower in marsupials. Using indirect calorimetry, we have made the first longitudinal measurements of energy expenditure during reproduction for a marsupial and for two eutherian species with low BMRs. We find that initial investment is lowest in a eutherian and total energetic expenditures were greatest for the marsupial. We also find that, relative to BMR, all three species have increased mean maternal resting metabolic rates (RMRs) during both gestation and lactation; this is the first evidence that mammals with low BMRs can substantially elevate metabolism for prolonged periods during gestation and lactation.
Animals↗
Combined 1H and 31P nuclear magnetic resonance spectroscopic studies of bicuculline-induced seizures in vivo.
Using a 1.89-Tesla spectrometer, 1H and 31P nuclear magnetic resonance spectra were acquired from the brains of paralyzed rabbits ventilated with 30% oxygen in nitrous oxide. Intracellular pH and changes in lactate concentration in the cerebrum were monitored by nuclear magnetic resonance methods during and after bicuculline-induced seizures, together with the electroencephalogram, heart rate, and arterial blood pressure. During seizures lasting more than an hour, cerebral intracellular pH became acidic, the cerebral lactate level rose rapidly, and both changes persisted as long as 2 hours without signs of recovery. After less prolonged seizures, lactate elevations were no less persistent, despite nearly complete recovery of intracellular pH and the electroencephalogram.
Animals↗