The time course for the activation of glycogen phosphorylase (Phos) and pyruvate dehydrogenase (PDH) and their allosteric regulators was determined in human skeletal muscle during repeated bouts of maximal exercise. Six subjects completed three 30-s bouts of maximal isokinetic cycling separated by 4-min recovery periods. Muscle biopsies were taken at rest and at 6, 15, and 30 s of exercise during bouts 1 and 3. Phos was rapidly activated within the first 6 s of bout 1 from 12% at rest to 47% at 6 s. The activation of PDH increased from 14% at rest to 48% at 6 s and 95% at 15 s of bout 1. Phos reverted back to basal values at the end of the first bout, whereas PDH remained fully activated. In contrast, in the third bout, PDH was 42% at rest and was activated more rapidly and was nearly completely activated by 6 s, whereas Phos remained at basal levels (range 14-20%). Lactate accumulation was marked in the first bout and increased progressively from 2.7 to 76.1 mmol/kg dry wt with no further increase in bout 3. Glycogen utilization was also marked in the first bout and was negligible in bout 3. The rapid activation of Phos and slower activation of PDH in bout 1 was probably due to Ca(2+) release from the sarcoplasmic reticulum. Lactate accumulation appeared to be due to an imbalance of the relative activities of Phos and PDH. The increase in H(+) concentration may have served to reduce pyruvate production by inhibiting Phos transformation and may have simultaneously activated PDH in the third bout such that there was a better matching between pyruvate production and oxidation and minimal lactate accumulation. As each bout progressed and with successive bouts, there was a decreasing ability to stimulate substrate phosphorylation through phosphocreatine hydrolysis and glycolysis and a shift toward greater reliance on oxidative phosphorylation.
During the onset of exercise in hypoxia, the increased lactate accumulation is associated with a delayed activation of pyruvate dehydrogenase (PDH; Parolin ML, Spreit LL, Hultman E, Hollidge-Horvat MG, Jones NL, and Heigenhauser GJF. Am J Physiol Endocrinol Metab 278: E522-E534, 2000). The present study investigated whether activation of PDH with dichloroacetate (DCA) before exercise would reduce lactate accumulation during exercise in acute hypoxia by increasing oxidative phosphorylation. Six subjects cycled on two occasions for 15 min at 55% of their normoxic maximal oxygen uptake after a saline (control) or DCA infusion while breathing 11% O(2). Muscle biopsies of the vastus lateralis were taken at rest and after 1 and 15 min of exercise. DCA increased PDH activity at rest and at 1 min of exercise, resulting in increased acetyl-CoA concentration and acetylcarnitine concentration at rest and at 1 min. In the first minute of exercise, there was a trend toward a lower phosphocreatine (PCr) breakdown with DCA compared with control. Glycogenolysis was lower with DCA, resulting in reduced lactate concentration ([lactate]), despite similar phosphorylase a mole fractions and posttransformational regulators. During the subsequent 14 min of exercise, PDH activity was similar, whereas PCr breakdown and muscle [lactate] were reduced with DCA. Glycogenolysis was lower with DCA, despite similar mole fractions of phosphorylase a, and was due to reduced posttransformational regulators. The results from the present study support the hypothesis that lactate production is due in part to metabolic inertia and cannot solely be explained by an oxygen limitation, even under conditions of acute hypoxia.
To describe the characteristics of patients receiving belimumab, overall patterns of systemic lupus erythematosus (SLE) care, clinical outcomes, and changes in glucocorticoid dose following 6 months of therapy with belimumab, and healthcare resource utilization in belimumab users in Canadian clinical practice settings. Retrospective multicenter medical chart review study of adult patients with SLE who were prescribed belimumab as part of usual care and who received ≥8 infusions or 6 months of treatment. Primary endpoints included physician-determined overall clinical improvement from baseline, glucocorticoid use, and physician-determined SLE disease severity at Month 6. In total, 52 patients were included in the study. At belimumab initiation, 5.8/76.9/17.3% of patients had mild/moderate/severe SLE, respectively. Oral glucocorticoids were discontinued in 11.4% of patients and 59.1% received a lower dose at Month 6. At Month 6, 80.8/57.7/17.3% of patients had a physician-determined clinical improvement of ≥20/≥50/≥80%, respectively. Sixteen patients had a SLE Disease Activity Index-2K score at both baseline and Month 6, with a mean improvement of 2.6 ± 5.3 from 8.1 ± 3.2 at baseline. No formal disease assessment tool was utilized for 42.3% of study patients at baseline. This study provides the first real-world insights into belimumab use in Canada. It demonstrates significant reduction or discontinuation of glucocorticoid dose in 70.5% of patients and clinically significant improvement following 6 months’ belimumab therapy. The high number of patients with no formal disease activity assessments highlights a key care gap in SLE treatment in the real-world setting.
These are considered the first guidelines using the GRADE method for the monitoring of SLE. Existing evidence is largely of low to moderate quality, resulting in more conditional than strong recommendations. Additional rigorous studies and special attention to pediatric SLE populations and patient preferences are needed.
Ultrasound of the hands and/or feet significantly influenced the rheumatologists' diagnostic confidence in specific clinical findings and management plans.
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