Rates of incorporation of leucine (using L-[1-13C]leucine as a tracer) into myofibrillar and whole body proteins were determined in healthy old (> 60 yr old, n = 7) and young (< 30 yr old, n = 9) men and women who were fed small meals (4% of daily energy) every 30 min. There was no difference in whole body incorporation of leucine into proteins in the young (148 +/- 5 mumol.h-1.kg lean body mass-1, means +/- SE) and old groups (150 +/- 3 mumol.h-1.kg lean body mass-1). However, the fractional myofibrillar protein synthesis in the vastus lateralis muscle was 28% slower in the older group (0.063 +/- 0.004 vs. 0.088 +/- 0.003 %/h, P < 0.001). Extrapolation of these results to whole body myofibrillar synthesis (fractional rate x myofibrillar mass estimated by creatinine excretion) indicated that, in the older group, total myofibrillar synthesis was 43% slower (1.8 +/- 0.2 vs. 3.1 +/- 0.2 g/h, P < 0.01) and that their myofibrillar synthesis was a smaller portion of whole body protein synthesis (15 +/- 1 vs. 23 +/- 1%, P < 0.001). Compared with age-matched postabsorptive subjects, whole body protein synthesis was approximately 25% faster, and fractional myofibrillar synthesis was approximately 50% faster in these fed subjects, both young and old. We conclude that myofibrillar synthesis is slower in older subjects during both postabsorptive and postprandial conditions but that aging does not impair the stimulatory effect of feeding on protein synthesis.
The rate of synthesis of myofibrillar proteins is slower in muscle of healthy subjects over 60 yr old than it is in young adults. Previous research suggests that reduced activity of the GH/insulin-like growth factor-I system could be a determinant of this slowing of protein synthesis. To test the hypothesis that GH could rejuvenate the rate of myofibrillar protein synthesis, we studied healthy subjects over 60 yr old, after a single injection (0.03 mg/kg.sc) of recombinant human GH (n = 6 males/2 females) or placebo (n = 6 males/2 females), or after 3 months of either GH (0.03 mg/kg, sc, 3 x /week, n = 5 males) or placebo (n = 5 males) treatment. Myofibrillar protein synthesis and whole-body protein metabolism were evaluated with the tracer L-[1-13C]leucine. GH reduced whole-body leucine oxidation by 36% (P < 0.01) in the single injection study. There was no effect of GH on whole-body protein breakdown or synthesis, or on myofibrillar protein synthesis in the quadriceps, either acutely or after 3 months of treatment. GH treatment for 3 months increased lean body mass (3.3 +/- 0.7 kg, P < 0.01, as evaluated by 40K counting), muscle mass (3.3 +/- 1.1 kg, P < 0.02, as evaluated by urinary creatinine excretion), and thigh strength (14 +/- 5%, P < 0.05, as evaluated by isokinetic dynamometry). We conclude that GH can increase muscle mass and strength in healthy men over 60 yr old, but does not restore a youthful rate of myofibrillar protein synthesis.
Purpose: Many epidemiological studies have reported that sleep problems are frequent in children. A common sleep disturbance, sleep disordered breathing, is also known to vary by ethnicity, but little is known about other sleep problems that may be affected by racial background. The objective of this study was to assess the prevalence of sleep disturbances in community children and determine if racial differences exist. Methods: A detailed questionnaire related to sleep habits and sleep quality was mailed to parents of children enrolled in the community public school system. Children, aged 5 to 6 years of age, and who self-identified as Caucasian (C) or African American (AA) were eligible to participate. Results: 2000 questionnaires were eligible for analysis. Demographic data were as follows: 6 year olds, 1119 (56%); males, 1059 (53%); C, 1582 (79%). The average hours of nighttime sleep was 9.2 Ϯ 1.4 hours. The parents of C children reported more sleep hours than their AA counterparts (C, 9.4 Ϯ 1.3 hours vs. AA, 8.5 Ϯ 1.6 hours). Only 180 (9%) of parents reported no concerns with sleep issues, but of the remaining parents, racial differences did exist. More C parents reported that their children willingly went to bed (C, 60% vs. AA, 48%, p < .001) and were easy to arouse in the morning (C, 59% vs. AA, 52%, p = .007) than parents of AA children. Parents of AA children felt their children talked more during sleep (C, 12% vs. AA 29%, p < .001), had a higher frequency of sleepwalking (C, 1.9% vs. AA, 3.8%, p = .03), more nightmares (C, 1.9% vs. AA, 7.0%, p < .001), snored more frequently (C, 25% vs. AA, 45%, p < .001), and exhibited daytime somnolence more often (C, 8.9% vs. AA 13.2%, p < .001). Conclusion: Racial differences do exist in sleep habits and sleep quality. This study suggests AA children are more at risk for sleep disturbances than their C counterparts.
Increased flux through the hexosamine biosynthetic pathway (HBP) has been proposed as one mechanism by which hyperglycemia induces insulin resistance and complications associated with diabetes. Excess glucose entering the HBP is converted to UDP-GlcNAc, a sugar donor for the posttranslational glycosylation of Ser/Thr residues by O-linked N-acetylglucosamine monosaccharide (GlcNAc). This dynamic and reversible modification of cytosolic and nuclear proteins provides an alternative mechanism of protein regulation to phosphorylation. The purpose of this study was to assess whether increased O-GlcNAc modification of proteins precedes the development of glucose-induced insulin resistance in vivo.MethodsIn male Wistar rats, blood glucose was maintained at 10-12 mM by variable glucose infusion for 3 or 5 hours, after which blood glucose was returned to basal over 45 minutes by stepwise cessation of iv glucose. A 2-hour euglycemic hyperinsulinemic clamp (0.25 U/kg/hr) was then performed in these and saline-infused control rats. Insulin resistance was present in both muscle and liver after 5 but not after 3 hours of glucose infusion. Soluble protein, isolated from liver and gastrocnemius muscle of rats infused with saline or glucose for 3 or 5 hours, was separated by SDS-PAGE and transferred to nitrocellulose. Global protein O-GlcNAc modification was quantitated using an anti-O-GlcNAc antibody and normalized for protein loading using α-tubulin.ResultsPreliminary data suggest that in liver, but not in muscle, there is an increase in the global level of O-GlcNAc modification following 3 hours of glucose infusion. Analysis of the four most intense bands corresponding to O-GlcNAc modified proteins in the liver at 141 kDa, 130 kDa, 90 kDa, and 60 kDa showed an increase (range 20-500%) in the level of modification with glucose infusion. We found that the mean difference in protein modification between glucose- and saline-infused rats was borderline significant for the 141 kDa protein (p = .0751) and significant for the 90 kDa and 60 kDa proteins (p = .0479 and .0022, respectively) after adjusting for hour (3 vs 5) and accounting for correlation of repeated measures.ConclusionsIn an in vivo model of insulin resistance, a global increase in protein O-GlcNAc modification in liver precedes the development of insulin resistance.
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