Metabolic adaptations in skeletal muscle overexpressing GLUT4: effects on muscle and physical activity.

To understand the long-term metabolic and functional consequences of increased GLUT4 content, intracellular substrate utilization was investigated in isolated muscles of transgenic mice overexpressing GLUT4 selectively in fast-twitch skeletal muscles. Rates of glycolysis, glycogen synthesis, glucose oxidation, and free fatty acid (FFA) oxidation as well as glycogen content were assessed in isolated EDL (fast-twitch) and soleus (slow-twitch) muscles from female and male MLC-GLUT4 transgenic and control mice. In male MLC-GLUT4 EDL, increased glucose influx predominantly led to increased glycolysis. In contrast, in female MLC-GLUT4 EDL increased glycogen synthesis was observed. In both sexes, GLUT4 overexpression resulted in decreased exogenous FFA oxidation rates. The decreased rate of FFA oxidation in male MLC-GLUT4 EDL was associated with increased lipid content in liver, but not in muscle or at the whole body level. To determine how changes in substrate metabolism and insulin action may influence energy balance in an environment that encouraged physical activity, we measured voluntary training activity, body weight, and food consumption of MLC-GLUT4 and control mice in cages equipped with training wheels. We observed a small decrease in body weight of MLC-GLUT4 mice that was paradoxically accompanied by a 45% increase in food consumption. The results were explained by a marked fourfold increase in voluntary wheel exercise. The changes in substrate metabolism and physical activity in MLC-GLUT4 mice were not associated with dramatic changes in skeletal muscle morphology. Collectively, results of this study demonstrate the feasibility of altering muscle substrate utilization by overexpression of GLUT4. The results also suggest that as a potential treatment for type II diabetes mellitus, increased skeletal muscle GLUT4 expression may provide benefits in addition to improvement of insulin action.

Age, fatigue, and excitation-contraction coupling in masseter muscles of rats.

The purpose of this study was to determine if masseter muscle endurance changes with increasing age and, if so, to examine mechanisms of fatigue. Characteristics of fatigue were measured under isometric conditions using high-frequency stimulation of anterior deep masseter (ADM) muscles of male Fischer 344 rats, 5 to 24 months old, and fed a hard (HD) or a soft (SD) diet. Potentiating effects of caffeine on ADM muscle performance in vitro were also examined. Fatigability increased by 48% with age in muscles of HD rats. Muscles of SD rats were highly fatigable at all ages. Increased HD fatigability was associated with significantly decreased concentrations of Na+/K+-adenosine triphosphatase (22%) and decreased responsiveness to caffeine postfatigue (29%). The pH levels decreased similarly in fatigued muscles of all groups. We conclude that the age-related increase in fatigability is associated with alterations in excitation-contraction coupling mechanisms. However, differences between SD and HD on ADM muscles represent possible fiber-type transitions.

Lipoprotein (a) and the risk of ischemic stroke in young women.

BACKGROUND AND PURPOSE: lipoprotein (a) (lp (a)) is a lipid-containing particle similar to LDL which has been found in atherosclerotic plaque. The role of lp (a) in ischemic stroke remains controversial, but some studies suggest lp (a) is particularly important as a risk factor for stroke in young adults. We investigated the role of lp (a) as a risk factor for stroke in young women enrolled in the Stroke Prevention in Young Women Study. METHODS: subjects were participants in a population-based, case-control study of risk factors for ischemic stroke in young women. Cases were derived from surveillance of 59 regional hospitals in the central Maryland, Washington DC, Pennsylvania and Delaware area. Lp (a) was measured in 110 cases and 216 age-matched controls. Demographics, risk factors, and stroke subtype were determined by interview and review of medical records. RESULTS: lp (a) values were higher in blacks than whites, but within racial groups, the distribution of lp (a) values was similar between cases and controls. After adjustment for age, race, hypertension, diabetes, cigarette smoking, coronary artery disease, total cholesterol and HDL cholesterol, the odds ratio for an association of lp (a) and stroke was 1.36 (95% CI 0.80-2.29). There was no dose-response relationship between lp (a) quintile and stroke risk. Among stroke subtypes, only lacunar stroke patients had significantly elevated lp (a) values compared to controls. CONCLUSIONS: we found no association of lp (a) with stroke in a population of young women with ischemic stroke. Small numbers of patients limit conclusions regarding risk in ischemic stroke subtypes, but we could not confirm previous suggestions of an association of lp (a) with atherosclerotic stroke in young adults.

Cognitive functioning after subthalamic nucleotomy for refractory Parkinson's disease.

OBJECTIVE: To evaluate whether subthalamic nucleotomy produces adverse cognitive effects in patients with Parkinson's disease. METHOD: Twelve patients with Parkinson's disease underwent stereotactic surgery to the subthalamic nucleus. Presurgical and postsurgical neuropsychological assessment of attention, memory, executive function, language, and verbal intellect were undertaken with a battery of tests designed to minimise potential contamination of cognitive effects by motor symptoms. RESULTS: There was no statistically significant difference in the cognitive tests results after operation for the group as a whole. Reliable change indexes were generated for the cognitive tests. Reliable change postoperatively was found on specific tests of verbal memory, attention, and planning. Left sided operations were associated with greater incidence of deterioration postsurgery. CONCLUSIONS: Preliminary data on the first reported cognitive changes after subthalamic nucleotomy suggested few adverse cognitive effects of the surgery although discrete neuropsychological changes were seen in some patients. These effects were consistent with current theories on the cognitive functions of the basal ganglia.

Elevated tissue plasminogen activator antigen and stroke risk: The Stroke Prevention In Young Women Study.

BACKGROUND AND PURPOSE: Abnormalities in endogenous fibrinolysis are associated with an increased risk for stroke in men and older adults. We tested the hypothesis that elevated plasma tissue plasminogen activator (tPA) antigen, a marker for impaired endogenous fibrinolysis, is an independent risk factor for stroke in young women. METHODS: Subjects were 59 nondiabetic females ages 15 to 44 years with cerebral infarction from the Baltimore-Washington area and 97 control subjects frequency-matched for age who were recruited by random-digit dialing from the same geographic area. A history of cerebrovascular disease risk factors was obtained by face-to-face interview. Plasma tPA antigen was measured by enzyme-linked immunosorbent assay. RESULTS: Mean plasma tPA antigen levels were significantly higher in stroke patients than control subjects (4. 80+/-4.18 versus 3.23+/-3.67 ng/mL; P=0.015). After adjustment for age, hypertension, cigarette smoking, body mass index, and ischemic heart disease, there was a dose-response association between tPA antigen and stroke with a 3.9-fold odds ratio of stroke (95% CI, 1.2 to 12.4; P=0.03) for the upper quartile (>4.9 ng/mL) of tPA antigen compared with the lowest quartile. The dose-response relationship between tPA antigen and stroke was equally present in white and nonwhite women, and further adjustment for total and HDL cholesterol levels only modestly attenuated this association. CONCLUSIONS: This population-based case-control study shows that elevated plasma tPA antigen level is independently associated with an increased risk for ischemic stroke in nondiabetic females 15 to 44 years of age. These findings support the hypothesis that impaired endogenous fibrinolysis is an important risk factor for stroke in young women.

Distribution and correlates of elevated total homocyst(e)ine: the Stroke Prevention in Young Women Study.

PURPOSE: To determine the distribution and correlates of elevated total homocyst(e)ine (tHcy) concentration in a population of premenopausal black and white women. METHODS: Data from the Stroke Prevention in Young Women Study (N = 304), a population-based study of risk factors for stroke in women aged 15-44 years of age, were used to determine the distribution and correlates of elevated tHcy in black (N = 103) and white women (N = 201). RESULTS: The mean tHcy level for the population was 6.58 micromol/L (range 2.89-26.5 micromol/L). Mean tHcy levels increased with age, cholesterol level, alcohol intake, and number of cigarettes smoked (all: p < 0.05). There were no race differences (mean tHcy 6.72 micromol/L among blacks and 6.51 micromol/L among whites; p = 0.4346). Regular use of multivitamins and increasing education was associated with significant reductions in tHcy concentration. Approximately 13% of the sample had elevated tHcy levels, defined as a tHcy concentration > or = 10.0 micromol/L. Multivariate-adjusted correlates of elevated tHcy included education > 12 vs. < or = 12 (odds ratio [OR] = 0.4, 95% confidence interval [CI] = 0.2-0.8); smoking > or = 20 cigarettes/day vs. nonsmokers (OR = 2.8, 95% CI = 1.1-7.3); and the regular use of multivitamins (OR = 0.4, 95% CI = 0.2-0.9). CONCLUSIONS: These results suggest that a substantial proportion of healthy young premenopausal women have tHcy levels that increase their risk for vascular disease. A number of potentially modifiable behavioral and environmental factors appear to be significantly related to elevated tHcy levels in young women.

Effects of fiber type on ischemia-reperfusion injury in mouse skeletal muscle.

Tourniquets frequently used during surgery involve tissue ischemia followed by postoperative reperfusion. However, little information is available on the functional consequences of this procedure in skeletal muscle. The goal of this study was to use skeletal muscles of C57BL/6 adult male mice to assess functional, structural, and biochemical characteristics after hindlimb vessel occlusion. Experimental manipulation involved application of a tourniquet to the hindlimb for a 3-hour period (n = 65). Muscles were then excised after various periods of reperfusion. Soleus and extensor digitorum longus muscles were chosen as representative of slow oxidative and fast glycolytic muscle fiber types, respectively. The most striking functional change found after ischemia-reperfusion injury was markedly improved endurance of extensor digitorum longus muscles. These fast-twitch glycolytic muscle fibers became much more resistant to fatigue during recovery from ischemia-reperfusion injury. There was a progressive increase in force generation in both muscles during recovery; however, soleus muscles recovered function more quickly after ischemia-reperfusion than extensor digitorum longus muscles. Also, extensor digitorum longus muscles recovered mass more slowly than soleus muscles at 7 and 14 days after ischemia. Structurally, extensor digitorum longus muscles had more severely damaged mitochondria, sarcoplasmic reticulum, and myofibrils. Surprisingly, no differences in oxidative enzyme activity (citrate synthase) and oxidative damage (in protein and lipids) were found after ischemia-reperfusion. The results indicate that muscle fiber type has a significant impact on the nature of ischemia-reperfusion injury in skeletal muscle. Thus, muscle fiber composition would be expected to affect recovery from the clinical use of tourniquets and other ischemic procedures. Furthermore, the results suggest that damage to structures involved in energy transduction and excitation-contraction coupling may play a role in the effects.

Thermolabile methylenetetrahydrofolate reductase polymorphism (C677T) and total homocysteine concentration among African-American and white women.

A polymorphism associated with a thermolabile variant (C677T) of the enzyme methylenetetrahydrofolate reductase has been associated with both elevated total homocysteine (tHcy) levels and risk for cardiovascular disease. Data from the Stroke Prevention in Young Women Study were used to determine the prevalence of the C677T genotype and to assess whether environmental factors modified the association between genotype and tHcy concentration. The C677T genotype prevalence was 80% -/-, 20% +/-, and 0% +/+ among 46 African-American women; and 39% -/-, 53% +/-, and 8% +/+ among 77 white women (P < 0.01). There was a trend toward higher tHcy levels in African-American women with the +/- genotype when compared with the -/- genotype (6.9 mumol/L vs 5.3 mumol/L respectively, p = 0.10); no association was found among the white women (6.0 mumol/L, -/-; 4.5 mumol/L, +/-; and 6.2 mumol/L, +/+; p = 0.67). Among African American women, those who smoked and were +/- genotype had the highest tHcy levels (8.0 mumol/L); while among white women, those who smoked and were -/- had the highest tHcy levels (8.1 mumol/L). Despite being hampered by a limited sample size, the thermolabile allele is significantly less common among African-American than white women. The association between genotype and tHcy concentration is influenced by smoking and multivitamin use.

Clostridium difficile infection is a risk factor for bacteremia due to vancomycin-resistant enterococci (VRE) in VRE-colonized patients with acute leukemia.

A cohort study was conducted in a cancer center to identify risk factors for bacteremia with vancomycin-resistant enterococci (VRE) in neutropenic cancer patients colonized with VRE. There were 10 patients with VRE bacteremia among 56 colonized with VRE, of whose charts 51 were available for review. One hundred percent of patients with VRE bacteremia (10 of 10) vs. 56% of patients without VRE bacteremia (23 of 41) had acute leukemia (P = .01, Fisher's exact test). Four of the 10 patients with VRE bacteremia had a positive Clostridium difficile toxin assay within 6 days of their first positive VRE blood culture. Both C. difficile infection and antimicrobial (vancomycin and ciprofloxacin) use during VRE colonization were significant risk factors for VRE bacteremia in univariate analysis. When a Cox proportional hazards model was used to account for differences in follow-up time, C. difficile infection was the only statistically significant risk factor (risk ratio, 8.2; P = .007) for VRE bacteremia in VRE-colonized patients with acute leukemia.

Physical activity as a factor in the action of dietary restriction on aging: effects in Fischer 344 rats.

Dietary restriction (DR) slows the rate of aging in laboratory rodents but the mechanism of action is unknown. DR is known to induce beneficial effects in a variety of tissues and organ systems. DR also maintains high levels of physical activity over the life span. We tested the hypothesis that lifelong physical activity is an important component of the anti-aging action of DR. Male specific pathogen-free Fischer 344 rats were divided into 4 groups at 6 weeks of age: A: fed old libitum; AE: fed ad libitum and in cages with running wheels; B: fed 60% ad libitum; BE: fed 60% ad libitum and in cages with running wheels. Running activity and spontaneous cage activity were measured over 24 hours and over the life span. Metabolic rate was measured indirectly by analysis of air entering and leaving cages. AE rats exhibited low levels of running activity and ran very little beyond 6 months of age. In contrast, BE rats sustained high running levels even after all A and AE rats had died. High levels of wheel running did not decrease spontaneous cage activity. Median life span (50% survival) was in the order A = AE < B < BE. Ten percent survival was in the order A = AE < B = BE. BE rats had greatest median life span and also highest specific metabolic rate. Exercise and DR altered pathology: At death BE rats had a high incidence of cardiomyopathy, whereas A and AE rats had high incidence of chronic nephropathy and pituitary tumors. The data indicate that increased physical activity is probably not an important factor in the action of DR on aging.

Exercise and diet modulate cardiac lipid peroxidation and antioxidant defenses.

Free radical metabolism can be altered by several interventions, including dietary restriction (DR) and exercise. Most of the previous work has focused on the liver and skeletal muscle. The following experiments were performed to determine whether long-term DR and chronic exercise affect free radical metabolism and change the status of the antioxidant defenses of the heart. Rats were subjected to DR and/or endurance exercise for 18.5 months and were sacrificed along with their ad lib fed and sedentary controls. Both DR and exercise decreased the malondialdehyde content of cardiac mitochondria, indicating a decrease in lipid peroxidation damage. The antioxidant enzymes in the cytosol, superoxide dismutase, selenium dependent glutathione peroxidase, and glutathione S-transferase were all increased by DR. Catalase activity was unaffected by DR but was increased by exercise. The following results demonstrate that long-term DR and exercise modulate the extent of free radical damage in the heart and enhance the antioxidant defense system.

Beneficial versus adverse effects of long-term use of clenbuterol in mdx mice.

Long-term administration of the beta 2-adrenergic agonist clenbuterol in mdx mice was used to test the hypothesis that increasing contractile protein content in skeletal muscle will decrease the progression of muscular dystrophy. C57BL/10SNJ (control) and dystrophic (mdx) mice were given clenbuterol (1.0-1.5 mg/kg body weight/day) in the drinking water. Ventilatory function and morphological and functional characteristics of soleus (SOL) and diaphragm (DIA) muscles were evaluated. Clenbuterol administration was associated with increased SOL muscle weight, and SOL muscle weight to body weight ratio in control and mdx mice at both ages. There was a 22% increase in myosin concentration of mdx DIA at 1 year of age, correlating well with increased normalized active tension in mdx DIA at this age. Also, absolute tetanic tension increased in control and mdx SOL with clenbuterol at both ages. Ventilatory function was significantly impaired in mdx mice at both ages and clenbuterol administration did not alleviate this. Clenbuterol treatment was associated with a 30-40% increase in fatigability in DIA and SOL muscles of control and mdx mice at both ages. Furthermore, 1-year-old mdx mice receiving clenbuterol exhibited deformities in hindlimbs and spine. These results suggest that long-term clenbuterol treatment has a positive effect on muscle growth and force generation, but has adverse side effects such as increased muscle fatigability and development of deformities.

Changes in alcohol, cigarette, and recreational drug use during pregnancy: implications for intervention.

From the Baltimore-Washington Infant Study, a regional epidemiologic study of congenital cardiovascular malformations, 1,336 mothers of infants selected as controls (a representative sample of the area birth cohort enrolled between April 1, 1981 and September 1, 1984) were studied with respect to alcohol, cigarette, and recreational drug use prior to and during pregnancy. Nearly half of the 1,336 women abstained from any substance use during pregnancy. Of the remainder, half restricted substance use to only alcohol or cigarettes. Only cigarette smokers showed a majority (68.5%) of women failing to successfully quit during pregnancy. Cigarette and recreational drug use during pregnancy was associated with lower socioeconomic status, while alcohol use was associated with higher social status. Cessation of cigarette and recreational drug use was more common among professionals and the college-educated, but these same characteristics, along with higher income, were associated with failure to quit drinking. Younger women were less likely to use alcohol and cigarettes and more likely to successfully quit these habits once adopted. Use of alcohol and tobacco was greater among whites, and recreational drug use was greater among black women, but race was not associated with quitting use of any substance. Length of time trying to become pregnant and the mother's perceived health were not found to be associated with substance use or quitting. This sociodemographic profile suggests subgroups which must be targeted for intervention by the prenatal care provider, as well as intervention strategies.

Cardiac and noncardiac malformations: observations in a population-based study.

A regional case-control study of congenital cardiovascular malformations (CCVMs) searches for all live-born infants in the community in whom the cardiac diagnosis has been confirmed by echocardiography, cardiac catheterization, surgery, or autopsy. Their families are studied in comparison to those of a representative sample of resident live-born infants. Detailed descriptions of noncardiac abnormalities are obtained from physician reports and maternal interviews expanded by medical record and death certificate data. Among 1,494 cases and 1,572 controls, chromosomal abnormalities, syndromes, heritable disorders, and suspect syndromes occurred with an overwhelming excess in cases (chromosomes, P less than 10(-4); syndromes/heritable disorders, P less than .005). Abnormalities affecting chromosomes 13, 18, and 21 constituted 93% of the cytogenetic defects. Syndromes and heritable disorders were of 39 types. Nonsyndromic abnormalities were three times more frequent in cases than in controls (P less than .005). Case excesses occurred for central nervous system malformations, eye disorders, major abdominal wall defects, and abnormalities of the alimentary and urinary tracts. Severe anomalies frequent among cases were those which also occur in certain recognized syndromes, and it is suggested that paired combinations of cardiac and other midline anomalies may represent "formes frustes" of syndromes with similar though variable phenotypic expressions. Cleft lip and palate, inguinal hernia, and lower limb anomalies occurred with equal frequency, suggesting their association with CCVMs by chance alone.

Congenital heart disease: prevalence at livebirth. The Baltimore-Washington Infant Study.

The Baltimore-Washington Infant Study is a regional epidemiologic study of congenital heart disease. Among Infants born in the study area in 1981 and 1982, 664 had a diagnosis of congenital heart disease confirmed in the first year of life by echocardiography, cardiac catheterization, cardiac surgery, or autopsy. The prevalence rate was 3.7/1,000 livebirths for all cases and 2.4/1,000 livebirths for cases confirmed by invasive methods only. Diagnosis-specific prevalence rates of congenital heart disease are compared with those of eight previous case series. Changing diagnostic categorizations in the time span covered and methodological differences resulted in great variation of the data. However, the data of the New England Infant Cardiac Program which used the same case discovery methods showed similar occurrences of major morphologic abnormalities, suggesting that these are stable basic estimates in the eastern United States. For all case series, the rate of confirmed congenital heart disease was approximately 4/1,000 livebirths over the 40-year time span.