Effect of prolonged exercise and pre-exercise dietary manipulation on hepatic triglycerides in trained men.

The purpose of this study was to examine the effect of exercise and pre-exercise dietary manipulation on hepatic triglyceride concentration (HTGC). HTGC was measured by proton magnetic resonance spectroscopy ((1)H-MRS) before and after 90 min of moderate intensity cycling in six endurance trained males following 67 h of mixed diet (M) and an isocaloric minimal carbohydrate (2%) high fat (83%) diet (HF). Diets were administered by balanced crossover design. Whole-body fat oxidation, plasma-free fatty acid (FFA), glycerol and triglyceride concentrations were significantly elevated during exercise in HF versus M (P < 0.05 for all). There was no significant treatment × time interaction for HTGC (P = 0.368). However, there was a significant net increase in HTGC (time effect) during the combined 6 h exercise and post-exercise period (P = 0.037). In conclusion, we observed no measurable net change in the hepatic triglyceride pool across a period involving a prolonged exercise bout. Furthermore, manipulation of pre-exercise dietary intake did not influence the interaction between the hepatic triglyceride concentration and exercise in lean trained men. This supports the contention that hepatic triglycerides do not meaningfully contribute to the high rate of fat oxidation observed during acute exercise, or the enhancement of this with regular exercise training and/or pre-exercise dietary manipulation.

Skeletal muscle strength and endurance are maintained during moderate dehydration.

This study investigated the effects of moderate dehydration (~2.5% body weight) on muscle strength and endurance using percutaneous electrical stimulation to quantify central and peripheral fatigue, and isolate the combined effects of exercise-heat stress and dehydration, vs. the effect of dehydration alone. Force production and voluntary activation were calculated in 10 males during 1 brief and 15 repeated maximal voluntary isometric contractions performed prior to (control) walking in the heat (35°C), immediately following exercise, and the next morning (dehydration). The protocol was also performed in a euhydrated state. During the brief contractions, force production and voluntary activation were maintained in all trials. In contrast, force production decreased throughout the repeated contractions, regardless of hydration status (P<0.001). The decline in force was greater immediately following exercise-heat stress dehydration compared with control and euhydration (P<0.001). When dehydration was isolated from acute post-exercise dehydration, force production was maintained similarly to control and euhydration. Despite the progressive decline in force production and the increased fatigability observed during the repeated contractions, voluntary activation remained elevated throughout each muscle function test. Therefore, moderate dehydration, isolated from acute exercise-heat stress, does not appear to influence strength during a single contraction or enhance fatigability.

Heat exposure does not alter eccentric exercise-induced increases in mitochondrial calcium and respiratory dysfunction.

Eccentric exercise can lead to muscle damage including dramatic changes to mitochondrial calcium content (MCC) and impaired respiratory function. Heat acclimation can create a cross-tolerance to a number of stresses including eccentric exercise but little is known about any protection to mitochondria. We hypothesised that intermittent heat exposure will lead to improved control of MCC and to preserved mitochondrial function following eccentric exercise. Sprague-Dawley rats were exposed to 3 weeks of intermittent heat exposure (36°C, 40% relative humidity, 6 h/day, 5 days a week) or kept in cool conditions (20°C). Animals were then assigned to a control or exercise group (-14°C decline treadmill exercise for 90 min). MCC, mitochondrial respiration and mitochondrial permeability transition pore opening (mPTP) were measured in mitochondria isolated from the red quadriceps in animals killed immediately, 2 h and 48 h post-exercise. Results showed that heat exposure was associated with lower plasma creatine kinase levels (p < 0.05) post-exercise suggesting lower levels of muscle damage. There was a significant (~500%) rise in MCC (p < 0.001) and a reduction in mitochondrial respiratory control ratio (p < 0.001) 48 h post-exercise. mPTP displayed increased (p < 0.05) sensitivity to calcium immediately and 48 h post-exercise. Thus, decline running led to significant impairment of mitochondria respiration and calcium loading which was more pronounced 48 h post-exercise compared with earlier time points. MCC levels and mitochondrial function were not altered by heat exposure. In conclusion, intermittent heat exposure does not appear to provide protection against mitochondrial dysfunction resulting from eccentric exercise.

Frame-shift deletions in patients with Duchenne and Becker muscular dystrophy.

Duchenne muscular dystrophy (DMD) and its less severe form Becker muscular dystrophy (BMD) are allelic disorders. It has been suggested that in the mutations involving BMD, the translational reading frame of messenger RNA is maintained and a smaller, though partially functional, protein is produced. In order to test this, the exon-intron boundaries of the first ten exons of the DMD gene were determined, and 29 patients were analyzed. In a number of BMD patients (mild and severe BMD), the reading frame of messenger RNA was not maintained. On the basis of these findings, a model for reinitiation from an internal start codon is suggested.

Biochemical and genetic studies in cystinuria: observations on double heterozygotes of genotype I-II.

10 families with cystinuria were investigated by measuring: (a) quantitative 24 hr urinary excretion of amino acids by column chromatography; (b) endogenous renal clearances of amino acids and creatinine; (c) intestinal uptake of (34)C-labeled L-cystine, L-lysine, and L-arginine using jejunal mucosal biopsies; (d) oral cystine loading tests. All four of these were studied in the probands and the first two in a large number of the family members.49 members of 8 families were found to have a regular genetic pattern as described previously by Harris, Rosenberg, and their coworkers. Clinical or biochemical differences between the homozygotes type I (recessive cystinuria) and homozygotes type II (incompletely recessive cystinuria) have not been found. Both types excreted similarly excessive amounts of cystine, lysine, arginine, and ornithine, and had high endogenous renal clearances for these four amino acids. Some homozygotes of both types had a cystine clearance higher than the glomerular filtration rate. Jejunal mucosa from both types of homozygotes exhibited near complete inability to concentrate cystine and lysine in vitro. This was also documented in vivo with oral cystine loads. The heterozygotes type I were phenotypically normal with respect to the above four measurements. The heterozygotes type II showed moderate but definite abnormalities in their urinary excretion and their renal clearances of dibasic amino acids. Of the four amino acids concerned, cystine was the most reliable marker to differentiate between the heterozygotes type II and the homozygous normals. In this study, type III cystinuria, as described by Rosenberg, was not encountered. In two additional families, double heterozygotes of genotype I/II were found. The disease affecting these is clinically and biochemically less severe than that affecting homozygotes of either type I or type II. With respect to the four parameters used in this study, the double heterozygotes type I/II have results which are intermediate between those of the homozygotes type I and II and those of the heterozygotes type II.

Chronic hypertension and altered baroreflex responses in transgenic mice containing the human renin and human angiotensinogen genes.

We have generated a transgenic model consisting of both the human renin and human angiotensinogen genes to study further the role played by the renin-angiotensin system in regulating arterial pressure. Transgenic mice containing either gene alone were normotensive, whereas mice containing both genes were chronically hypertensive. Plasma renin activity and plasma angiotensin II levels were both markedly elevated in the double transgenic mice compared with either single transgenic or nontransgenic controls. The elevation in blood pressure caused by the human transgenes was independent of the genotype at the endogenous renin locus and was equal in mice homozygous for the Ren-1c allele or in mice containing one copy each of Ren-1c, Ren-1d, or Ren-2. Chronic overproduction of angiotensin II in the double transgenic mice resulted in a resetting of the baroreflex control of heart rate to a higher pressure without significantly changing the gain or sensitivity of the reflex. Moreover, this change was not due to the effects of elevated pressure itself since angiotensin-converting enzyme inhibition had minimal effects on the baroreflex in spontaneously hypertensive BPH-2 control mice, which exhibit non-renin-dependent hypertension. This double transgenic model should provide an excellent tool for further studies on the mechanisms of hypertension initiated by the renin-angiotensin system.

Moderate- and high-intensity exhaustive exercise in the heat induce a similar increase in monocyte Hsp72.

This study examined the relationship between exhaustive exercise in the heat at moderate and high intensities on the intracellular heat shock protein 72 (iHsp72) response. Twelve male subjects cycled to exhaustion at 60 and 75% of maximal oxygen uptake in hot conditions (40 °C, 50% RH). iHsp72 concentration was measured in monocytes before, at exhaustion and 24 h after exercise. Rectal temperature, heart rate and oxygen uptake were recorded during exercise. Volitional exhaustion occurred at 58.9 ± 12.1 and 27.3 ± 9.5 min (P < 0.001) and a rectal temperature of 39.8 ± 0.4 and 39.2 ± 0.6 °C (P = 0.002), respectively, for 60 and 75 %. The area under the curve above a rectal temperature of 38.5 °C was greater at 60 % (17.5 ± 6.6 °C min) than 75 % (3.4 ± 4.8 °C min; P < 0.001), whereas the rate of increase in rectal temperature was greater at 75 % (5.1 ± 1.7 vs. 2.2 ± 1.4 °C h(-1); P < 0.001). iHsp72 concentration increased similarly at exhaustion relative to pre-exercise (P = 0.044) and then increased further at 24 h (P < 0.001). Multiple regression analysis revealed no predictor variables associated with iHsp72 expression; however, a correlation was observed between exercise intensities for the increase in iHsp expression at exhaustion and 24 h (P < 0.05). These results suggest that iHsp72 expression increased in relation to the level of hyperthermia attained and sustained at 60 % and the higher metabolic rate and greater rate of increase in core temperature at 75 %, with the further increase in iHsp72 concentration 24 h after exercise reinforcing its role as a chaperone and cytoprotective agent.

Regulation of human renin mRNA expression and protein release in transgenic mice.

The renin-angiotensin system plays a major role in the regulation of blood pressure and electrolyte homeostasis in mammals. In this study, we subjected transgenic mice containing a human renin genomic construct to a variety of pharmacological and physiological manipulations to test whether expression of the human renin gene and release of active human renin in appropriately regulated in this model. These manipulations were designed to test major regulators of renin release, including angiotensin II, the macula densa, renal perfusion pressure, and beta-adrenergic receptors. We used human plasma renin concentration and human renal renin mRNA levels to document the response of the transgene to these stimuli. Human plasma renin concentration increased in response to both angiotensin-converting enzyme inhibition with captopril and isoproterenol and decreased after a high salt diet. A low salt or sodium-deficient diet did not stimulate renin release. Human renin mRNA levels in kidney increased after captopril but were unchanged in the other experimental groups. We also measured the levels of human renin mRNA in double transgenic mice containing the same human renin gene in addition to the human angiotensinogen gene. These mice are chronically hypertensive and have increased circulating levels of angiotensin II. Human renin mRNA levels in the kidney were paradoxically elevated compared with their single transgenic normotensive counterparts. These transgenic mice provide a model for examination of human renin regulation and may help elucidate the molecular mechanisms that regulate the gene in response to physiological cues.

Complex segregation analysis and computer-assisted genetic risk assessment for Duchenne muscular dystrophy.

Two hundred forty-four Toronto pedigrees of Duchenne muscular dystrophy patients have been partitioned into nuclear families with pointers for complex segregation analysis under a mixed model. The model takes into account the major X-linked locus and a multifactorial transmissible component for creatine kinase activity in females. The incidence in the province of Ontario is estimated to be 292 per million male births. The proportion of sporadic cases is 1/3, demonstrating equal mutation rates in males and females. A multifactorial component (H = 0.379) contributes to family resemblance for creatine kinase measurements. Examples are presented of the application of a computer program, COUNSEL, to derive genetic risks for genetic counseling with consideration of the multifactorial component.

Duchenne muscular dystrophy carrier detection using logistic discrimination: serum creatine kinase, hemopexin, pyruvate kinase, and lactate dehydrogenase in combination.

In the absence of an unambiguous test for identifying Duchenne muscular dystrophy (DMD) heterozygotes, methods are needed for combination of the results of individually equivocal tests as effectively and rationally as possible. Tw used logistic discrimination to assess the effectiveness of measurements of serum creatine kinase, hemopexin, pyruvate kinase, and lactate dehydrogenase alone and in various combinations in identifying DMD carriers. We analyzed 127 serum samples from 63 normal female controls (20-40 years old) and 67 from 38 obligate DMD carriers. The best two tests to use in combination were creatine kinase and hemopexin, and these two, with lactate dehydrogenase, were the best three. t the 95% level (with 5% of controls misclassified), 54% of the carriers were identified by CK alone, whereas 88% were identified by means of the four tests. Although a small proportion of known carriers still cannot be identified, application of the four tests to a group of 45 possible carrier mothers of isolated cases of DMD resolves the population into fairly discrete "normal" and "abnormal" subgroups. Thus, if bias of selection can be eliminated, application of logistic discrimination may permit a direct estimate of the proportion of mothers of affected boys who are homozygous normal.

Duchenne muscular dystrophy carrier detection using logistic discrimination: serum creatine kinase and hemopexin in combination.

Creatine kinase (CK) activity and hemopexin concentration were measured in 208 serum samples from 104 normal females and 22 obligate carriers of Duchenne muscular dystrophy (DMD) 20-40 years old. Logistic discrimination was used to assess the effectiveness of the parameters alone or in combination in identifying DMD carriers. In this approach, a serum sample with particular CK, hemopexin, or a combination of CK and hemopexin values is given a probability that if drawn at random from a defined mixture of controls and carriers, it comes from a carrier. The carrier probability based on the biochemical tests can be directly combined with the carrier probability determined from a woman's pedigree to yield a final posterior probability that she is a carrier. When CK and hemopexin were considered individually, 65 and 27% of the carriers, respectively, could be distinguished from 95% of the controls. When the two tests were used in combination, 82% of the carriers could be distinguished from 95% of the controls. When the two-test method was applied to 93 possible carriers, 35 women were classified as carriers, whereas only 29 were identified using CK alone. This method can be extended to include other variables in order to further improve the identification of DMD carriers. It can also be applied to carrier detection in other genetic disorders.

Cystic fibrosis in Ontario.

The incidence of cystic fibrosis in Ontario, Canada has been determined from clinical data, from the cystic fibrosis database of the Hospital for Sick Children, Toronto, and from population statistics in the Province of Ontario. The survey included 420 confirmed cases of cystic fibrosis born during the period 1966-1980. The mean incidence during this period was one in 2,927. In the last 5-year period, a decline was noted in incidence that may have reflected in part the effectiveness of early diagnosis and genetic counseling in affected families. During the period of the survey, over 60% of cases were diagnosed within the first year of life, 74% by age 2 years, and 90% by age 5 years. Clinical diagnosis in the first year of life was more common in males (65%) than in females (54%), a consistent finding during the period of the survey. The incidence of meconium ileus was 15.7% of ascertained cases of cystic fibrosis, with similar incidences in males (16.4%) and females (14.4%). Although survival has not been the subject of this survey, mortality in the neonatal period was significantly higher in males than in females with cystic fibrosis.

Genetic aspects of immotile cilia syndrome.

The genetics of the immotile cilia syndrome has been analyzed in a series of 46 affected individuals from 38 families. Both sexes were equally affected: there were 20 males and 26 females in this series. All patients had upper and lower respiratory disease with chronic sinusitis, otitis, and chronic cough from early childhood. Bronchiectasis was common in older children and adults. Situs inversus occurred randomly, affecting 11 males and 15 females. Biopsies of nasal and bronchial mucosa from these subjects have been investigated by electron microscopy and identified as having specific ultrastructural defects of respiratory tract cilia including deficiencies in outer dynein arms (19), inner dynein arms (3), both inner and outer dynein arms (15), radial spoke defect (5); and microtubular transposition anomaly (4). Segregation analysis of proband sibships was consistent with autosomal recessive inheritance. However, the different ultrastructural defects that underly the immotile cilia syndrome involve presumably different genetic determinants, and the different types have not been analyzed separately. Examination of paternal age and birth order gave no evidence of new autosomal dominant mutation in the series.

Relationships among age-associated strength changes and physical activity level, limb dominance, and muscle group in women.

This study investigated the magnitude and rate of age-associated strength reductions in Australian independent urban-dwelling women and the relationship to muscle groups, limb dominance, and physical activity level. Independent urban-dwelling women aged 20 to 89 years (N = 217) performed maximal voluntary contractions with the dominant and nondominant knee extensors, plantar flexors, and handgrip. Anthropometric measurements were made and questionnaire responses used to obtain current physical activity levels. Trend analysis within analysis of variance and regression analysis on strength was performed. Limb muscle strength was found to be associated with increased age, muscle group, limb dominance, and activity. Self-reported physical activity levels declined with age but women who were more physically active for their age group were stronger in all muscle groups and had more lean body mass and lean thigh and leg cross-sectional area than relatively inactive women. Slopes of the linear reductions of maximal voluntary strength of the knee extensors, plantar flexors, and handgrip with age were significantly different (p < .05) at 9.3%, 7.4%, and 6.2% per decade, respectively. The limb muscle strength of healthy Australian independent and urban-dwelling women aged 20 to 89 years was found to be associated with age and three aspects of disuse: muscle group, relative levels of physical activity, and limb dominance.

Effect of training on eccentric exercise-induced muscle damage.

Eccentric muscle contractions generate delayed onset muscle soreness (DOMS), possibly as a result of the high tensions involved causing muscle damage. Muscle function, serum indicators of muscle damage, and DOMS were investigated throughout a training regimen that involved a 40-min eccentric walk down a 25% gradient on a treadmill at 6.4 km/h once a week for 8 wk. Serum creatine kinase and myoglobin concentrations were used as indicators of muscle damage, and both demonstrated a delayed increase after the exercise protocol. The muscles that contracted eccentrically exhibited low-frequency fatigue, as well as decreases in muscle fatigability and maximal voluntary contraction force, which were greatest immediately postexercise. Although the results show that training reduces DOMS, the serum muscle protein response, and muscle function impairment, the time courses of these adaptations are different. It is suggested that the function of the muscle can be impaired without apparent muscle damage.

Physiological responses to prolonged exercise in ultramarathon athletes.

The physiological responses of 10 ultramarathon athletes to prolonged exercise at the highest intensity level they could sustain for 4 h have been examined. Energy expenditure for the 4 h of exercise was 14,146 +/- 1,789 kJ, of which 63% was provided by the oxidation of fat. Plasma free fatty acids rose, but the changes in blood lactate concentration (delta 0.2 mmol/l) and exchange ratio (delta 0.05) were small, and the postexercise glycogen content (130 +/- 42 mumol/g) of the vastus lateralis muscles was estimated to be 37-53% of normal resting values. During exercise O2 intake (VO2) increased with time from the 50th to 240th min, the rise becoming significant (P less than 0.01) after 110 min of work. The change in VO2 was equivalent to a rise in relative intensity (%VO2max) of +9.1% and a change of speed of 1.49 km/h. A rise in cardiac frequency compensated for a fall in stroke volume (SV), so that cardiac output was maintained, and the increases in rectal temperature (Tre) (delta 0.63 degree C) and sweat loss (3.49 +/- 0.50 kg, equivalent to 5.5% of body wt) and the decreased mean skin temperature (Tsk) (-1.22 degree C) were within tolerable limits during exercise. Following exercise there was a loss (-25%) of ability to generate voluntary force of the quadriceps femoris, though electrically evoked mechanical properties of the muscle remained unchanged. The results suggest that neither thermal nor cardiovascular factors are limiting to prolonged (4 h) exercise, although the ability to utilize fat as a fuel may be important in ultradistance athletes.(ABSTRACT TRUNCATED AT 250 WORDS)

Intramyocellular triacylglycerol in prolonged cycling with high- and low-carbohydrate availability.

Vastus lateralis intramyocellular lipid (IMCL) content was assessed by (1)H-magnetic resonance spectroscopy before and after prolonged time trial cycling bouts of approximately 3-h duration. Six highly trained male cyclists completed a double-blind, randomized, crossover design of two experimental trials after a strenuous exercise bout and 48 h of high (HC) (9.32 +/- 0.08 g. kg(-1). day(-1)) and low (LC) (0.59 +/- 0.21 g. kg(-1). day(-1)) dietary carbohydrate. Resting IMCL content was significantly higher after LC vs. HC (P < 0.01) and was reduced during exercise by 64 and 57%, respectively. IMCL was not different between conditions after exercise (P > 0.05). The approximately twofold increase in IMCL degradation in LC compared with HC suggests that higher rates of whole body lipid metabolism in LC were in part attributable to a greater IMCL utilization. Four subjects experienced reductions of IMCL in excess of 70% during exercise. To our knowledge, this is the first study to report near depletion of IMCL during prolonged cycling, indicating that IMCL, presumably the triacylglycerol component, may be exhausted by prolonged strenuous exercise.

Human skeletal sarcoplasmic reticulum Ca2+ uptake and muscle function with aging and strength training.

This study investigated the adaptations of skeletal muscle sarcoplasmic reticulum (SR) Ca2+ uptake, relaxation, and fiber types in young (YW) and elderly women (EW) to high-resistance training. Seventeen YW (18-32 yr) and 11 EW (64-79 yr) were assessed for 1) electrically evoked relaxation time and rate of the quadriceps femoris; and 2) maximal rates of SR Ca2+ uptake and Ca2+-ATPase activity and relative fiber-type areas, analyzed from muscle biopsies of the vastus lateralis. EW had significantly slower relaxation rates and times, decreased SR Ca2+ uptake and Ca2+-ATPase activity, and a larger relative type I fiber area than did YW. A subgroup of 9 young (YWT) and 10 elderly women (EWT) performed 12 wk of high-resistance training (8 repetition maximum) of the quadriceps and underwent identical testing procedures pre- and posttraining. EWT significantly increased their SR Ca2+ uptake and Ca2+-ATPase activity in response to training but showed no alterations in speed of relaxation or relative fiber-type areas. In YWT none of the variables was altered after resistance training. These findings suggest that 1) a reduced SR Ca2+ uptake in skeletal muscle of elderly women was partially reversed with resistance training and 2) SR Ca2+ uptake in the vastus lateralis was not the rate-limiting mechanism for the slowing of relaxation measured from electrically evoked quadriceps muscle of elderly women.

Impaired calcium pump function does not slow relaxation in human skeletal muscle after prolonged exercise.

This study examined the effects of prolonged exercise on human quadriceps muscle contractile function and homogenate sarcoplasmic reticulum Ca2+ uptake and Ca2+-adenosinetriphosphatase activity. Ten untrained men cycled at 75 +/- 2% (SE) peak oxygen consumption until exhaustion. Biopsies were taken from the right vastus lateralis muscle at rest, exhaustion, and 20 and 60 min postexercise. Peak tension and half relaxation time of the left quadriceps muscle were measured during electrically evoked twitch and tetanic contractions and a maximal voluntary isometric contraction at rest, exhaustion, and 10, 20, and 60 min postexercise. At exhaustion, homogenate Ca2+ uptake and Ca2+ adenosinetriphosphatase activity were reduced by 17 +/- 4 and 21 +/- 5%, respectively, and remained depressed after 60 min recovery (P

Skeletal muscle metabolic and ionic adaptations during intense exercise following sprint training in humans.

The effects of sprint training on muscle metabolism and ion regulation during intense exercise remain controversial. We employed a rigorous methodological approach, contrasting these responses during exercise to exhaustion and during identical work before and after training. Seven untrained men undertook 7 wk of sprint training. Subjects cycled to exhaustion at 130% pretraining peak oxygen uptake before (PreExh) and after training (PostExh), as well as performing another posttraining test identical to PreExh (PostMatch). Biopsies were taken at rest and immediately postexercise. After training in PostMatch, muscle and plasma lactate (Lac(-)) and H(+) concentrations, anaerobic ATP production rate, glycogen and ATP degradation, IMP accumulation, and peak plasma K(+) and norepinephrine concentrations were reduced (P<0.05). In PostExh, time to exhaustion was 21% greater than PreExh (P<0.001); however, muscle Lac(-) accumulation was unchanged; muscle H(+) concentration, ATP degradation, IMP accumulation, and anaerobic ATP production rate were reduced; and plasma Lac(-), norepinephrine, and H(+) concentrations were higher (P<0.05). Sprint training resulted in reduced anaerobic ATP generation during intense exercise, suggesting that aerobic metabolism was enhanced, which may allow increased time to fatigue.