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Biomedical subjects

D R Lamb

Publications and source records attributed to D R Lamb.

At least 37 records · Page 2Linked to original sources
PubMed1990

Dietary carbohydrate and intensity of interval swim training.

We tested the effects of 9 d of a high-carbohydrate diet (80% of calories as CHO, 80% CHO diet) vs. a moderate-CHO diet (43% of calories as CHO, 43% CHO diet) on the abilities of collegiate swimmers to maintain a high intensity of interval swim training. Interval swim times and other physiological indices were recorded the last 5 d of each diet. Swim-interval distances ranged from 50-m interval sets to continuous 3000-m swims. There were no diet effects on mean swim velocities for any interval distance, and mean (+/- SEM) velocities for all swims were identical for both diets. There were no diet effects on the physiological indices; however, postswim blood lactate concentrations were higher after the 80% CHO diet. When mean +/- SEM daily caloric intake is 19.56 +/- 2.16 MJ (4675 +/- 516 kcal) for swimmers undertaking swim training to develop aerobic capacity, an 80% CHO diet provides no advantage over a 43% CHO diet for maintaining interval-swim-training intensity.

Adult↗
PubMed1990

Indomethacin suppresses the coronary flow response to hypoxia in exercise trained and sedentary rats.

STUDY OBJECTIVE: The aim was to determine if prostaglandin like activity might be involved in changes due to exercise training in the coronary flow responses to hypoxia. DESIGN: The coronary flow response to hypoxia was measured under constant perfusion pressure in isolated perfused hearts from 12 endurance exercise trained rats and 12 control rats. Eight hearts were perfused with a solution containing indomethacin, a cyclo-oxygenase inhibitor, to determine its effect on any training induced changes in the coronary flow response to hypoxic stress. EXPERIMENTAL MATERIAL: 24 male Sprague-Dawley rats, 517 (SD 51) g, were used for this study. The animals were anesthetised and the hearts rapidly excised and perfused with a modified Langendorff perfusion system. MEASUREMENTS AND MAIN RESULTS: Under constant perfusion pressure, the hearts of endurance exercise trained rats had a greater increase in coronary flow during hypoxia relative to normoxia than did hearts of untrained rats, at 13.52(2.15) v 9.56(1.05) ml.min-1.g-1 dry heart weight. Indomethacin treatment abolished this difference and lowered coronary flow: exercise -3.81(3.75) ml.min-1.g-1; control 0.38(2.44) ml.min-1.g-1. CONCLUSIONS: The inhibition by indomethacin of the endurance exercise training induced potentiation of the coronary fluid flow response to hypoxia suggests that prostacyclin or a related compound may be involved in this adaptation to exercise.

Animals↗
PubMed1988

Carbohydrate-electrolyte drinks: effects on endurance cycling in the heat.

On three occasions cyclists completed, as fast as possible, two exercise tasks (T1 and T2) separated by 30 min rest. T1 and T2 were equivalent to the work performed during 2 h cycling at 75% VO2max and 30 min at 75% VO2max, respectively. Every 20 min subjects drank 275 mL of a 6% (MC) or 2.5% (LC) carbohydrate-electrolyte beverage or a water placebo (P). The initial drink during both T1 and the rest period contained 20 g D2O as a marker for entry of ingested fluid into blood. No differences in drink effects were found for heart rate, sweat rate, change in plasma volume, rectal temperature, or D2O accumulation in blood. Blood glucose and respiratory exchange ratios were higher and T2 was performed faster with MC than with P. Ingestion of MC can help maintain blood glucose and enhance performance of prolonged cycling exercise without compromising fluid replenishment.

Adolescent↗
PubMed1987

Accumulation of deuterium oxide in body fluids after ingestion of D2O-labeled beverages.

A simple low-cost procedure was developed to compare the temporal profiles of deuterium oxide (D2O) accumulation in body fluids after ingestion of D2O-labeled solutions. D2O concentration was measured in plasma and saliva samples taken at various intervals after ingestion of 20 ml of D2O mixed with five solutions differing in carbohydrate and electrolyte concentrations. An infrared spectrometer was used to measure D2O in purified samples obtained after a 48-h incubation period during which the water (D2O and H2O) in the sample was equilibrated with an equal volume of distilled water in a sealed diffusion dish. The procedure yields 100% recoveries of 60-500 ppm D2O with an average precision of 5%. When compared with values for distilled water, D2O accumulation in serial samples of plasma and saliva was slower for ingested solutions containing 40 and 15% glucose and faster for hypotonic saline and a 6% carbohydrate-electrolyte solution. These differences appear to reflect known differences in gastric emptying and intestinal absorption of these beverages. Therefore this technique may provide a useful index of the rate of water uptake from ingested beverages into the body fluids.

Adult↗
PubMed1985

Opioid modulation of feeding behavior following forced swimming exercise in male rats.

Adult male rats were subjected to an acute bout of swimming exercise for 50 min during the early morning or late afternoon. Compared to nonexercised controls, all exercised groups showed an initial approximately 2-hr period of increased feeding (period I hyperphagia). A 50-min period of sham swimming (wading in water) was followed by period I hyperphagia but not period II hypophagia. Opioid modulation of period I hyperphagia was indicated by the ability of naltrexone to antagonize, in a dose-dependent manner, the postexercise hyperphagia. Furthermore, plasma concentrations of immunoreactive B-endorphin (Ir-B-ep) were increased during period I following exercise. Opioid modulation of the period II hypophagia was equivocal. Plasma Ir-B-ep was not altered in period II, and naltrexone did not modify period II hypophagia. The ability of 2-deoxy-D-glucose to induce feeding was slightly depressed (p less than 0.05) during period II after exercise, and the ability of exogenous insulin to induce feeding was not changed. These differential feeding responses to 2-deoxy-D-glucose (opioid-mediated) and insulin (relatively opioid-independent) suggest that an opioid deficiency may exist during period II and contribute to the hypophagia.

Animals↗
PubMed1985

Opioid modulation of feeding behavior following repeated exposure to forced swimming exercise in male rats.

Patterns of normal and stimulated food intake (FI) as well as its possible endogenous opioid (EO) modulation were investigated in male rats given regular swimming exercise (trained; TR) and compared with nonexercised sedentary (SED) controls. Rats in the TR group had lower body weights as well as reduced 24 hr FI due to lower nocturnal FI. TR rats also ate less food in response to injections of 2-deoxy-D-glucose (2-DG) but not insulin (INS) when injections were given during the first 4-5 weeks of training. However, this difference between TR and SED rats in the 2-DG induced feeding was not demonstrable after 10 or more weeks of training. Plasma concentrations of immunoreactive B-endorphin (IR-B-ep) were elevated, as expected, in TR rats (10-12 weeks) during nocturnal sampling whereas the nocturnal increase of IR-B-ep was absent in SED controls. However, these SED rats did increase daytime IR-B-ep in response to 2-DG and acute exercise, albeit somewhat less in magnitude when compared to TR rats. Injection of naltrexone (NTX) decreased feeding in TR rats (10-12 weeks) but not in contemporary SED controls. In summary, exercise training modified feeding behavior, and at 4 weeks of training, TR rats ate less in response to opioid-related feeding stimulus of 2-DG, but responded similarly to insulin (relatively opioid independent) treatment. At later stages of training this difference between TR and SED rats disappeared. Moreover, SED rats had atypical profiles of IR-B-ep and reduced hypophagic responses to NTX suggesting that TR rats might have greater EO modulation of feeding at this stage.

Animals↗
PubMed1984

Myofibrillar protein degradation after eccentric exercise.

Male rats were run downhill for 90 minutes (nonexhaustive). Following the exercise, muscle protein degradation was increased, as determined by urinary 3-methylhistidine. However, minimal changes were observed in the relative percentage of the minor myofibrillar proteins and in the protease calcium activated factor in the long head of the triceps brachii muscle (eccentrically exercised) following the exercise bout.

Animals↗
PubMed1982

Effects of physical training on hypothalamic obesity in rats.

Forty-eight male rats either underwent sterotaxic placement of electrolytic lesions in the ventromedial nucleus of the hypothalamus or had a sham operation and, after a recovery period of at least two weeks, were assigned to either a trained or untrained condition. Training consisted of treadmill running for 120 min per day, 5 days per week, for 12 weeks. At which point all rats were sacrificed to allow the determination of carcass analysis and fat pad lipolysis rates. Both untrained and trained animals with lesions had significantly increased carcass fat. The increased fat content not be attributed to an increased intake since the average daily food consumption of the four groups was not different. Training significantly reduced the fat content in both the lesioned and unlesioned rats. However, the loss in the lesioned rats was about one third less than that of the unlesioned. Training also increased the rate of lipolysis irrespective of whether an animal was lesioned or not. However, the amount of increase was about one third less than in trained normals. Destruction of the ventromedial nucleus of the hypothalamus apparently does not destroy the ability of exercise to alter body composition. The lesions may diminish the capacity of endurance programs to reduce carcass fat. Since the findings relative to lipolysis result from an in vitro investigation, they do not necessarily reflect the events occurring in the in vivo state.

Animals↗
PubMed1981

Modified assays to detect activation of glycogen synthase following exercise.

Glycogen levels and glycogen synthase activity were measured in red vastus lateralis muscle of male Sprague-Dawley rats killed at rest, immediately after swimming to exhaustion, or 4 h postexhaustion. Glycogen levels were very low immediately after the exercise but returned to preexercise levels after 4 h of recovery. Activation of glycogen synthase by glucose 6-phosphate (G6P) was determined in the standard assay of Thomas et al. (Anal. Biochem. 25: 486-499, 1968) using 4.4 mM uridine diphosphate glucose (UDPG) (pH 7.8) or in a modified assay using 0.03 mM UDPG (pH 6.9) in the absence or presence of inhibitor (inorganic phosphate or uridine 5'-diphosphate). Activation of glycogen synthase was determined by measuring activity ratio (activity in the absence of G6P divided by activity in the presence of G6P), A0.5 for G6P (concentration of G6P producing half-maximal activation), and fractional velocity (activity with low G6P divided by activity with high G6P). All three measurements indicated glycogen synthase was significantly activated immediately after exhaustion. Activation after 4 h of recovery was not detected using activity ratio but was readily apparent when fractional velocity of A0.5 for G6P were measured.

Animals↗
PubMed1979

Glycogen synthase activation in human skeletal muscle: effects of diet and exercise.

We investigated the role of glycogen synthase in supranormal resynthesis (supercompensation) of skeletal muscle glycogen after exhaustive exercise. Six healthy men exercised 60 min by cycling with one leg at 75% VO2max, recovered 3 days on a low-carbohydrate diet, exercised again, and recovered 4 days on high-carbohydrate diet. Glycogen and glycogen synthase activities at several glucose-6-phosphate (G6P) concentrations were measured in biopsy samples of m. vastus lateralis. Dietary alterations alone did not affect glycogen, whereas exercise depleted glycogen stores. After the second exercise bout, glycogen returned to normal within 24 h and reached supercompensated levels by 48 h of recovery. Glycogen synthase activation state strikingly increased after exercise in exercised muscle and remained somewhat elevated for the first 48 h of recovery in both muscles. We suggest that 1) forms of glycogen synthase intermediate to I (G6P-independent) and D (G6P-dependent) forms are present in vivo, and 2) glycogen supercompensation can in part be explained by the formation of intermediate forms of glycogen synthase that exhibit relatively low activity ratios, but an increased sensitivity to activation by G6P.

Adult↗
PubMed1976

Structure and function of cardiac mitochondria in exhausted guinea pigs.

The ultrastructure and functional capacity of mitochondria from hearts of exhausted guinea pigs were compared to those from rested animals. Electron micrographs of heart ventricles were examined for ultrastructural alterations, and functional capacity was studied by oxygen polarography. General swelling of mitochondria from exhausted animals was indicated by a 41% reduction in mitochondrial surface/volume ratio and a 22% increase in volume density of mitochondria from exercised animals when compared to those from controls. The yield of isolated mitochondria from exhausted guinea pigs was similar to that for control animals. In the presence of all substrates tested the rate of oxygen consumption was lower in the exhausted animals than in the controls. The ADP/O ratios and respiratory control indices for pyruvate, succinate and ascorbate were not systematically affected by exercise. With glutamate as substrate respiratory control was reduced in exercised guinea pigs. These experiments suggest that the structure of myocardial mitochondria from exhausted animals is sufficient to maintain normal ADP/O ratios but is not adequate to maintain normal rates of respiration.

Animals↗
PubMed1975

Skeletal muscle leucine incorporation and testosterone uptake in exercised guinea pigs.

We examined the changes induced by daily treadmill exercise on body weights, plantaris muscle weights, plantaris protein concentrations, and L-leucine-4,5-3H incorporation into plantaris muscles of normal and castrated young male guinea pigs and of castrated animals receiving testosterone replacement therapy, and compared the testosterone-1,2-3H uptake by plantaris muscles of trained normal guinea pigs to that of untrained animals. Trained animals exhibited significantly lower body and muscle weights and greater labeled leucine incorporation into sarcoplasmic and myofibrillar proteins but did not show significant changes in protein concentrations or labeled testosterone uptake. The level of physical activity of the young animals studied appeared to be more important than gonadal endocrine function in altering protein metabolism and muscle and body weights. Because hypertrophy did not occur in the trained plantaris muscles, which had elevated rates of labeled leucine incorporation, it appears that the trained animals had a higher muscle protein turnover rate. It seems unlikely that testosterone plays an important role in these activity-related phenomena.

Animals↗
PubMed1975

Glycogen replenishment following exercise: effects of denervation and tenotomy.

To examine the role of the nervous system in the rapid replenishment of muscle glycogen that occurs after exhaustive exercise, glycogen stores and glycogen synthetase activity of normal gastrocnemius muscles of untrained and trained guinea pigs were compared to glycogen and synthetase activity of trained gastrocnemius muscles that were denervated or tenotomized immediately after exhaustive exercise and then allowed to recover for 48 h. The trained tenotomized muscles, but not the denervated muscles, had significantly (P smaller than 0.05) less glycogen than the trained normal muscles. These results suggest that neither nerve impulse conduction nor tropic substances contained in neural tissue proximal to the site of denervation mediate glycogen replenishment after exercise. The active, glucose 6-phosphate independent (I) form of glycogen synthetase activity was reduced by both denervation and tenotomy at 48 h after exercise with no significant (P greater than 0.05) differences detected for the total of I and D (glucose 6-phosphate dependent) synthetase activity. Synthetase I relative to total synthetase activity was similar in trained and untrained normal muscles, both of which had significantly (P smaller than 0.05) greater relative I activities than denervated or tenotomized muscles. These synthetase data show that elevated glycogen stores following recovery from exercise may be observed in the absence of increased levels of glycogen synthetase activity.

Achilles Tendon↗
PubMed1975

Androgens and exercise.

In this presentation several of the reasons why androgenic hormones might be responsible for some of the effects of physical training and for some of the differences among individuals in athletic ability have been outlined. It seems apparent that minimal amounts of androgen are necessary to produce the normal differences between males and females in aggression, red blood cell production and bone growth, but it seems unlikely that any additional natural androgen, perhaps produced as a result of physical training, can be shown to enhance these characteristics after puberty. It seems more likely that changes in androgen levels or changes in sensitivity to androgens may be shown to be involved in the increases in muscle glycogen, protein synthesis, and lean body mass associated with chronic exercise. However, the data suggesting changes in androgen levels or androgen uptake with exercise are so meager and contradictory that no complete answer to any of these problems can yet be offered. Perhaps the best evidence that androgens are involved in athletic performance is that boys become more athletically proficient than girls at puberty, the time of the greatest changes in blood testosterone. The changes in muscle strength, body weight and lean body mass caused by anabolic steroid treatment are probably greater than many would hope and somwhat less than many think. There is apparently a wide range of individual responses to these drugs.

Adrenal Glands↗
PubMed1975

Postexercise glycogen replenishment in untrained animals: denervation, tenotomy effects.

To test the hypothesis that an intact nerve supply is essential to normal replenishment of muscle glycogen after exhaustive exercise, glycogen concentration in normal gastrocnemius muscles from guinea pigs exhausted 48 hr previously was compared to glycogen in contralateral muscles that had been denervated at the muscle or high in the thigh immediately after exercise. Each animal of another group underwent tenotomy of one Achilles tendon after exercise so that any effect of disuse could be distinguished from effects of denervation. All muscles were able to replenish glycogen to normal control values 48 hr after exercise and surgery; there were no significant (greater than .05) effects of any of the surgical interventions. Therefore, it appears that glycogen concentration in skeletal muscle 48 hr after exhaustive exercise is independent of both neural phenomena and muscle tension.

Animals↗