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In a previous study we observed that one day of food restriction caused an increase in the rate of total muscle protein degradation and that this increase could be prevented by a bout of exercise. The present study was conducted to determine if this effect occurred after 15 days of exercise and food restriction. The rate of muscle protein degradation was determined using the perfused rat hindlimb model by measuring the rates or release of tyrosine and 3 methylhistidine. In contrast to our previous study, food restriction resulted in a decreased rate of total skeletal muscle protein degradation, and moderate exercise did not affect the rate of protein degradation in either the food restricted or ad lib fed rats. Thus, it would appear that moderate regular exercise has little or no affect on the rate of skeletal muscle protein degradation either alone or together with food restriction.

The purpose of this study was to examine the effect of exercise on the rate of protein degradation in rat skeletal muscle. The rates of total and myofibrillar protein degradation were determined by the measurement of the rates of release of tyrosine and 3-methylhistidine, respectively, from the perfused single rat leg. This method measures the rate of protein degradation in the entire lower leg and does not suffer from the limitations inherent in methods that rely on urinary excretion. The rate of total protein degradation was increased by exercise and involved increased flux through the lysosomal pathway, while the breakdown of myofibrillar protein was unchanged. The changes in the rates of protein degradation during the recovery period were greatly influenced by energy intake. Again the rate of myofibrillar protein degradation was unchanged or slightly increased during the recovery period, after either level or downgrade running. Exercise did prevent the increase in the rate of total protein degradation caused by food restriction, which may have important implications in weight reduction diets.

Gluconeogenic enzymes were assayed after varying periods of exercise and recovery to determine how rapidly changes occur and whether they persist after the cessation of exercise. Untrained male rats (250 g) ran on a treadmill at 28 m/min and were killed after varying periods of exercise and recovery. Livers were quickly removed and analyzed for maximal enzyme activities (saturating levels of substrate) and submaximal activities (low-substrate concentrations). The most significant enzyme changes during exercise were increased maximal activity of phosphoenolpyruvate carboxykinase (PEPCK) and decreased submaximal activity of phosphofructokinase (PFK). Submaximal PFK activity was decreased by 30 min of exercise and remained at that low level up to exhaustion (172 +/- 16 min). Changes in submaximal PFK activity are in response to decreased concentrations of fructose-2,6-bisphosphate that were decreased to approximately one-tenth the control value after 30 min of exercise and remained low throughout exercise and 1 h of recovery. The PEPCK activity progressively increased during exercise and was highest at exhaustion. The cAMP level was significantly elevated in liver of rats exercised for 30 min and continued to rise with duration. Six hours after exercise PEPCK and submaximal PFK activities were the same in control and exercised-rested rats. The change in PEPCK activity is consistent with an increase in the rate of enzyme synthesis and/or a decrease in enzyme degradation during exercise, whereas the lowered activity of PFK likely reflects covalent modification of 6-phospho-fructo-2-kinase/fructose-2,6-bisphosphatase.

The influence of exhaustive exercise on the capacity of liver and muscle of rats to oxidize fatty acids was investigated in vitro. The rate of oxidation of fatty acids by liver preparations was significantly elevated as a result of exhaustion. Concurrently, the concentrations of beta-hydroxybutyrate were elevated in the plasma of the exhausted rats, suggesting that oxidation of fatty acids was also elevated in vivo. These findings are analogous to the findings of increased oxidation of fatty acids that results from training. In muscle, oxidation of palmitate, palmitoylcarnitine and beta-hydroxybutyrate by homogenates and isolated mitochondria was depressed with exercise. Despite the decrease in the oxidative capacity of the muscle preparations, the activities of several enzymes of beta-oxidation were either increased or unchanged as a result of exercise, suggesting that the depression in fatty acid oxidation may not be related to alterations in the process of beta-oxidation. Further studies showed that oxidation of [2-(14)C]pyruvate by muscle was depressed, whereas oxidation of [1-(14)C]pyruvate was not changed as a result of exercise. These results suggest that the decrease in fatty acid oxidation may be related to aberrations in the oxidation of acetyl-CoA. The changes in fatty acid oxidation that were observed, which are at variance with what is reported to occur with training, may have resulted from increased fragility of muscle mitochondria as a result of exercise. This increased fragility may render the mitochondria more susceptible to experimental manipulations in vitro and a subsequent loss of normal function.

The effects of daily maternal exercise on fetal-placental growth and development and the associated changes in uteroplacental blood flow were studied in pregnant rats. Pregnant females were exercised for 1 h (0% grade at 28 m/min) daily between either days 1 and 12, 1 and 18, 1 and 22, 12 and 18, or 12 and 22 of gestation and compared with nonexercised controls. Exercise between days 1 and 12 of pregnancy had no effect on fetal-placental parameters (i.e., fetal weight or gestation length) relative to controls. In contrast, exercise between days 1 and 22 and 12 and 22 resulted in a lower number of live pups born, an increase in gestational length, and an increased birth weight of the live pups relative to controls. Exercise between days 1 and 18 or 12 and 18 induced a significant (p less than or equal to 0.05) suppression of uteroplacental blood flow, the number of viable fetuses, and placental weights as compared with controls. Daily exercise had no effect on ovarian function as indicated by the comparable serum progesterone levels in all groups. These data indicate that an exercised-induced depression of uteroplacental blood flow is related to impaired fetal-placental growth and development during pregnancy in the rat.

Branched-chain keto acid (BCKA) dehydrogenase activity was examined in rat skeletal muscle as a function of exercise intensity and nutritional status. The activity of BCKA dehydrogenase increased with increasing exercise intensity, showing increases over resting values of 76, 172, and 245% at 10, 20, and 30 m X min-1. The exercise-induced increase in BCKA dehydrogenase activity was the same in the gastrocnemius and in the quadriceps muscles. Rapid removal of the muscle after death is essential because the activity of BCKA dehydrogenase decreased rapidly after death. Thus the likely reasons Wagenmakers et al. (Biochem. J. 223: 815–821, 1984) found exercise caused a much smaller increase in BCKA dehydrogenase activity than Kasperek et al. [Am. J. Physiol. 248 (Regulatory Integrative Comp. Physiol. 17): R166–R171, 1985] are differences in muscle removal time and the duration of exercise. Starvation for 24 h before exercise increased the exercise-induced activation of BCKA dehydrogenase by 160%, which suggests that the increased BCKA dehydrogenase activity is in response to an increased requirement for citric acid cycle intermediates.

We recently observed that a 24-h fasted group of rats could run longer than an ad libitum fed control group before becoming exhausted. Because of the demonstrated importance of glycogen levels and free fatty acid availability during endurance exercise, we have investigated several parameters of carbohydrate and lipid metabolism in exercised and nonexercised rats that were either fed ad libitum or fasted for 24 h. A 24-h fast depleted liver glycogen, lowered plasma glucose concentration, decreased muscle glycogen levels, and increased free fatty acid and beta-hydroxybutyrate concentrations in plasma. During exercise the fasted group had lower plasma glucose concentration, higher plasma concentration of free fatty acids and beta-hydroxybutyrate, and a lower muscle glycogen depletion rate than did the ad libitum fed group. Since fasted rats were able to continue running even when plasma glucose had dropped to levels lower than those of fed-exhausted rats, it seems unlikely that blood glucose level, per se, is a factor in causing exhaustion. These results suggest that fasting increases fatty acid utilization during exercise and the resulting “glycogen sparing” effect may result in increased endurance.

The purpose of the present investigation was twofold: (i) to develop a simple and reliable method for measuring muscle protein synthesis in vivo and (ii) to use the method to study the effect of exercise on muscle protein synthesis. The method that has been developed is based on the principle that [ 3 H]tyrosine is released at a fairly constant rate from a subcutaneously injected emulsion of water and sesame oil. Incorporation of label into muscle protein and [ 3 H]tyrosine specific activity are linear for at least 60 min. Thus, removing muscle samples at two time periods (30 and 60 min) allows the rate of muscle protein synthesis to be determined. In a previous study, we found that swimming rats for 1 hr resulted in an 18% reduction in the rate of protein synthesis. In the present study, 1 hr or running resulted in a 30% depression while running to exhaustion caused a 71% depression in muscle protein synthesis. These results indicate that muscle protein synthesis changes in response to the intensity and the duration of an exercise bout.

Exhaustive treadmill running caused a significant decrease in hepatic protein levels. The rate of protein loss was 0.23 g/hr. This protein loss was accompanied by an increase in the activities of free (nonsedimentable) cathepsin D and arylsulfatase, suggesting the involvement of lysosomes. A 24-hr fast lowered the liver protein levels by about 20%. Plots of liver protein levels versus the time it took to reach exhaustion showed that the absolute rate of protein loss was the same for both the fed and the fasted rats. Since the initial protein levels were lower in the fasted rats, their relative rate of protein loss was greater. The level of activity of free (nonsedimentable) cathepsin D and arylsulfatase increased as the time to exhaustion increased in both the fed and fasted animals. The increase was severalfold greater in the fasted animals suggesting that fasting alters the structure of lysosomes in a way that enhances the increase in lysosomal fragility caused by exercise.

The levels of the branched-chain amino and oxo acids were measured in muscle and plasma after exercise and 10 min postexercise. Leucine was increased in both muscle and plasma after exercise and 10 min postexercise. The muscle levels of the branched-chain oxo acids were not increased immediately after exercise but were increased 10 min postexercise. Exercise caused a large increase in the plasma levels of the oxo acids of leucine and isoleucine that was further increased 10 min postexercise. The activity of branched-chain 2-oxo acid dehydrogenase (BCOAD) was increased immediately after exercise but returned to the control value by 10 min postexercise. The lack of correlation between the muscle and plasma levels of the branched-chain amino and oxo acids and BCOAD activity suggests that these amino and oxo acids are not the primary physiological regulators of BCOAD activity during exercise. On the other hand, an excellent correlation was found between the muscle ATP level and BCOAD activity, with the ATP content decreasing in tandem with an increase in BCOAD activity during exercise and decreasing during the recovery period after exercise.

The effect of exercise on the rate of total and myofibrillar protein degradation was determined by measuring the rate of release of tyrosine and 3-methylhistidine, respectively, from isolated rat soleus muscle strips after exercise. The rate of tyrosine release was 30–50% greater from the muscles of the exercised rats, whereas the rate of 3-methylhistidine release was unchanged. Thus the exercise-induced increase in the rate of protein degradation is due to increased breakdown of nonmyofibrillar proteins. The rate of protein degradation increases as a function of exercise duration and rapidly returns to the preexercise level during recovery. The exercise-induced increase in the rate of protein degradation is not inhibited by chloroquine. Together these observations suggest that the increase in the rate of protein degradation observed immediately after exercise is due to the breakdown of nonmyofibrillar proteins and occurs via the nonlysosomal pathway of protein degradation.

Previous reports have shown that exercise causes a loss of liver protein. The purpose of the present study was to elucidate the mechanism of this exercise-induced protein loss. Exercise caused: (1) an increase in mechanical and osmotic lysosomal fragility; (2) a significant loss of hepatic water, glycogen, protein, phospholipid and RNA; (3) loss of protein from the soluble, mitochondrial and microsomal fractions: (4) loss of mitochondrial, microsomal and cytosolic, but not lysosomal, enzyme activity; (5) an increase in the number of autophagic vacuoles; (6) an increase in the lysosomal size. Taken together, these results suggest that the autophagolysosomal system is responsible for the exercise-induced hepatic protein loss.

The present study was conducted to investigate the metabolic regulation of leucine oxidation during exercise. Ten rats per group were run at 27 m/min (0% grade) on a treadmill for 30 and 120 min or until exhausted, and the total and basal activity of branched-chain keto acid dehydrogenase was examined in the muscle, liver, and heart. The total activity of the dehydrogenase in the heart, liver, or skeletal muscle was unchanged by exercise. However, exercise increased the basal activity levels of the dehydrogenase about 10-fold in muscle and 5-fold in heart. The basal dehydrogenase activity in the liver was unchanged by exercise. Activation of the dehydrogenase in both muscle and heart was statistically elevated after 30 min exercise and continued to increase during the remainder of the exercise bout. The basal activity of the dehydrogenase returned to resting levels by 10 min postexercise. The activation of the dehydrogenase in muscle and heart during exercise likely is due to dephosphorylation because activity of the enzyme in mitochondria isolated from exercised muscles reverts to control values when the mitochondria are incubated in the presence of ATP. Thus the increased leucine oxidation observed during exercise is due to activation of the branched-chain keto acid dehydrogenase by dephosphorylation. This is the first example of a large increase in branched-chain keto acid dehydrogenase activity caused by a physiological process. This demonstrates that the muscle's latent capacity of oxidize branched-chain amino acids is much larger than previously thought and that this capacity is used in exercising muscle.

These experiments were undertaken in order to investigate the changes in protein synthesis and degradation which result from physical training in male and female rats. Protein synthesis and protein degradation were measured in perfused hemicorpus preparations from trained and untrained male and female rats. Additionally, the activities of several muscle proteinases were measured. The rates of protein synthesis and degradation were greater in females than in males. Protein degradation was increased by training in males but not in females. There were no changes in protein synthesis rates due to training in either sex. Myofibrillar alkaline proteinase was observed to be more active in females than in males, but there were no changes in levels of muscle proteinases as the result of training. Since we observed that exercise training resulted in a decreased rate of weight gain in male rats but not in female rats, it seems that the differences in protein metabolism observed between males and females contribute to the difference in growth rate response to endurance training.

Several reports have shown that amino acid utilization via oxidation and gluconeogenesis is increased during exercise. The purpose of this study was to investigate whether these changes are accompanied by alterations in protein synthesis and degradation in the muscle of exercising rats. One group of rats was made in swim for 1h and then protein synthesis and protein degradation were measured in a perfused hemicorpus preparation. Protein synthesis was decreased and protein degradation was increased in exercised rats compared with sedentary control rats. Exercise also decreased amino acid incorporation by isolated polyribosomes from muscle. Measurement of several muscle proteinase activities demonstrated that exercise had no effect on alkaline proteinase or Ca2+-activated proteinase. However, the free (unbound) cathepsin D activity was elevated in muscle of exercised rats, whereas the total activity of catepsin D was unchanged. This increase in the proportion of free cathepsin D activity suggests that lysosomal enzymes may be involved in the increased protein degradation that was observed.

Glucose-6-phosphate dehydrogenase and N-acetyl-beta-glucosaminidase activities were both elevated after eccentric exercise indicating that this type of exercise causes muscle damage. Muscle damage as measured by glucose-6-phosphate dehydrogenase activity in the vastus intermedius was greater and occurred later in larger rats indicating that the susceptibility to muscle damage is increased and the repair process delayed in older and larger animals.

The purposes of these experiments were to compare the activities of glucose 6-phosphate dehydrogenase (G6PDH) and the lysosomal enzyme N-acetyl-beta-glucosaminidase (NAG) in rat muscles and to assess protein degradation after eccentric exercise (running down a 18 degrees grade). The following results were obtained: (1) Muscles in which the G6PDH activity was increased also showed an increase in NAG activity that was smaller and occurred later and/or was more prolonged than the increase in G6PDH activity. (2) The urinary 3-methylhistidine/creatinine ratio was statistically elevated for 3 days after eccentric exercise and this increase was much larger and more prolonged than previously observed in rats run on the level. Taken together our results suggest that increased protein degradation after exercise is due to increased proteolysis of muscle tissue damaged during the exercise bout and that lysosomal enzymes may be involved in this degradation.

Pyruvate dehydrogenase and phosphoenolpyruvate carboxykinase are important enzymes in the regulation of muscle pyruvate metabolism and their in vitro measured activities have been studied in muscle from rested and exercised rats. In addition, the muscle concentration of metabolic intermediates associated with pyruvate metabolism has been measured after exercise. Phosphoenolpyruvate concentration was decreased to less than half the value found in rested muscle but pyruvate concentration did not change. This suggests an increase in the in vivo rate of conversion of phosphoenolpyruvate to pyruvate. Concentrations of malate and aspartate increased two- to threefold which suggests that oxaloacetate concentration was also increased. An increase in oxaloacetate availability would increase acetyl CoA metabolism and therefore would increase pyruvate dehydrogenase activity in vivo. The basal activity of pyruvate dehydrogenase measured in vitro increased approximately twofold after 2 hr of exercise and returned to control values 5 min after the cessation of exercise. Total pyruvate dehydrogenase activity (activated to the maximal extent) was not changed by exercise. Muscle PEPCK activity was also increased during exercise suggesting an increased rate of conversion of oxaloacetate to pyruvate to provide net oxidation of oxaloacetate and other citric acid cycle intermediates. Results of this study demonstrate that the rates of formation and metabolism of pyruvate are increased during exercise.

This study was undertaken to determine the effects of increasing exercise time until exhaustion on the capacity of liver to synthesize and oxidize fatty acids, as well as the capacity of muscle to oxidize fatty acids. Additionally, the same parameters were examined during various periods of recovery after exhaustion. These studies were prompted by the scarcity of information relating the effects of exercise on the metabolism of fatty acids in liver, and by our findings and those of others where exhaustive exercise was reported to cause a decrease in the capacity of muscle to oxidize fatty acids. The latter led to the hypothesis that the reported decrease in fatty acid oxidation may be a factor in fatigue. Thus the purpose of the present studies was threefold. The first was to determine changes in fatty acid metabolism in liver during exercise and recovery; the second was to test the above hypothesis by following time-course changes of fatty acid oxidation by muscle; and the third was to determine whether or not the effects of exhaustion are reversible. The results obtained showed that fatty acid synthesis in liver decreased with increasing time but returned to normal levels by approximately 12 hr of rest after exhaustion. Oxidation of fatty acids by liver remained unchanged during the first hour of exercise but steadily increased afterwards until it reached a maximum at exhaustion. Oxidation returned to control level after 12 hr of rest and remained so during the subsequent recovery period. Fatty acid oxidation by muscle was maximally depressed after 1 hr of exercise, yet the animals continued to run, thus ruling out the possibility that the decreased oxidation of fatty acids with exhaustion is a factor in fatigue. Finally, recovery studies showed that the biochemical processes that were examined returned to control levels within 12–24 hr after exercise demonstrating that these effects are not permanent.

The rate of protein degradation was found to be increased in isolated soleus and extensor digitorum muscles of 60–80 g rats after exercise consisting of running for 120 min. These findings support the hypothesis that exercise causes an increase in skeletal muscle protein degradation, and that both red and white muscles are affected similarly.

Kinetics of aromatization of 1,4-dimethylbenzene oxide ( I ) to 2,5-dimethylphenol ( II ) and 2,4-dimethylphenol ( III ), the latter arising by an NIH-Shift of a methyl group, as measured in the pH range 1-12, follow the equation - d [ I ]/ dt = [ I ][ k 0 + ( k [unk] + k [unk]) a H], where k 0 = 4.8 × 10 -3 sec -1 , k [unk] = 7.3 × 10 2 M -1 sec -1 , and k [unk] = 5.3 × 10 2 M -1 sec -1 . The ratio of products II to III at pH ≥ 6 in the spontaneous rearrangement ( k 0 ) is 13 to 87, and changes to 54 to 46 in the acid-catalyzed rearrangement ( k [unk] and k [unk]). While no intermediate is detectable in the acid-catalyzed rearrangement of the arene oxide by pathway k [unk], simultaneous addition of water (and other nucleophiles) by pathway k [unk] leads, via the intermediate 1,4-dimethyl-2,5-cyclohexadiene-1,4-diol ( IV ), to the phenols II and III . This new mechanism for the NIH-Shift serves as a model for the ease of nucleophilic addition to other arene oxides, such as those of the polycyclic aromatic hydrocarbons recently implicated in mechanisms of carcinogenesis.

During endurance exercise, there is a net breakdown of body protein and the amino acids so mobilized are available for increased rates of oxidation and gluconeogenesis. At least part of the net loss of protein is due to a decrease in the rate of protein synthesis during exercise. Liver protein degradation is increased during exercise as a result of autophagy and proteolysis of cell material inside the secondary lysosomes. The rate of degradation of contractile proteins is decreased during exercise but is increased during the recovery period if the exercise is of high intensity and of long duration. Preliminary evidence suggests that the rate of degradation of non-contractile proteins in muscle may be increased at the same time that contractile protein degradation is decreased.

This experiment examines the fumarase catalyzed conversion of L-malate into fumarate as followed by a proton magnetic resonance spectrometer.

In order to differentiate between the kinetically equivalent mechanisms of either concerted proton migration and epoxide ring opening or stepwise formation of carbonium ion followed by proton migration to form in either case the keto form of the phenol, the primary kinetic isotope effects for aromatization of perdeuteriodihydroepoxybenzene and [1-2H]dihydro-1,2-epoxynaphthalene (kH/kD=ca. 1) as well as the substituent effects on the rate for benzene epoxide (ρ–7·3 and –7·6 for spontaneous and acid-catalysed paths, respectively) have been determined; the stepwise mechanism is strongly favoured.

The reaction of dimethyl trans-1,2-dihydrophthalate (I) and dimethyl 1,4-dihydrophthalate (II) with a series of flavins involves reaction of the common dimethyl dihydrophthalate carbanion and flavin(s) within a face-to face complex not unlike that formed between flavin and tryptophan; the 10a-position is not involved in this reaction and is not likely involved in the reoxidation of the flavins by O2.