Biomedical subjects

D A Essig

Publications and source records attributed to D A Essig.

27 records · Page 2Linked to original sources

PubMed1991

Expression of embryonic myosin heavy chain mRNA in stretched adult chicken skeletal muscle.

Chronic stretch of the chicken fast-twitch patagialis muscle increases the rate of growth and percentage of fast-twitch oxidative fibers. We have analyzed the effects of stretch on the expression of two previously identified "embryonic" myosin heavy chain (MHC) mRNAs (p251 and p110). Both MHC mRNAs were expressed in the patagialis at their highest levels in the embryo and 1 wk after hatching. During posthatch development (7-52 wk), the p110 mRNA was expressed in only trace quantities while the p251 mRNA was not detectable. After 2 wk of stretch of the patagialis in 7- or 38-wk-old birds, the p110 mRNA was increased to levels similar to that found in patagialis of newly hatched chicks, whereas expression of the p251 transcript was not affected. The existence of two other MHC mRNAs homologous to the p110 mRNA was suggested by the S1 mapping analysis, one of which was expressed at dramatically reduced levels in the stretched patagialis. It is concluded that stretch can cause selective alterations in the expression of developmentally regulated MHC isoforms in chicken fast-twitch muscle.

Aging↗

PubMed1991

Muscle-specific regulation of the heme biosynthetic enzyme 5'-aminolevulinate synthase.

The induction of 5'-aminolevulinate synthase (ALV synthase) activity in adult muscle by overload occurs in the absence of proportional changes in its mRNA content. Complete interpretation of these findings is difficult because little is known of the basal regulation of ALV synthase expression in muscle. In three adult chicken muscle fiber types (n = 5 each), differences in ALV synthase activity were correlated (r greater than or equal to 0.89; P less than 0.05) to the activities of cytochrome oxidase (COX) and citrate synthase (CS) and to levels of the "liver" isoform of ALV synthase mRNA. During posthatch development, ALV synthase activity and mRNA levels (n = 3-6 per time point) also covaried with changes in COX and CS activity. The highest levels of ALV synthase mRNA in muscle are observed early in myogenesis prior to induction of COX activity. The regulation of ALV synthase is also tissue-specific because the higher basal levels of ALV synthase activity in liver mitochondria are associated with disproportionately less oxidative enzyme activity and less of the liver ALV synthase isoform mRNA than in muscle.

5-Aminolevulinate Synthetase↗

PubMed1990

Differential regulation of actin and myosin isoenzyme synthesis in functionally overloaded skeletal muscle.

Overload hypertrophy of the chicken anterior latissimus dorsi muscle is accompanied by a replacement of one myosin isoenzyme (slow myosin-1, SM1) by another (slow myosin-2, SM2). To investigate the molecular mechanisms by which these changes occur, we measured the fractional synthesis rates (ks) in vivo of individual myosin-heavy-chain isoenzymes, total actin and total protein during the first 72 h of muscle growth. Although the ks of total protein and actin were doubled at 24 h, the ks for SM1 and SM2 were depressed. However, the ks of both isomyosins were nearly tripled by 72 h. Despite the increase in muscle size observed at 72 h, the amount of SM1 was reduced by half, indicating increased degradation of SM1. Results of translation of polyribosomes in vitro paralleled the results obtained in vivo. The proportion of total polyadenylylated mRNA in total RNA was increased at 48 and 72 h, but unchanged at 24 h despite the increase in protein synthesis at 24 h. Nuclease-protection analyses indicate that the level of specific SM1 and SM2 mRNAs change in a reciprocal fashion during overload. We conclude that gene-specific and temporal differences exist in the regulatory mechanisms that control overload-induced muscle growth.

Actins↗

PubMed1990

Regulation of 5'-aminolevulinate synthase activity in overloaded skeletal muscle.

The regulation of the mitochondrial enzyme 5'-aminolevulinate synthase (ALV synthase) activity during chronic weight-bearing activity (overload) in chicken skeletal muscle was investigated. Maximal enzyme activity was increased 2.5- and 4.0-fold after 3 and 7 days of overload. The content of ALV synthase mRNA (ng/mg total RNA) was not changed after 3 days but increased (20%; P less than 0.05) after 7 days of overload. Normalizing the content of ALV synthase mRNA relative to the increase in total RNA indicated that ALV synthase mRNA increased by 1.6- and 2.0-fold at 3 and 7 days, respectively. On this basis, the increase in enzyme activity per gram protein exceeded the increase in mRNA content per gram protein by 60-70%. During overload, the activity of cytochrome oxidase was unchanged after 3 days but increased by 1.5-fold (P less than 0.05) after 7 days of overload. The data indicate that 1) the initial rise in ALV synthase mRNA and activity due to overload occurs in the absence of a prior change in the level of cytochrome oxidase, an enzyme that requires heme for its assembly, and 2) induction of ALV synthase activity is regulated largely by processes at the translational or posttranslational steps.

5-Aminolevulinate Synthetase↗

PubMed1990

Lipase regulation of muscle triglyceride hydrolysis.

The cellular control of intramuscular triglyceride (TG) metabolism involves two major identified lipases: hormone-sensitive lipase (HSL) and lipoprotein lipase (LPL). Recently, the presence of HSL in muscle has been unequivocally demonstrated. However, although it is thought that HSL is responsible for intramuscular TG lipolysis, direct evidence for this is lacking. There is evidence to suggest that HSL and LPL are simultaneously activated under a variety of conditions. The two muscle lipases appear to be turned on by the same signal and function as a coordinated unit in meeting the energy demands of muscle. At a time when HSL is presumably hydrolyzing endogenous TG, LPL is sent to the capillary beds in search of substrate. TG uptake from circulation is highly related to muscle LPL activity. Exercise training increases LPL activity in plasma and in parenchymal cells in muscle. These results suggest that training may increase the capacity to clear TG from circulation and that LPL might have a role in replenishing muscle TG stores that have been decreased with exercise.

Animals↗

PubMed1988

Neurovascular-anastomosed muscle grafts in rabbits: functional deficits result from tendon repair.

In rabbits, 9 g rectus femoris (RFM) muscles were grafted with tendon repair and with (1) nerves and blood vessels intact, (2) nerves intact and blood vessels anastomosed, or (3) nerves and blood vessels anastomosed. The influences of tendon, nerve, and vascular repair on the functional capabilities of grafts were compared 15-120 days after grafting. Data were collected on the mass, total protein content, oxidative capacity, maximum force development, and fatigability of grafts and control RFM muscles. When stabilized 90-120 days after grafting, mean values for the three types of grafts were not significantly different. Compared with values for control RFM muscles, each type of graft had significantly lower mean values for mass, total protein content, and maximum force, but the grafts were more resistant to fatigue. In RFM grafts, nerve and vascular repair do not contribute significantly to the impairments. Consequently, tendon repair appears to be responsible for the major functional deficits.

Animals↗

PubMed1985

Skeletal muscle protein synthesis and degradation in vitro: effects of temperature.

We compared the structure, function, protein synthesis, and degradation of 70- to 95-mg rat soleus muscles during 120 min of incubation at 20 and 37 degrees C. At 37 degrees C, muscles were characterized by a damaged central core region and a decline of isometric tension development during incubation. Protein synthesis in the core region at 37 degrees C was depressed relative to the peripheral region. At 20 degrees C, developed tension remained constant during incubation, and synthesis rates in the core region were not different from the peripheral region. Compared with fresh muscle, ATP concentration after incubation was not affected by temperature. After equilibration of phenylalanine specific activity between extracellular and intracellular spaces (60 min at 20 degrees C; 30 min at 37 degrees C), rates of protein synthesis at 20 [0.048 nmol tyrosine (Tyr) X mg wet mass-1 X 2 h-1] and 37 degrees C (0.160 nmol Tyr X mg wet mass-1 X 2 h-1) were linear up to 180 and 120 min, respectively. Rates of protein degradation at 20 (0.076 nmol Tyr X mg wet mass-1 X 2 h-1) and 37 degrees C (0.248 nmol Tyr X mg wet mass-1 X 2 h-1) measured after 60 min were linear up to 180 and 120 min, respectively. Incubation at 20 degrees C offers an approach to study 70- to 95-mg muscles in vitro without compromising structure and function.

Animals↗

PubMed1984

Exercise-induced adaptations of rat soleus muscle grafts.

In female Wistar rats (n = 316) under pentobarbital sodium anesthesia, the soleus muscle was autografted with its nerve reimplanted. One purpose was to characterize the chronological development of graft innervation and recruitment during locomotion. Furthermore, we tested hypotheses regarding the efficacy of run conditioning of different intensities, durations, and postgrafting initiation times to alter mass and pyruvate-malate oxidation capacity of grafts. Choline acetyltransferase activity of grafts increased from 10% of control value at 7 days postgrafting to 55 and 100% at days 28 and 56, respectively. Running-induced glycogen depletion occurred in grafts; this is consistent with graft recruitment during locomotion. There was a threshold of conditioning intensity below which no improvements occurred and above which there were improvements. Spring (50 m/min) and endurance (30 m/min) conditioning of a duration of at least 28 days that was initiated at 28 or 56 days postgrafting increased mass of grafts by 30% compared with grafts from nonconditioned rats. Easy conditioning (15 m/min) had no effect on graft mass. Changes in graft total protein content paralleled those of mass. Oxidation capacity of grafts increased significantly with some conditioning protocols, but not to the same extent as mass. The exercise-induced adaptations should improve graft function in the host organism.

Animals↗

PubMed1981

Alteration in the lactate threshold with changes in substrate availability.

The lactate threshold (LT) was studied (N=9) during ergometer cycling under control (C), high blood glucose (G), and high blood free fatty acid (F) conditions. During the G trial blood lactate (HLa) was greater than C at all work loads (P less than 0.05) Adjusted blood HLa values (HLa - pre-exercise value = delta HLa), however, were essentially the same for the C and G trials. Determination of the LT disclosed that there was no difference between the two treatments (C = 53.9 +/- 2.6% VO2 max; G=52.7 +/- 3.1% VO2max). Elevation of blood FFA levels, however, reduced both the HLa and deltaHLa at all work loads from 150-250 W (P less than 0.05) although VO2 was the same as C. In addition, a significant increase in the LT (F = 59.8 +/- 2.6% VO2max) was found for the F treatment. These data suggest that (1) the LT can be altered by substrate availability and (2) that muscle tissue anoxia may not be solely responsible for lactate production during submaximal work.

Adult↗