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Biomedical subjects

R A Merkel

Publications and source records attributed to R A Merkel.

53 records · Page 3Linked to original sources
PubMed1983

Effect of growth hormone, testosterone and serum concentration on actin synthesis in cultured satellite cells.

Because most of the DNA in a mature muscle accumulates during postnatal life and is derived from satellite cells, cellular regulation of protein accumulation in muscle fibers originating from satellite cells is an important aspect of muscle growth control. These experiments were designed to study the modulation of a alpha-actin accumulation in satellite cell-derived myotubes by serum and two anabolic hormones commonly assumed to be involved in muscle growth regulation; growth hormone and testosterone. Satellite cells were cultured from rats ranging in age from 5 d to 1 yr. After fusion into myotubes, various levels of pig serum, 3 to 20%, were added to culture medium, and the amount of alpha-actin per myotube nucleus was determined 4 d later. The quantity increased with increasing percentages of serum in the medium. For an assessment of the extent to which serum stimulatory activity was due to growth hormone or testosterone in the serum, similar experiments were conducted with medium containing 10% pig serum plus various levels of porcine growth hormone or testosterone. Neither of these hormones stimulated actin accumulation at concentrations from 10(-9) to 10(-6) M, a range encompassing physiological levels for each hormone. These experiments do not support the premise that either growth hormone and (or) testosterone are the blood-borne agents that interact directly with muscle to stimulate protein accretion, because neither growth hormone nor testosterone acted directly on muscle cells in vitro to stimulate muscle protein accumulation.

Actins↗
PubMed1981

Growth and muscle development of feedlot cattle of different genetic backgrounds.

The effects of crossbreeding, cattle type and dietary energy level on semitendinosus muscle (ST) development, feedlot performance, daily carcass protein and fat gain and serum anabolic hormone concentrations were studied. Over 3 consecutive years, 176 feedlot steers representing four cattle types - unselected Hereford (UH), selected Hereford (SH), Angus x Hereford x Charolais (AHC) and Angus x Hereford x Holstein (AHH) - were fed either an all-corn silage (HS) or a high grain (HG) diet. Steers were slaughtered on day 1 and at the end of the feedlot trial, and ST muscles were removed rapidly. During years 2 and 3, single blood samples were obtained from steers on days 1, 29, 57, 113 and 169, and analyzed for insulin and growth hormone (GH). Steers fed HG had a higher (P less than .005) average daily gain (ADG) than steers fed HS, and cattle type had an effect (P less than .005) on ADG. Cattle type and HG affected (P less than .005) daily carcass protein and fat gain. Weight of ST muscle and total muscle RNA, DNA and protein content increased with frame size, and HS steers had heavier (P less than .05) ST muscles than the HG steers. Steers fed HG had higher (P less than .01) serum insulin concentrations than steers fed HS, but there were no consistent cattle type effects. Serum GH concentrations were not affected by cattle type or diet. Serum insulin concentrations, combined across diet and cattle types, were correlated (P less than .01) with ADG; however, serum GH, assessed on the same basis, was not related to ADG. Average daily protein and fat gain were positively related to serum insulin and were negatively related to serum GH.

Animals↗
PubMed1977

Growth and development of gastrocnemius muscle in S 5B/PL and Osborne-Mendel rats overfed during nursing.

Three techniques for overfeeding rat pups were used from birth to 24 days of age to assess their effect on growth and development in an obesity susceptible (OM) and an obesity resistant (S 5B/P1) strain of rat. These included: (1) Feeding a semi-purified high fat rather than low fat diet to the dams (alters the energy content of milk); (2) Raising pups in litters of 3 rather than 6; and (3) Force feeding of milk in lieu of any force feeding. In OM rats there was no difference in lean body mass (excludes heart, liver and kidney) (LBM) gastrocnemius muscle weights, cell number and protein content of muscle. Body weights and gastrocnemius muscle triglycerides were significantly higher in OM rats fed the high fat diet than in those fed the low fat diet. S 5B/P1 (S) rats treated in the same manner as OM, showed no significant differences in body weight, LBM, gastrocnemius muscle weight or content of DNA, protein or triglycerides. Protein and DNA for 100 g fresh gastrocnemius muscle were similar for the two strains even though the muscle was 1 1/2 times heavier in OM than in S rats. Muscle triglycerides were higher in OM than in S rats.

Animals↗
PubMed1976

The effect of testosterone on skeletal muscle development and protein synthesis in rabbits.

The effect of testosterone administration on muscle development and protein synthesis was studied with intact male rabbits. Rabbits were randomized into three experimental groups; day 0 control (G-1), day 15 control (G-2) and day 15 testosterone (G-3). Testosterone (delta4-Androsten-17beta-ol-3-one in silastic tubing) was surgically implanted into the G-3 rabbits. On day (G-1) and day 15 (G-2 and 3) of the experiment all rabbits were injected IP with 50 mu Ci-3H-leucine. Rabbits were sacrificed at intervals after the 3H-leucine injection. Right and left semitendinosus muscles, pituitary and adrenal glands, testicles and blood samples were obtained for analysis. Testosterone improved (P less than .01) gain and feed efficiency, depressed testicle weight (P less than .01), increased serum testosterone and insulin (P less than 0.01) but did not affect adrenal and pituitary weights. Muscle moisture, fat and total protein, myofibrillar, sarcoplasmic and stromal protein fractions and RNA and DNA content were not significantly affected by testosterone although G-3 semitendinosus muscle had the highest total and myofibrillar protein, RNA, and DNA content. The testosterone treated rabbits (G-3) had higher (P less than 0.05) 3H-leucine incorporation into myofibrillar protein and lower 3H-leucine incorporation into sarcoplasmic protein than the day 0 and day 15 controls.

Adrenal Glands↗