Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Animal Science

First Advisor

Steven Nissen


The objectives of the present study were to (1) determine the mechanism of action of [beta]-agonists on muscle protein deposition in young growing lambs; and (2) directly compare existing methodologies used to study muscle protein metabolism. The [beta]-agonist L644969 was fed (1 mg/kg feed per day, 6 lambs) for 15 days. Controls received carrier alone (6 lambs). Fractional breakdown rate of muscle protein was determined by compartmental analysis of plasma 3-methylhistidine kinetics. Amino acid flux was determined by constant infusion of (4,5-[superscript]3H) -leucine, (4,5-[superscript]2H[subscript]3) -leucine, and (1-[superscript]13C) -phenylalanine. Protein synthesis in muscle and liver was measured by constant infusion of leucine and also by a (2,3,3-[superscript]3H) -phenylalanine flooding dose method. [beta]-agonist increased nitrogen balance (11.3g/d treated, 7.0g/d control, p 0.8 leu and phe). These observations suggest that the anabolic response to [beta]-agonists may result from a decrease in protein breakdown and an increase in protein synthesis; the mechanism may vary among muscle types. In 36 lambs, the constant infusion (leu) and flooding dose (phe) models were evaluated by correlation analysis and the relationship of tissue FSR to total muscle weight. Leu FSR's were correlated among organs (R =.5-.6, P <.005) whereas phe FSR's were unrelated among organs. Leu and phe FSR's within a tissue were also unrelated. These data indicate that methodological differences exist between these tissue protein synthesis models. The individual parameters of creatinine excretion, phe flux, and 3MH pool 3 were significantly (P <.05) correlated to total muscle mass (R = 0.3-0.4). Multiple regression analysis indicated that a combination of phe flux, liver and gastrocnemius FSR (phe method) gave the best overall correlation to total muscle mass (R =.71, P <.01).



Digital Repository @ Iowa State University,

Copyright Owner

Greg Allen Link



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114 pages