Our long range goal is to identify the hormonal and other biochemical factors which regulate protein synthesis and degradation in heart and skeletal muscle in vivo and to assess whether the control of protein turnover is altered by ischemia or diabetes mellitus. To pursue this, we developed an 3H- phenylalanine (PHE) infusion method which, when combined with arterial and coronary sinus or femoral venous catheterization, allows quantitation of protein turnover in heart or skeletal muscle in vivo without the need for tissue biopsy. To test the validity of our proposed method we will address the following questions: a) what is the relationship between the specific activity of PHE in plasma and in muscle PHE-tRNA? b) Is there metabolism of PHE by muscle other than incorporation into protein? and c) Is there evidence for a rapidly turning over pool of PHE in muscle that might complicate use of phenylalanine as a marker for muscle protein turnover. Subsequently, we will examine the effects of insulin and circulating amino acid concentrations on the rate of protein turnover in skeletal and heart muscle in vivo. Use of the euglycemic insulin clamp technique, either alone or in combination with the infusion of a mixture of amino acids, will allow study of the effect of physiological steady state increments in plasma insulin on protein turnover. Similarly, we will examine whether changes in plasma amino acid concentration, independent of changes of plasma insulin, influences muscle protein synthesis or degradation. Similar studies will be done in dogs with insulin dependent diabetes to examine whether insulin's action to either stimulate protein synthesis or slow degradation is impaired by acute or chronic diabetes. The response of the myocardium to insulin and amino acid infusion will also be assessed in canine myocardium acutely reperfused following a myocardial infarction in order to address the question of whether such interventions can stimulate protein synthesis or slow degradation in reperfused myocardium. Abnormalities in heart protein metabolism may contribute to the diminished myocardial function (cardiomyopathy) encountered in some patients with diabetes mellitus. Furthermore, an improved understanding of both the metabolic consequences of tissue injury (myocardial infarction) and the response of injured tissue to anabolic maneuvers (insulin and amino acids) could lead to the development of new therapeutic strategies to salvage reperfused myocardium.
