Evaluation of hormone effects on protein turnover in isolated perfused organs

Protein turnover and its hormonal and non-hormonal control have been studied in isolated preparations of perfused liver, heart, and skeletal muscle. These preparations permit the control of protein turnover to be studied under a variety of well-defined conditions. Advantages offered by the preparations include (1) substrates and hormones are delivered to cells by the normal capillary bed; (2) the tissues remain in a good physiological state during perfusion periods up to 3 hours as judged by oxygen consumption, perfusion pressure, cell morphology, hormone responsiveness, and maintenance of in vivo levels of high energy phosphates; and (3) sufficient amounts of tissue can be obtained for analysis of enzymatic activities and metabolites involved in protein turnover, and for preparation of ribosomal subunits and polysomes, and isolation of specific proteins. This chapter presents a discussion of problems relating to the estimation of rates of protein synthesis and degradation, the identification of rate-limiting steps in these pathways under different conditions, and the localization of the effects of hormones and other factors to specific steps in these pathways. Some of the methods that have been used in this laboratory to investigate these problems are given, but a detailed presentation is not possible within the scope of this chapter.