Hypophysectomy and Metabolism of Brain Proteins

Abstract

Previous work (Gispen et al., 1970 a, b, 1972) indicated that removal of the pituitary markedly impaired the metabolism of RNA in the brain stem of the rat; also, fewer polysomal aggregates were present in the cells of this region. In addition, hypophysectomy caused a decrease in the incorporation of ³H-leucine into the proteins of the brain stem, measured 5 min after injection of the precursor into the diencephalon (Schotman et al., 1972a). The data led us to the hypothesis that the synthesis of proteins in the brain stem of rat is affected by hypophysectomy (Schotman et al., 1972a,b). In order to investigate whether changes in protein synthesis are indeed involved, we must first consider several questions which are crucial to the interpretation of any incorporation experiment. For instance, the size of the precursor pool should be known, since changes in the specific activity of the precursor might account for a change in the rate of incorporation (Tiplady, 1972; Dunn, 1971; Williams et al., 1949). Furthermore, the metabolism of the precursor pool seems to be of major importance; related to this is the fate of the radioactivity due originally to the precursor (Banker and Cotman, 1971; Tiplady, 1972). The experiments described below are an attempt to answer some of these questions and to assess whehter hypophysectomy interferes with protein synthesis. Preliminary evidence suggests that the metabolism of proteins is indeed affected; we therefore include data from protein analysis.