INVITRO EFFECTS OF GROWTH-HORMONE ON PROTEIN-SYNTHESIS AND AMINO-ACID TRANSPORT IN THE RAT DIAPHRAGM AFTER ACUTE HYPOPHYSECTOMY

The effects of growth hormone (G H) in vitro on phenylalanine‐14C incorporation to assess protein synthesis and on a‐aminoisobutyric‐l‐3H accumulation to measure amino acid transport in the diaphragm muscle of the rat were investigated 2, 6 and 24 h after hypophysectomy or sham‐operation. In hypophysectomized animals protein synthesis was depressed. GH in vitro was without effect 2 h after hypophysectomy but stimulated protein synthesis 6 and 24 h after the operation. Six hours after hypophysectomy amino acid transport was enhanced and further stimulated by GH. After 24 h amino acid transport was depressed but was stimulated to normal levels by GH. Six hours after sham‐operation protein synthesis was depressed, but was stimulated by GH. After 24 h protein synthesis was normalized and GH was without effect. GH did not influence amino acid transport after sham‐operation. Plasma levels of GH were undetectable after hypophysectomy, markedly depressed 2 and 6 h after sham‐operation, but normal after 24 h. It is concluded that tissue responsiveness to GH develops a few hours after hypophysectomy. © 1979 Scandinavian Physiological Society