IN VITROEFFECTS OF GROWTH HORMONE AND CORTICOTROPIN PREPARATIONS ON AMINO ACID TRANSPORT BY ISOLATED RAT DIAPHRAGMS1

Abstract

Corticotropin, like growthl hormone, decreases urea formation in the adrenalectomized-nephrec-tomized rat, indicating that it has an extra-adrenal action on some phase of nitrogen metabolism. Since it was possible that this effect of corticotropin was due to an initial stimulation of amino acid tranis-port, a study was made of the in vitro effects of various corticotropin preparations on the transport of AIB-1-C14 into diaphragms of hypophysectomized rats. Purified growth hormone preparations are very active in this system. At an in vitro concentration of 1 [mu]g/ml of medium, growth hormone produced a two-fold increase in AIB-1-C14 transport, while a concentration of 100 [mu]g/ml of oxycel ACTH was necessary to evoke a comparable response. Purified cortico- ! tropins had no effect on amino acid transport. Specific chemical and immunochemical inactivation studies indicated that the ability of i oxycel ACTH to stimulate amino acid transport was due to growth '' hormone contamination. The relationship of these findings to the effect of corticotropin on urea formation is discussed.