EPIDERMAL GROWTH-FACTOR AND HUMAN GROWTH-HORMONE INDUCE 2 SODIUM-DEPENDENT ARGININE TRANSPORT-SYSTEMS AFTER MASSIVE ENTERECTOMY

Background: A combination of epidermal growth factor (EGF) and human g rowth hormone (hGH) after massive enterectomy induces a 400% increase in arginine transport in the remnant distal small intestine. The kinet ic mechanism(s) responsible for enhanced arginine transport under thes e conditions is unknown. Methods: New Zealand White rabbits underwent 70% midjejunoileal resection. After a 1-week recovery period, animals received hGH (0.2 mg/kg/d IM), EGF (1.5 mu g/kg/h SC), hGH + EGF, or v ehicle (equal volume) for 7 days. Transport of tritiated arginine into brush border membrane vesicles prepared from distal remnant small int estinal mucosa was quantified in the presence and absence of a sodium gradient over a range of arginine concentrations (25 to 5000 mu mol/L) . Results: Eadie-Hofstee transformation of the kinetic data demonstrat es two sodium-dependent arginine transport systems, comprising a high- capacity, low-affinity system and a low-capacity, high-affinity system . A combination of EGF and hGH significantly upregulates both the high -capacity (685%) and low-capacity (350%) maximum transport velocity (V -max). Additionally, EGF alone significantly upregulates V-max by 200% in the low-capacity system. There were no significant changes in tran sport affinity (K-m) in either system. Conclusions: There are two quie scent sodium-dependent arginine transport systems in the distal small intestine. A combination of EGF and hGH after massive enterectomy incr ease arginine transport by V-max upregulation in both the high-capacit y/low-affinity and low-capacity/high-affinity systems.