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Epidermal growth factor and human growth hormone induce two sodium-dependent arginine transport systems after massive
P Iannoli1, J H Miller, H C Sax
1Department of Surgery, University of Rochester Medical Center, New York 14642-8410, USA.
Background:
A combination of epidermal growth factor (EGF) and human growth hormone (hGH) after massive enterectomy induces a 400% increase in arginine transport in the remnant distal small intestine. The kinetic mechanism(s) responsible for enhanced arginine transport under these 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 microg/kg/h SC), hGH + EGF, or vehicle (equal volume) for 7 days. Transport of tritiated arginine into brush border membrane vesicles prepared from distal remnant small intestinal mucosa was quantified in the presence and absence of a sodium gradient over a range of arginine concentrations (25 to 5000 micromol/L).
Results:
Eadie-Hofstee transformation of the kinetic data demonstrates 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 (Vmax). Additionally, EGF alone significantly upregulates Vmax by 200% in the low-capacity system. There were no significant changes in transport affinity (Km) in either system.
Conclusions:
There are two quiescent sodium-dependent arginine transport systems in the distal small intestine. A combination of EGF and hGH after massive enterectomy increase arginine transport by Vmax upregulation in both the high-capacity/low-affinity and low-capacity/high-affinity systems.