EFFECT OF VASOACTIVE INTESTINAL POLYPEPTIDE (VIP) ON THE NET MOVEMENT OF ELECTROLYTES AND WATER AND GLUCOSE-ABSORPTION IN THE JEJUNAL LOOP OF SHEEP

The effect of vasoactive intestinal polypeptide (VIP) on glucose absorption and the net movement of electrolytes and water in the jejunum of sheep was investigated using a Thiry-Vella loop. Intraluminal perfusion of glucose solution (10 mM) containing NaCl (149 mM) and PEG (1 mg/ml) was done at 1 ml/min and the outflow solution was collected every ten minutes. After a 30 min control period, VIP was infused into the jugular vein for 30 min at rates of 10, 30, 100, 100 and 1,000 pmol/kg/hr. In the control period, water, sodium, chloride and glucose were absorbed, while bicarbonate and potassium were secreted. VIP decreased water absorption at 10 and 30 pmol/kg/hr and converted to secretion at over 100 pmol/kg/hr in a dose-dependent manner. Sodium flux changed to secretion only at 1,000 pmol/kg/hr, but chloride flux remained absorptive even at the highest dose. Bicarbonate secretion was stimulated dose-dependently by VIP. Potassium secretion was also increased at all doses, though this response was not dose-dependent. The net glucose absorption was not altered by VIP at any dose. Our findings indicate that VIP stimulates the jejunal secretion of water, sodium, potassium and bicarbonate and that VIP does not inhibit glucose absorption when the secretion of luminal fluid is accelerated by VIP in the jejunal loop of sheep.