COMPARATIVE ACTIVITIES OF AGONISTS OF ACTIVE DUODENAL BICARBONATE SECRETION IN THE GUINEA-PIG

The comparative activity of agonists of duodenal bicarbonate secretion was studied in the anesthetized guinea pig, where the duodenal lumen was perfused with 24 mmol/l NaHCO3 to ensure active secretion of bicar bonate. Agonists were infused alone and in combination. Dibutyryl 3',5 '-cyclic adenosine monophosphate, vasoactive intestinal polypeptide (V IP) and prostaglandin E(2) (PGE(2)) were strong stimulants of bicarbon ate secretion. Theophylline, dibutyryl 3',5'-cyclic guanosine monophos phate, glucagon and prostaglandin F-2 alpha (PGF(2 alpha)) were weaker agonists, and secretin had no effect. Combinations of any two of VIP, PGE(2) and glucagon depressed bicarbonate secretion, whereas combinat ions of PGE(2) and PGF(2 alpha), VIP and PGE(2), and glucagon and PGF( 2 alpha) increased bicarbonate secretion. The data indicate that cAMP and other secondary messengers may mediate duodenal bicarbonate secret ion.