Phosphodiesterase isozymes involved in regulation of formula secretion in isolated mouse stomach in vitro.

(+/-)-(E)-4-Ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide] (NOR-3), a nitric-oxide (NO) donor, is known to increase HCO(3)(-) secretion in rat stomachs, intracellularly mediated by cGMP; yet, there is no information about the phosphodiesterase (PDE) isozyme involved in this process. We examined the effects of various isozyme-selective PDE inhibitors on the secretion of HCO(3)(-) in the mouse stomach in vitro and the type(s) of PDE isozymes involved in the response to NO. The gastric mucosa of DDY mice was stripped of the muscle layer and mounted on an Ussing chamber. HCO(3)(-) secretion was measured at pH 7.0 using a pH-stat method and by adding 2 mM HCl. NOR-3, 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP), and various PDE inhibitors were added to the serosal side. Vinpocetine (PDE1 inhibitor) or zaprinast (PDE5 inhibitor) was also added serosally 30 min before NOR-3 or 8-Br-cGMP. Both NOR-3 and 8-Br-cGMP stimulated HCO(3)(-) secretion in a dose-dependent manner, and the response to NOR-3 was significantly inhibited by methylene blue. Likewise, the secretion induced by NOR-3 or 8-Br-cGMP was significantly attenuated by 6-((2S,3S)-3-(4-chloro-2-methylphenylsulfonylaminomethyl)-bicyclo(2.2.2)octan-2-yl)-5Z-hexenoic acid (ONO-8711), the PGE receptor (EP)1 antagonist, as well as indomethacin and potentiated by both vinpocetine and zaprinast at doses that had no effect by themselves on the basal secretion, whereas other subtype-selective PDE inhibitors had no effect. NOR-3 increased the mucosal PGE(2) content in a methylene blue-inhibitable manner. These results suggest that NO stimulates gastric HCO(3)(-) secretion mediated intracellularly by cGMP and modified by both PDE1 and PDE5, and this response is finally mediated by endogenous PGE(2) via the activation of EP1 receptors.

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 bicarbonate. Agonists were infused alone and in combination. Dibutyryl 3',5'-cyclic adenosine monophosphate, vasoactive intestinal polypeptide (VIP) and prostaglandin E2 (PGE2) were strong stimulants of bicarbonate secretion. Theophylline, dibutyryl 3',5'-cyclic guanosine monophosphate, glucagon and prostaglandin F2 alpha (PGF2 alpha) were weaker agonists, and secretin had no effect. Combinations of any two of VIP, PGE2 and glucagon depressed bicarbonate secretion, whereas combinations of PGE2 and PGF2 alpha, VIP and PGE2, and glucagon and PGF2 alpha increased bicarbonate secretion. The data indicate that cAMP and other secondary messengers may mediate duodenal bicarbonate secretion.