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Osamu Furukawa, Shoji Kawauchi, Hiroshi Mimaki, Koji Takeuchi
Med Sci Monit 2000; 6(3): BR454-459
The effect of nitric oxide (NO) on HCO3- secretion was examined in vitrousing the isolated preparation of bullfrog duodenum, in relation to cyclooxygenase (COX) isozymes andendogenous prostaglandins (PGs). The tissue was bathed in unbuffered Ringer solution gassed with 100%O2 on the mucosal side and HCO3- Ringer's solution gassed with 95% O2-5% CO2 on the serosal side. TheHCO3- secretion was measured by a pH-stat method using 10 mM HCl as the titrant to keep the mucosal pHat 7.4. NOR-3 [(+/-)-(E)-Ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamine] was used as a NO donor andadded to the serosal solution. To analyze the NOR-3 action, the effects of dibutyryl guanosine-3', 5'-cyclicmonophosphate (dbcGMP), methylene blue, indomethacin (nonselective COX-inhibitor) and NS-398 (selectiveCOX-2 inhibitor) on the HCO3- response were also examined. NOR-3 (1 x 10(-4) and 3 x 10(-4) M) causedan increase of HCO3- secretion in a dose-dependent manner, reaching the level of 2.5 times greater thanbasal values at 2 hr later. Likewise, dbcGMP (1 x 10(-3) M) also caused a significant increase of theduodenal HCO3- secretion. The HCO3- stimulatory action of NOR-3 was significantly attenuated by methyleneblue (5 x 10(-5) M) and indomethacin (1 x 10(-5) M) but not by NS-398 (1 x 10(-5) M), and indomethacinalso suppressed the HCO3- response to dbcGMP. The serosal release of PGE2 was significantly increasedby both NOR-3 and dbcGMP, and these responses were inhibited by indomethacin but not NS-398. These resultssuggest that NO increases HCO3- secretion in Bullfrog duodenum in vitro, and this action is dependenton cGMP-related COX-1 activation and mediated by PGs.