Stimulation by capsaicin of duodenal HCO3(-) secretion via afferent neurons and vanilloid receptors in rats: comparison with acid-induced HCO3(-) response.
We compared the HCO3(-) secretory response to capsaicin and mucosal acidification in rat duodenums, especially the relation to vanilloid receptor type 1 (VR1). A proximal duodenal loop was perfused with saline, and the HCO3(-) secretion was measured at pH 7.0 using a pH-stat method and by adding 10 mM HCl. The secretion was stimulated by exposing the loop to capsaicin (0.03-0.3 mg/ml) or 10 mM HCl for 10 min. Indomethacin subcutaneously or ruthenium red intravenously, a nonspecific VR1 antagonist, was given 60 or 10 min, respectively, before exposure to capsaicin or acid, while L-NAME was given intravenously 3 hr before these treatments. Capsazepine, another VR1 antagonist, was coapplied to the loop for 10 min with capsaicin or acid. Luminal application of capsaicin increased the secretion of HCO3(-) in a dose-dependent manner; this effect was markedly attenuated by chemical ablation of capsaicin-sensitive afferent neurons (CSN) as well as pretreatment with ruthenium red or capsazepine, and significantly mitigated by indomethacin or L-NAME (in an L-arginine-sensitive manner). The HCO3(-) secretion was also stimulated by mucosal acidification, and this response was attenuated by both capsaicin pretreatment, indomethacin and L-NAME, but not ruthenium red or capsazepine. Mucosal application of capsaicin as well as acid increased the mucosal PGE2 content, and these effects were both significantly attenuated by indomethacin and L-NAME. These results suggest that both capsaicin and acid cause the CSN-dependent increase in duodenal HCO3(-) secretion mediated by NO and PG, yet the mode of their action differs in terms of the ruthenium red or capsazepine sensitivity. Although luminal H+ plays a modulatory role in duodenal HCO3(-) secretion, it is unlikely that the action results from the interaction of H+ with the ruthenium red- or capsazepine-sensitive site of VR1.
Kagawa
Shigeru
S
Department of Pharmacology and Experimental Therapeutics, Kyoto Pharmaceutical University Misasagi, Yamashina, Kyoto 607-8414, Japan.
Aoi
Masako
M
Kubo
Yoshiaki
Y
Kotani
Tohru
T
Takeuchi
Koji
K
D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D002211:Capsaicin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D004396:Coloring Agents / Q000494:pharmacology; D004386:Duodenum / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011955:Receptors, Drug / Q000502:physiology*; D012039:Regional Blood Flow; D012430:Ruthenium Red / Q000494:pharmacology
D001639:Bicarbonates; D004396:Coloring Agents; D004791:Enzyme Inhibitors; D011955:Receptors, Drug; D012430:Ruthenium Red; C071423:capsazepine; D002211:Capsaicin; D019331:NG-Nitroarginine Methyl Ester