Gastro-protective action of lafutidine mediated by capsaicin-sensitive afferent neurons without interaction with TRPV1 and involvement of endogenous prostaglandins

Abstract

Aim: Lafutidine, a histamine H2 receptor antagonist, exhibits gastro-protective action mediated by capsaicin-sensitive afferent neurons (CSN). We compared the effect between lafutidine and capsaicin, with respect to the interaction with endogenous prostaglandins (PG), nitric oxide (NO) and the afferent neurons, including transient receptor potential vanilloid subtype 1 (TRPV1).

Methods: Male SD rats and C57BL/6 mice, both wild-type and prostacyclin IP receptor knockout animals, were used after 18 h of fasting. Gastric lesions were induced by the po administration of HCl/ethanol (60% in 150 mmol/L HCl) in a volume of 1 mL for rats or 0.3 mL for mice.

Results: Both lafutidine and capsaicin (1-10 mg/kg, po) afforded dose-dependent protection against HCl/ethanol in rats and mice. The effects were attenuated by both the ablation of CSN and pretreatment with N(G)-nitro-L-arginine methyl ester, yet only the effect of capsaicin was mitigated by prior administration of capsazepine, the TRPV1 antagonist, as well as indomethacin. Lafutidine protected the stomach against HCl/ethanol in IP receptor knockout mice, similar to wild-type animals, while capsaicin failed to afford protection in the animals lacking IP receptors. Neither of these agents affected the mucosal PGE2 or 6-keto PGF(1alpha) contents in rat stomachs. Capsaicin evoked an increase in [Ca2+]i in rat TRPV1-transfected HEK293 cells while lafutidine did not.

Conclusion: These results suggest that although both lafutidine and capsaicin exhibit gastro-protective action mediated by CSN, the mode of their effects differs regarding the dependency on endogenous PGs/IP receptors and TRPV1. It is assumed that lafutidine interacts with CSN at yet unidentified sites other than TRPV1.

Figure 1

Effects of lafutidine (A) and capsaicin (B) on HCl/ethanol-induced gastric lesions in rats. The animals were given 1 mL of HCl/ethanol (60% ethanol in 150 mmol/L HCl) po and killed 1 h later. Lafutidine (1-10 mg/kg) and capsaicin (1-10 mg/kg) were administered po 30 min before HCl/ethanol. Ablation of capsaicin-sensitive afferent neurons was achieved by consecutive s.c. injections of capsaicin (total dose of 100 mg/kg) once daily for 3 d 2 wk before the experiment. Data are presented as the mean ± SE from 4-7 rats. ^aP < 0.05, ^cP < 0.05 vs control.

Figure 2

Effect of capsazepine on the protective action of lafutidine or capsaicin against HCl/ethanol-induced gastric lesions in rats. The animals were given 1 mL of HCl/ethanol (60% ethanol in 150 mmol/L HCl) po and killed 1 h later. Lafutidine or capsaicin was given po 30 min before HCl/ethanol. Capsazepine (12.5 mg/kg) was administered po 30 min before lafutidine or capsaicin. Data are presented as the mean ± SE from 4-7 rats. ^aP < 0.05 vs control, ^cP < 0.05 vs vehicle.

Figure 3

Effects of indomethacin and L-NAME on the protective action of lafutidine or capsaicin against HCl/ethanol-induced gastric lesions in rats. The animals were given 1 mL of HCl/ ethanol (60% ethanol in 150 mmol/L HCl) po and killed 1 h later. Lafutidine (10 mg/kg) or capsaicin (10 mg/kg) was given po 30 min before HCl/ethanol. Indomethacin (5 mg/kg) or L-NAME (20 mg/kg) was administered sc 1 h before HCl/ethanol. Data are presented as the mean ± SE from 6-9 rats. ^aP < 0.05 vs control, ^cP < 0.05 vs saline.

Figure 4

Effects of lafutidine and capsaicin on mucosal PGE₂ contents in rat stomachs. The animals were given lafutidine (10 mg/kg) or capsaicin (10 mg/kg) po and killed 1 h later. Indomethacin (5 mg/kg) was administered sc 30 min before capsaicin or lafutidine. Gastric mucosal PGE₂ content was determined by EIA. Data are presented as the mean ± SE from 5 rats. ^aP < 0.05 vs control.

Figure 5

Effects of lafutidine and capsaicin on HCl/ethanol-induced gastric lesions in wild-type and IP-receptor knockout mice. The animals were given 1 mL of HCl/ethanol (60% ethanol in 150 mmol/L HCl) po and killed 1 h later. Lafutidine (10-30 mg/kg) or capsaicin (10 mg/kg) was given po 30 min before HCl/ethanol. Data are presented as the mean ± SE from 5-7 rats. ^aP < 0.05 vs control.

Figure 6

Effects of lafutidine and capsaicin on gastric mucosal 6-keto-PGF_1α levels in mice. The animals were given capsaicin (10 mg/kg) po and killed 1 h later. Indomethacin (5 mg/kg) was administered sc 30 min before capsaicin. Gastric mucosal 6-keto-PGF_1α levels were determined by EIA. Data are presented as the mean ± SE from 4-5 rats. ^aP < 0.05 vs control.

Figure 7

Changes in the intracellular concentration of Ca²⁺ in response to capsaicin and lafutidine in HEK293 cells transfected with VR1. Rat VR1 was introduced into HEK293 cells. Capsaicin (10^-8-10^-6 mol/L) or lafutidine (10^-4 mol/L) was added to the medium. Data are presented as the mean ± SE from 3 experiments. ^aP < 0.05 vs control.