Characterization of Gastric Mucosal Blood Flow Response Induced by Intragastric Capsaicin in Rats

Gastric mucosal blood flow (GMBF) was measured in the ex vivo stomachs of anesthetized rats simultaneously with mean arterial blood pressure (MBP), luminal pH and transmucosal potential difference (PD) in an attempt to characterize these responses induced by capsaicin. The stomach was mounted on a Lucite chamber, perfused with saline at the flow rate of 1 ml/min, and GMBF was measured by Laser flowmetry. Under these conditions, the pH, PD and GMBF were 3.5 to 4.0, -30 to -35 mV and 8-12 ml/min/100 g, respectively. Mucosal application of capsaicin (0.03 - 1 mg/ml for 10 min) increased GMBF in a concentration-dependent manner, without any change in PD, pH and MBP. The increased GMBF response caused by capsaicin was abolished by chemical deafferentation following systemic capsaicin injections (total dose: 100 mg/kg), significantly attenuated by pretreatment with indomethacin (5 mg/kg, s.c.) or ruthenium red (300 micrograms/kg, i.v.), but was not affected by spantide (100 micrograms/kg, i.v.), atropine (300 micrograms/kg, i.p.) or disodium cromoglycate (30 mg/kg, i.p.). In addition, when the mucosa was exposed to capsaicin repeatedly, this response showed a marked tachyphylaxis at a high concentration (6 mg/ml). These results suggest that intragastric capsaicin increased GMBF selectively through capsaicin-sensitive sensory neurons, and this action may involve endogenous prostaglandins.