| Objective: To investigate the effects of carbachol, histamine and 5-HT on the longitudinal muscle strips isolated from different regions of the rabbit upper gastric body, and the effects of nucleoside and nucleotides in the longitudinal muscle strips of the rabbit upper gastric body.Methods: Three longitudinal muscle strips (upper, middle and lower strips) of the upper gastric body obtained along the greater curvature in anterior surface side, and three longitudinal muscle strips (upper, middle and lower strips) obtained from the region 1 cm to the greater curvature were used in this study. A longitudinal muscle strip near the lesser curvature in anterior surface side was used as control. Responses to carbachol, histamine, 5-HT and KCl were observed in the three longitudinal muscle strips obtained along the greater curvature. The effects of ATP, ADP, UTP and adenosine on longitudinal muscle strips of the rabbit upper gastric body were investigated.Results:1 Responses of longitudinal muscle strips obtained along the greater curvature to the same agent Carbachol (0.01~30μmol?L-1), histamine (0.1~300μmol?L-1), 5-HT (0.01~30μmol?L-1) and KCl (2~75mmol?L-1) produced concentration-dependent contractile responses in the longitudinal muscle strips (upper, middle and lower strips), and the contractile responses to the four agents in upper strip were much stronger than those in middle and lower strips (P<0.05); a small contraction was produced by the four agents only at a higher concentration in lower strip.2 Responses to different agents in one longitudinal muscle strip obtained along the greater curvatureIn the upper strip, the maximal contractile response (Emax) calculated from the cumulative concentration-response curve (CCRC) for carbachol was significantly bigger than that for KCl (P<0.05), and much bigger than that for histamine or 5-HT. In the middle strip, the values of Emax calculated from CCRCs for carbachol, histamine and 5-HT were about 50%, 18% and 8% (normalized to KCl Emax). In the lower strip, the values of Emax calculated from CCRCs for carbachol and histamine were about 30% and 11% (normalized to KCl Emax). The experimental result of 5-HT was the same as that of histamine.3 Responses to different agents in the longitudinal muscle strip near the lesser curvatureCarbachol, histamine, 5-HT and KCl produced concentration-dependent contractile responses in longitudinal muscle strips near the lesser curvature, and the order of Emax amplitude was carbachol>KCl>5-HT>histamine. 4 EC50 values of the agents producing contractile responses in longitudinal muscle strips obtained from the greater curvature and lesser curvatureThe EC50 value of carbachol (0.36±0.17μmol?L-1) in longitudinal muscle strip of the lesser curvature was less than that (1.32±0.62μmol?L-1) in the upper strip of the greater curvature, but the EC50 values of histamine were the same among the 4 longitudinal muscle strips of the greater curvature (upper, middle and lower strips) and the lesser curvature (P>0.05). The experimental result of 5-HT was the same as that of histamine. At the end of each experiment, the wet weight of strip was weighed, and there was no significant difference among the several experiment groups (P>0.05).5 Responses of longitudinal muscle strips obtained from the region 1cm to the greater curvature to the same agentCarbachol, histamine, 5-HT and KCl produced contractile responses in a concentration-dependent manner in the three longitudinal muscle strips (upper, middle and lower strips). The values of Emax and EC50 calculated from CCRC for carbachol were not different among upper, middle and lower strips (P>0.05). The experimental results of histamine and 5-HT were the same as those of carbachol.6 Effects of ATP, ADP, UTP and adenosine on longitudinal muscle strips of the upper gastric bodyATP (0.1~300μmol?L-1), ADP (0.01~30μmol?L-1), UTP (0.01~30μmol?L-1) and adenosine (0.1~100μmol?L-1) produced concentration-dependent contractile responses in longitudinal muscle strips of the rabbit upper gastric body. Emax value (16.2±2.6 %, normalized to 0.3μmol?L-1 carbachol) of ADP was much weaker than that of ATP (P<0.05). There was no significant difference between Emax values of ATP and adenosine (P>0.05), and the Emax amplitude of ATP and adenosine was much weaker than that of UTP (P<0.05).7 Relaxant responses to ATP in longitudinal muscle strips of the upper gastric bodyThe contractile response to 0.1μmol?L-1 carbachol was 3.99±0.82g. In the preparations precontracted with carbachol (0.1μmol?L-1), ATP produced obviously relaxant responses in a concentration-dependent manner.Conclusion:In the rabbit upper gastric body, the upper longitudinal muscle strip of the greater curvature contains much more smooth muscle than the lower longitudinal muscle strip. In longitudinal muscle strips (upper, middle and lower strips) obtained from the greater curvature, the subtypes of functional muscarinic receptor, histamine receptor and 5-HT receptor are the same, however, the distribution density of those functional receptors is significantly different among the upper, middle and lower strips.ATP produces contractile and relaxant responses in longitudinal muscle strips of the rabbit isolated upper gastric body. ATP-induced contraction is different from that of UTP, ADP or adenosine in pharmacological profile. The contractile and relaxant responses to nucleoside and nucleotides might be mediated by several subtypes of P receptors. |
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