Increase in neurokinin-1 receptor-mediated colonic motor response in a rat model of irritable bowel syndrome

Figure 2 Contractile effect of NK₁R agonist on isolated distal colonic segments, isolated colonic myocytes, and NOS inhibitor-pretreated isolated colonic segments. A: The contractile sensitivity of IBS rat colon to [Sar⁹,Met(O₂)¹¹]-SP was higher than that of normal rat colon. ^aP<0.05 vs normal by Student’s t-test with Bonferroni correction; B: Under the presence of TTX (1 μmol/L), no statistical difference was detected between groups in the [Sar⁹,Met(O₂)¹¹]-SP-induced contraction; C and D: TTX increased the [Sar⁹,Met(O₂)¹¹]-SP-induced contraction in normal rat colon but not in IBS rat colon. ^bP<0.01 vs control by Student’s t-test with Bonferroni correction (n = 12 in normal control, 9 in IBS control, 8 in TTX-normal, 7 in TTX-IBS); E and F: Photographs of myocytes in normal and IBS groups under control condition (left), and under the presence of 30 nmol/L [Sar⁹,Met(O₂)¹¹]-SP (right). Bar = 30 μm. G: Dose-response plot showing the contractile effect of [Sar⁹,Met(O₂)¹¹]-SP on the isolated colonic myocytes. The [Sar⁹,Met(O₂)¹¹]-SP-induced contraction was measured as a percent decrease in cell length (n = 7 in normal, 8 in IBS); H and I: Normal and IBS rat colonic segments were incubated with a NOS inhibitor L-NAME (0.1 mmol/L) for 10 min before the cumulative administration of [Sar⁹,Met(O₂)¹¹]-SP. ^bP<0.01 vs control by Student’s t-test (H: n = 12 in control, 7 in L-NAME. I: n = 9 in control, 6 in L-NAME).