Oxytocin decreases colonic motility of cold water stressed rats via oxytocin receptors

Figure 1 Colonic transit increased in intragastric cold water stressed rats. Control group: the rats treated with intragastric room temperature physiological saline; Cold group: the rats treated with intragastric cold physiological saline. ^aP < 0.05 vs cold and control rats (n = 10).

Figure 2 Effects of oxytocin (0. 01-0.3 μmol/L) on colon contraction in intragastric cold water stressed rats. A: The dose-dependent contractile response to oxytocin (OT) in colonic smooth muscle strips in cold and control groups. OT was administered at the points marked by the arrows. B: Average response to OT in the colon. ^aP < 0.05 vs the data prior to OT administration. ^cP < 0.05 vs cold and control groups (n = 6).

Figure 3 Atosiban (0. 1 mmol/L) blocked oxytocin-induced colonic response in intragastric cold water stressed rats. A: Representative traces of the effect of atosiban on oxytocin (OT)-induced colonic response in the cold group. The drug was administered at the points marked by the arrows. B: Results of colonic smooth muscle strips contraction in cold group rats. ^aP < 0.05 vs the data of atosiban treatment (n = 8).

Figure 4 Tetrodotoxin (10 μmol/L) blocked oxytocin-induced colonic response in intragastric cold water stressed rats. A: Representative traces of the effect of tetrodotoxin (TTX) on oxytocin (OT)-induced colonic response in cold group. The drug was administered at the points marked by the arrows. B: Results of colonic smooth muscle strips contraction in cold group rats. ^aP < 0.05 vs data of TTX treatment (n = 6).

Figure 5 Intragastric cold water stress increased oxytocin receptor expression in colon. A: Representative Western blots. B: Densitometry analysis. C: Positive control of immunoreactivity. Oxytocin (OT) receptor antigen is expressed in the smooth muscle (arrows) of uterus. D: OT receptor immunoreactivity is expressed in myenteric plexus (arrows) of colon. ^aP < 0.05 vs control group (n = 6). OTR: Oxytocin receptors.

Figure 6 Estradiol regulated the plasma concentration of oxytocin in intragastric cold water stressed rats. A: Weight of uterus. B: The plasma concentration of oxytocin (OT) in the four groups [control, cold, ovariectomy (OVX) + cold and OVX + E₂ + cold]. Data are expressed as mean ± SD (n = 6). ^aP < 0.05 vs control group. ^cP < 0.05 vs cold group. ^eP < 0.05 vs OVX + cold group.

Figure 7 Ovariectomy decreased the oxytocin-induced inhibition of colonic contractility in intragastric cold water stressed rats. A: Representative traces of the effect of ovariectomy (OVX) on oxytocin (OT)-induced colonic response in cold group rats. The drug was administered at the points marked by the arrows. OT-induced inhibition of colonic strips decreased after the rats were ovariectomized. B: The contraction of colonic smooth muscle strips in cold group rats. ^aP < 0.05 vs the data in normal Krebs solution. ^cP < 0.05 vs cold group and OVX + cold group (n = 6).