Acetylcholine and substance P responsiveness of intestinal smooth muscles in streptozotocin diabetic rats.

We found previously that in in vitro tube form preparations of isolated intestine of streptozotocin (STZ) diabetic rats, frequency of spontaneous intraluminal pressure waves was significantly reduced in duodenum when compared with normal controls. In order to elucidate further the diabetic intestinal disorders, we examined the frequency and amplitude of spontaneous length changes and contractile responses to acetylcholine (ACh) and substance P (sP) in isolated intestinal segments of normal and experimental diabetic rats. In comparison with normal controls, we could confirm the significantly decreased frequency of spontaneous length changes in isolated longitudinal and circular muscle preparations of diabetic duodenum (1 month after STZ injection). Furthermore, amplitude of spontaneous length changes was significantly decreased in circular muscle preparations of duodenum, jejunum, and ileum but not in colon nor in longitudinal muscle preparations. Dose-response curves revealed that both ACh and sP responses were significantly decreased in longitudinal and circular muscle preparations of diabetic duodenum, jejunum, and ileum but not in colon. Mechanisms of reduced contractility of diabetic intestinal smooth muscle in response to ACh and sP were discussed.