Duration-dependent changes in gastrointestinal function in colon and ileum from the streptozotocin-diabetic rat

Donna Sellers, Shazia Raja and Thomas Secker, Biomedical Research Centre, Sheffield Hallam University, Sheffield, S1 1WB.

Gastrointestinal disorders, such as constipation and diarrhoea, are common complications of diabetes. However, the pathophysiological mechanisms underlying these remain unclear. Altered functioning of the GI tract has previously been shown in diabetes (Talubmook et al., 2003, Anjaneyulu & Ramarao, 2002), but reports are contradictory and it may be that regions of the GI tract are differentially affected by diabetes of different durations. The aim of the present study was to investigate the responses of ileum and colon from 4 and 8 week streptozotocin-induced diabetic rats.

Male Wistar rats (200-250g) were administered streptozotocin (65mgkg-1, i.p.) and used after 4 or 8 weeks, with weight matched controls. Strips of distal ileum and colon were mounted in tissue baths in Krebs-bicarbonate solution (in mM, 118.3 NaCl, 11.7 D-Glucose, 24.9 NaHCO3, 4.7 KCl, 1.15 MgSO4, 1.15 KH2PO4, 1.9 CaCl2, 37°C, 95%O2/5%CO2). Following equilibration, (1g tension for 60 minutes) cumulative concentration-response curves (CRCs) to carbachol (10nM-100µM), potassium chloride (KCl) (10-60mM) and isoprenaline (10nM-30µM) were recorded via UF1 force transducers linked to a Powerlab system (ADInstruments). For colon, changes in frequency (contractions/five minutes (cont/5min)) and amplitude (mg/mg tissue weight) of spontaneous contractions were recorded. LogEC 50 values (molar concentration producing half maximal response) were determined via non-linear regression of CRCs (Prism software, GraphPad). Data shown is mean±SEM of n=13-16 for all groups. Differences were determined using two-way ANOVA, P<0.05 considered significant.

In ileum from 4 week diabetic animals responses to KCl and carbachol were similar to control tissues. In contrast, in colon from 4 week diabetics the frequency of basal spontaneous contractions (12.1±2.8 vs 5.3±1.5 cont/5min P<0.05) and frequency responses to carbachol were enhanced (14.7±2.2 vs 7.9±1.9 cont/5min P<0.05). Sensitivity to carbachol was also enhanced in 4 week diabetic colon (pEC50 8.60±0.05 vs 7.57±0.12 P<0.01), although amplitude responses were similar to controls. Relaxation responses to isoprenaline were enhanced in 4 week diabetic ileum (pEC50 7.9±0.3 vs 6.3±1.1 P<0.05). In 8 week diabetic ileum responses to KCl were similar to controls. Responses to carbachol were however depressed (10.9±0.7 vs 14.8±1.2 mg/mg P<0.05), along with an increased sensitivity (pEC50 6.74±0.15 vs 6.39±0.03 P<0.05). In colon the frequency of basal spontaneous contractions was increased in 8 week diabetics compared with controls (13.1±1.7 vs 5.4±1.5 cont/5min P<0.01) and frequency responses to KCl were enhanced (29.2±3.0 vs 19.5±4.0 cont/5min P<0.05). However, amplitude responses to carbachol were depressed in 8 week diabetic colon (16.1±1.9 vs 37.3±7.9 mg/mg P<0.05), and sensitivity decreased (pEC50 7.18±0.13 vs 7.56±0.12 P<0.05) and frequency responses were not significantly different (11.9±2.8 vs 7.9±1.9 cont/5min). Responses of 8 week diabetic ileum to isoprenaline were similar to control tissues.

These results suggest that alterations in gastrointestinal function are tissue-specific and dependent upon duration in the streptozotocin-induced model of diabetes.

Anjaneyulu M & Ramarao P (2002) Methods Exp. Clin. Pharmacol 24: 71-75
Talubmook C et al. (2003) Eur. J. Pharmacol 469: 153-158