Colonic transit studies with 99mTc-rhenium sulfide colloid in live rats. A preliminary study

Abnormal colonic motility is associated with clinical relevant conditions such as irritable bowel syndrome or constipation. Accurate assessment of colonic transit in an animal model would be useful in studying these conditions and screen potential drug candidates. The aim of this study was to assess if scintigraphic analyses could reliably evaluate total and segmental colonic transit as a measure of colonic motility of a non-absorbable radiotracer in rats. Normal Lewis rats (250-300 g) were given oral technetium-99m-rhenium sulfide colloid (15-20 MBq; 0.5 mL; n=4) followed by a rinse with water for injection (1.0 mL). Rats were fed and hydrated ad libitum. After 30 min, each rat was contained inside an 'imaging' tube then placed on a g-camera collimator. Whole body 5 min static images were acquired every 30 min up to 9 h, and then finally at 25 hours. Region of interest analyses were applied to the caecum/proximal colon, sigmoidal loop and distal colon/rectum. The tracer entered into the colon at approximately 4 hours, and the rats remained static to permit 'live' imaging. At 4 hours the % whole body activity was: 51% caecum/proximal colon, 39% sigmoidal loop, 6% distal colon/rectum; at 8 hours, 30% caecum/proximal colon, 13% sigmoidal loop, 7% distal colon/rectum. In the whole colon there was < or =1% of total activity present at 25 hours, and the half clearance time was determined as 4.0 hours. These results suggest this is a reliable technique of measuring regional colonic transit as a measure of colonic motility in normal rats. This methodology might be well suited to screen potential motility effects of drug candidates.