Movement of Radiostrontium Through Intestinal Tract of Fed or Fasted Rats. ∗

Abstract

During a study of radiostrontium absorption in rats, a simple method was developed for determining its progress through the intestinal tract. The method should prove equally of value in studies using other radioactive substances. It is particularly useful for estimating the amount of radioisotope available for absorption in different segments of the tract at various times after oral administration.

Methods. Adult female rats of Wistar strain were given 3 μc of Sr⁸⁹Cl₂ in 0.75 ml water by stomach tube. One group had been fasted during 24 hours prior to experiment, while the other group was fed ad lib. Both groups were subsequently given water ad lib., but no food. They were killed in groups of 4 at 1/2, 1, 2, 4, 6, and 24 hours, and the intestinal tracts removed and laid out in a straight line. The radioactive material present in successive 1 cm lengths of the gut was determined using a collimated Geiger counting tube, a counting ratemeter, and graphic recorder. The gut can be counted continuously by placing it on moving paper of a kymograph with extender, fixed so that the paper is horizontal.

Results. Fig. 1 shows distribution of radiostrontium at different time intervals in representative animals from the fasted group. Fig. 2 shows similar data for the fed group. It is apparent that previous feeding increased the emptying of stomach and movement of the dose through duodenum and jejunum, but resulted in longer retention in the ileum. In the fed group, emptying of colon also occurred earlier. In all cases, distribution of the isotope was not uniform, but was concentrated in separated areas.

The method described using a radio-tracer as indicator of its progress in the gut has advantages over the bead methods of Elliott(1). Alvarez(2) and other use of inert indicators because there is no lag or separation of the tracer.