Influence of Irradiation or Thymidine (TdR) on the Pattern of ³H-TdR Incorporation at Each Cell Position in the Crypts of the Small Intestine of the Mouse

Summary

Using autoradiographic methods it was noted that S phase cells at the bottom of the crypts in the small intestine were the most efficient scavengers of exogenous injected thymidine. The efficiency of the incorporation of ³H-TdR (salvage pathway of DNA synthesis) by cells at the crypt base (stem cell zone) was twice as high as for the S phase cells at the top of the crypt (maturing proliferative cells). There were no such position-dependent differences in incorporation of ³H-UdR (de novo pathway of DNA synthesis). Radiation (0·75–5·0 Gy ¹³⁷Cs γ-rays) inhibited the incorporation of ³H-TdR very rapidly and this was also cell-position dependent. The cells at the bottom of the crypt were the most affected. The injection of cold thymidine before ³H-TdR changed the pattern of the incorporation of ³H-TdR along the side of the crypt in a very similar way to radiation, and the grain number was decreased predominantly in the cells at lower positions.

The possibility of the existence of a regional gradient of endogenous thymidine (reutilization from intestinal sources), and the influence of irradiation on the gradient of thymidine incorporation resulting from direct and abscopal effects of whole body exposure, are discussed.

• gut
• thymidine
• ³H-TdR/³H-UdR