A method for the study of the inhibition of DNA synthesis by rabbit tissue extracts

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Abstract
This paper describes a method to measure DNA synthesis in the jejunum. Everted rings of rat jejunum were incubated in the presence of [3H]thymidine. The specific activity of jejunal DNA was assayed at the end of incubation. This method was found to be valid when (1) incubation time was 30 min, (2) [3H]thymidine concentration was 90 ng/ml, and (3) paired flasks containing four, respectively, contiguous rings were compared.This method was used to investigate the existence of an intestinal chalone. An aqueous extract (S-105) of rabbit small intestine mucosa was prepared and tested for DNA synthesis inhibition in jejunum. A significant inhibition was noted, which was an hyperbolic function of the quantity of extract present in the media. The study of S-105 inhibition on other organs (kidney, liver, colon) failed to demonstrate organ specificity. However, aqueous extracts from intestinal organs were found to exert a greater inhibition than aqueous extracts from other organs. It is suggested that S-105 contains other nonspecific inhibitory fractions; our data prove the necessity of an extensive purification to demonstrate the existence of a specific chalone that regulates intestinal cell proliferation.

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