Evidence for a colon chalone.

The molecular weight fractions of 10,000-50,000 daltons prepared from "used" medium obtained during cultivation of human colon carcinoma cells (SW-48) in vitro inhibited the proliferation and DNA synthesis of these cells. Fractions exceeding 50,000 daltons were not inhibitory; those less than 10,000 daltons were cytotoxic. The inhibitory fraction did not affect either proliferation of human fibroblasts or transformation of human lymphocytes in vitro. Similar fractions from the colon mucosa of other species inhibited the proliferation of SW-48 cells, whereas extracts of dog jejunum or lung did not. This mitotic inhibition was completely reversible and could be destroyed by preincubation with trypsin. Therefore, colon cells appear to contain a cell- (but not species) specific, endogenous mitotic inhibitor or chalone.

Increased sister-chromatid exchange in bone-marrow cells of mice exposed to whole cigarette smoke.

Using defined cigarette smoke exposure conditions, BC3F1/Cum mice were exposed nose-only to two different types of whole cigarette smoke on a daily basis for 1 week and up to 46 weeks. The number of sister-chromatid exchanges (SCEs) per metaphase was determined in bone-marrow cells. Studies were scheduled so that all cytogenetic observations were made 2-3 days after the last smoke exposure. Exposure to either type of smoke on a daily basis for 1 week or up to 46 weeks resulted in a 2-fold increase in SCEs over sham-exposed control mice. In animals exposed either chronically or for 1 week to either type of smoke, the increase in SCEs persisted for at least 1 week after cessation of smoke exposure. This is the first demonstration of the induction of SCEs in laboratory animals that have been exposed to cigarette smoke in vivo.