N-butanol extraction of rat, pig or human serum was found to remove a potent inhibitor of in vitro embryonic chicken cartilage metabolism. This inhibitor was active at less than 1/100 of its serum concentration and therefore interfered with in vitro somatomedin assays which were run with 1 to 10% serum in the medium. The butanol extractable inhibitor (BEI) affected [3H]uridine incorporation into both RNA and an acid soluble cartilage fraction, 35SO4 incorporation into chondromucoprotein and [3H]thymidine incorporation into DNA. Studies of the solubility and thin layer chromatographic properties of BEI, revealed that the inhibitor was probably a glucocorticoid. This hypothesis was confirmed when it was found that cortisol, corticosterone and dexamethasone in concentrations as low as 2.5 × 10−10M inhibited cartilage metabolism in the same manner as BEI. (Endocrinology95: 1600, 1974)
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Eisenbarth et al. (1974) studied this question.