Glucocorticoids in human, cow and rat milk.

The concentration of corticosteroids found by a competitive protein binding (CPB) assay in human milk ranged from 20 to 136 ng ml-1, in cow milk 8 to 18 ng ml-1 and rat in milk it averaged 144 ng ml-1. The lower concentration of cortisol in human milk was observed when thin layer chromatography of milk extract was made before CPB assay. Using thin layer and paper chromatography cortisone, cortisol and progesterone were identified in human milk, while in cow milk cortisol and progesterone and in rat milk only corticosterone was found. The presence of these hormones in plasma suggests a possibility of their transport from blood to the milk.