Organ culture of mammary tissue from pregnant mice is normally performed in the defined but complex Medium 199 (Rivera & Bern, 1961; Stockdale, Juergens & Topper, 1966). We have recently reported the use of a much simpler medium containing only inorganic salts, amino acids and glucose (Green, Skarda & Barry, 1971). This medium allows precise studies to be made of substrate requirements of the tissue at different stages of culture. The stimulation by insulin of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities, and of DNA synthesis, was identical when mammary tissue was cultured in Medium 199 and in our simplified medium (Green et al. 1971). We report here that the simplified medium is also as satisfactory as Medium 199 for certain responses that require prolactin and hydrocortisone.
Batches of 20 explants (about 7 mg of tissue) from the mammary glands of pregnant C3H mice were cultured in 5 ml of