Cell suspensions of normal adult rad adrenals have been prepared by trypsinization and incubated in Ham's nutrient mixture F10 containing horse serum, fetal calf serum, and lima bean trypsin ...inhibitor. In most experiments culture medium was not changed during incubation. In this system the number of cells fell to 50% after 2 days, then slowly declined to 20% after 1 month of incubation. A corticosterone (B) response was seen to as little as 5 muU of ACTH per millilitre, a concentration which is within the range found in normal rat serum. With maximal stimulation (100 mU ACTH/ml) the rate of accumulation was highest during the first 24 h then slowly decreased over the following 9 days. When in separate experiments ACTH was added after various times of incubation up to 3 weeks, there was a B response which continued for as long as 1 week after the ACTH was added; the later the time at which ACTH was added the lesser was the initial B response and the longer the lag period before a substantial response occurred. In cell suspensions in medium containing 5.0 mequiv. of K+ per litre, aldosterone content increased for approximately 24 h, then showed little or no change over the next 9 days. With increased K+ concentration, aldosterone was found in greater amounts and accumulation continued for longer periods, both without and with ACTH. This adrenal cell system appears suitable for long term study of factors affecting steroidogenesis.
