Abstract
1. Adenosine 3',5'-(cyclic)-monophosphate (3',5'-AMP) stimulates the synthesis of progestational steroids by rabbit ovarian tissue in vitro. 2. Other adenosine phosphates fail to increase steroidogenesis. 3. The ratio of 20alpha-hydroxypregn-4-en-3-one to progesterone, the maximal response of the tissue, and the responses of separated corpora lutea and interstitial tissue produced by luteinizing hormone are closely paralleled by 3',5'-AMP. 4. In tissues maximally stimulated by luteinizing hormone, 3',5'-AMP fails to produce an additional response. 5. The addition of theophylline, an inhibitor of phosphodiesterase, potentiates the effects of 3',5'-AMP and also luteinizing hormone. 6. The results obtained suggest that 3',5'-AMP is a mediator of the action of luteinizing hormone on progestational steroid synthesis by rabbit ovarian tissue.