677Annu. Rev. Physiol. 1945.7:677-706. Downloaded from www.annualreviews.org Access provided by Yale University -Law Library on 02/03/15. For personal use only. Quick links to online content Further ANNUAL REVIEWS Annu. Rev. Physiol. 1945.7:677-706. Downloaded from www.annualreviews.org Access provided by Yale University -Law Library on 02/03/15. For personal use only. PHARMACOLOGY FUNCTIONAL GROUPINGS IN THE MOLECULES OF CARDIAC SUBSTANCES 679 Glycosides, bufagins, and bufotoxins all contain a steroid ring system with an unsaturated lactone ring on Cl7, as, for example, digitoxin (3) and gamabufagin (53, 54) shown in Formula I and Formula II, respectively.