“… adenosine and its derivatives 5'-N-ethyl-carboxamide-adenosine (NECA), (-)-N6-(R -phenyl-isopropyl)-adenosine (R-PIA), and (+)-N6-(S-…)-adenosine (S-PIA) caused dose-dependent parallel increases in both coronary flow and the coronary efflux of radioactive cAMP with a rank order of … > R-PIA > adenosine > S-PIA.”