Stereospecificity in some central and circulatory effects of phenylisopropyl-adenosine (PIA).

The effects of l- and d-stereoisomers of phenylisopropyl-adenosine (PIA) were tested on the central nervous and circulatory system. In mice l-PIA in doses of 0.1--0.2 mg/kg i.p. reduced motor activity and muscular coordination, prolonged barbiturate sleeping time and exerted a hypothermic and analgetic effect. In most of these tests even 10--20 times higher doses of d-PIA proved to be ineffective. In isolated guinea-pig heart preparation l-PIA increased the coronary flow, diminished the contraction amplitude and frequency in approximately 1/20 of the doses than did d-PIA. Blood pressure of rats was markedly lowered by l-PIA in doses of 6--15 mug/kg i.v. but not by the same dose of d-PIA. There seems to be stereospecificity for PIA in various tissues and animals in vivo as well as in isolated organs. The l-isomer is usually 10--20 times more active than the d-form. In addition to stereospecificity at receptor sites, differences in lipid solubility of the stereoisomers could explain these findings.