The effect of adenyl compounds on the heart of the dogfish, Scyliorhinus canicula.

The effects of adenyl compounds were examined on dogfish atria and ventricles. Adenosine, ATP, beta, gamma-methylene ATP ( APPCP ) and 2-chloroadenosine produced negative inotropic and chronotropic effects on the dogfish atrium, which were antagonized by 8-phenyltheophylline, a P1- purinoceptor antagonist. alpha-beta-Methylene ATP ( APCPP ), which is resistant to degradation, did not produce a similar inhibitory response in the dogfish atrium. Atropine did not affect the responses to adenosine, indicating that adenosine did not produce its effects indirectly by the release of acetylcholine. The effects of adenosine and ATP were not potentiated by dipyridamole, which blocks adenosine uptake; and 2-chloroadenosine, which is reported to be resistant to uptake and deamination, was equipotent with adenosine; this suggests the absence of an adenosine uptake system. Dogfish ventricles were insensitive to adenyl compounds. Adrenaline, noradrenaline and acetylcholine produced positive inotropic effects on the ventricle. It is concluded that inhibitory P1- purinoceptors are present in the dogfish atrium. However, adenyl compounds had no direct action on the contractility of the dogfish ventricle.