Oscillation of cyclic AMP with the heart cycle of the canine myocardium in situ.

Oscillations of cyclic AMP with the cardiac cycle were demonstrated in the canine heart in situ. For tissue sampling an ECG(R-wave)-triggered, automatically working push-freeze-drill apparatus was employed which allowed intraventricular cryobiopsies from the left ventricular muscle of anaesthetized open-chest dogs. The nucleotide cyclic AMP oscillated with the cardiac cycle during normal working conditions, the higher cyclic AMP values occurring during systole. Cyclic GMP was assayed to be without oscillatory changes during the contraction-relaxation cycle of the heart.