Effect of adrenaline on the release of cyclic AMP by the rat diaphragm

An investigation was made of the effect of adrenaline on the tissue level and release of cyclic AMP (cAMP) into the incubation medium by the isolated rat diaphragm preparation. Adrenaline, added in vitro, caused a dose-dependent biphasic increase in the tissue level of the nucleotide. A significant elevation of the level of cAMP in the tissue was observed throughout a 60 min incubation period in the presence of 0.01, 0.1 and 10 mug/ml of adrenaline. The hormone also produced a small but significant increase in the release of cAMP into the incubation medium. The accumulation of cAMP in the incubation medium ceased after 10 min of incubation in the presence of adrenaline, although the tissu e level of the nucleotide remained considerably elevated throughout the entire incubation period. Theophylline potentiated the effect of adrenaline on both the accumulation of cAMP in the tissue and in the incubation medium. Theophylline by itself also increased the tissue level of cAMP slightly. It is concluded from the present study that the elimination of cAMP from the rat diaphragm muscle by release of the nucleotide from the cells is small.