Cyclic AMP in normal and sympathetically aneural chick hearts during development

Basal levels of cyclic adenosine monophosphate (cAMP) were measured in embryonic chick hearts at various times during development. Basal cAMP was highest on incubation day 5 and decreased throughout the remaining incubation period. Cyclic AMP could not be stimulated above basal level by intravenous in ovo administration of isoproterenol or tyramine on incubation day 5; however, there was a decrease in cAMP 2 mins after intravenous injection which was identical to the decrease in cAMP in controls injected with saline. Heart rate decreased following intravenous injection of saline on incubation day 5, but a similar decrease was not observed following intravenous isoproterenol injection. Functional sympathetic innervation of the heart does not occur until incubation day 16, and this fact is responsible for the insensitivity to tyramine stimulation on incubation day 5. Although the level of cAMP could not be stimulated above basal level on incubation day 5, beta-antagonists caused a decrease in the level of cAMP, with no decrease in heart rate. These observations indicate that the beta-receptor is coupled to adenylate cyclase on incubation day 5 but it is questionable whether adenylate cyclase is effectively coupled to heart rate. Isoproterenol and tyramine caused a significant elevation in cardiac cAMP and heart rate on incubation day 17 following intravenous in ovo injection. Hearts made sympathetically aneural by removal of premigratory neural crest responded to isoproterenol but not tyramine on incubation day 17 which demonstrates that the morphologically aneural hearts are also functionally aneural.(ABSTRACT TRUNCATED AT 250 WORDS)