Cyclic AMP in normal and sympathetically aneural chick hearts during development

Area of Science:

• Developmental Biology
• Cardiovascular Physiology
• Neuropharmacology

Background:

• Basal cyclic adenosine monophosphate (cAMP) levels in embryonic chick hearts change during development.
• Sympathetic innervation is crucial for cardiac response to certain stimuli.

Purpose of the Study:

• To investigate the developmental timeline of beta-adrenergic receptor function and sympathetic innervation in embryonic chick hearts.
• To determine the relationship between cAMP levels, heart rate, and sympathetic stimulation during cardiac development.

Main Methods:

• Measurement of basal cAMP levels in embryonic chick hearts at various developmental stages.
• Intravenous in ovo administration of isoproterenol, tyramine, and saline.
• Assessment of cardiac cAMP levels and heart rate responses post-injection.
• Analysis of hearts made sympathetically aneural via neural crest removal.

Main Results:

• Basal cAMP was highest on incubation day 5, decreasing thereafter.
• On incubation day 5, hearts were insensitive to isoproterenol and tyramine stimulation, showing only a saline-like decrease in cAMP and heart rate.
• Beta-antagonists decreased cAMP on day 5 without affecting heart rate, suggesting receptor-adenylate cyclase coupling but not effective heart rate coupling.
• On incubation day 17, isoproterenol and tyramine significantly elevated cardiac cAMP and heart rate.
• Aneural hearts on day 17 responded to isoproterenol but not tyramine, confirming functional aneurality.

Conclusions:

• The beta-receptor is coupled to adenylate cyclase in embryonic chick hearts by incubation day 5, but effective coupling to heart rate is absent.
• Functional sympathetic innervation, necessary for tyramine response, is established by incubation day 16.
• Developmental studies reveal distinct timelines for beta-receptor signaling and sympathetic nerve function in the embryonic heart.