Developmental changes in alpha adrenergic effects on canine Purkinje fiber automaticity

Area of Science:

• Cardiovascular Physiology
• Developmental Biology
• Pharmacology

Background:

• Adrenergic agonists modulate canine cardiac Purkinje fiber automaticity.
• Alpha agonists typically slow, while beta agonists increase automatic discharge rates.
• These effects are known to change with maturation and development.

Purpose of the Study:

• To investigate the effects of phenylephrine, an alpha adrenergic agonist, on automaticity in neonatal and adult canine cardiac Purkinje fibers.
• To characterize age-dependent differences in the response of Purkinje fiber automaticity to alpha adrenergic stimulation.
• To explore the role of adrenergic innervation in neonatal cardiac function.

Main Methods:

• Standard microelectrode techniques were employed to record action potentials.
• Isolated neonatal (less than 10 days) and adult canine cardiac Purkinje fibers were superfused with phenylephrine.
• Pharmacological blockers (phentolamine and propranolol) were used to identify receptor involvement.

Main Results:

• Phenylephrine decreased the rate of automatic discharge in 75% of adult and 52% of neonatal fibers, an effect blocked by phentolamine.
• A subset of both adult and neonatal fibers showed an increased rate with phenylephrine.
• This increase was blocked by propranolol in adults but not neonates, and in very young neonates, it was blocked by phentolamine, suggesting a developmental shift in adrenergic response.

Conclusions:

• Neonatal Purkinje fibers exhibit an alpha adrenergic-induced acceleration of automatic rate, a phenomenon not observed in adult fibers.
• The transition from neonatal to adult response patterns is likely influenced by the growth and development of autonomic nerves and associated receptor function.
• These findings underscore the dynamic nature of cardiac adrenergic signaling during early development.