Cardiac function and metabolism during cholinergic stimulation in the newborn lamb

Area of Science:

• Neonatal Physiology
• Cardiovascular Research
• Autonomic Nervous System Function

Background:

• The role of the autonomic nervous system in regulating cardiovascular function is critical during development.
• Cholinergic and adrenergic systems play key roles in controlling heart rate, contractility, and coronary blood flow.

Purpose of the Study:

• To investigate the impact of cholinergic stimulation on coronary flow (CF), myocardial oxygen metabolism (MVO2), and left ventricular contractility (MC) in newborn lambs.
• To determine the influence of vagal nerve stimulation on these cardiovascular parameters in the neonatal period.

Main Methods:

• Nineteen newborn lambs (1-7 days old) underwent anesthesia and surgical preparation for continuous cardiovascular monitoring.
• Measurements included coronary flow, heart rate, aortic pressure, left ventricular end-diastolic pressure, dP/dt max, and cardiac output.
• Arterial and sinus blood gases and O2 content were analyzed to calculate MVO2 and oxygen extraction.
• Acetylcholine infusion and vagal nerve stimulation were performed, with and without beta-blockade and atropine administration.

Main Results:

• Acetylcholine infusion increased left ventricular end-diastolic pressure and coronary flow (44%) but did not significantly change contractility or MVO2 per beat.
• Vagal nerve stimulation resulted in bradycardia but did not significantly alter contractility, coronary flow, oxygen extraction, or MVO2.
• These effects were abolished by atropine, confirming a cholinergic mechanism, and were not influenced by beta-blockade.

Conclusions:

• Cholinergic sensitivity is demonstrable in newborn lambs, but vagal stimulation does not significantly impact left ventricular contractility, coronary flow, or myocardial oxygen metabolism.
• The limited influence of cholinergic stimulation may be attributed to the incomplete development of the adrenergic system in the neonatal period.
• These findings highlight developmental differences in autonomic cardiovascular regulation in newborns.