Histamine release by vagal stimulation.

Area of Science:

• Cardiovascular Physiology
• Neuropharmacology
• Autonomic Nervous System Research

Background:

• The vagus nerve plays a crucial role in regulating heart function through neurotransmitter release.
• Understanding the interplay between acetylcholine and histamine in the heart is vital for comprehending cardiac autonomic control.

Purpose of the Study:

• To investigate the release of acetylcholine and histamine from isolated guinea-pig auricles.
• To determine the effect of vagal stimulation on the release of these neurotransmitters.
• To explore the potential relationship between acetylcholine and histamine release in the cardiac system.

Main Methods:

• Isolated, vagally innervated guinea-pig auricles were used for the study.
• Measurement of acetylcholine and histamine content in the effluent.
• Vagal nerve stimulation was employed to evoke neurotransmitter release.
• Pharmacological agents (acetylcholinesterase inhibitors, atropine, eserine) were used to modulate neurotransmitter activity.

Main Results:

• Acetylcholine overflow was detected upon stimulation, but only when acetylcholinesterase was inhibited.
• Histamine overflow was measurable even without cholinesterase inhibition and increased significantly during vagal stimulation.
• Vagally evoked histamine overflow was inhibited by atropine and enhanced by eserine, suggesting a link with cholinergic pathways.
• These findings suggest acetylcholine may act as a mediator for histamine release from cardiac stores.

Conclusions:

• Vagal stimulation leads to the release of both acetylcholine and histamine from guinea-pig auricles.
• Acetylcholine appears to play a role in the release of histamine within the heart.
• The interaction between acetylcholine and histamine may be a significant factor in cardiac autonomic regulation.