Humoral regulation of heart rate during digestion in pythons (Python molurus and Python regius)

Area of Science:

• Physiology
• Cardiovascular Regulation
• Comparative Biology

Background:

• Pythons exhibit significant heart rate increases during digestion.
• Postprandial tachycardia in pythons is mediated by vagal tone release and nonadrenergic, noncholinergic (NANC) factors.
• Previous research suggests NANC factors are involved in regulating python heart rate post-digestion.

Purpose of the Study:

• To identify the blood-borne NANC factor responsible for postprandial tachycardia in pythons.
• To investigate the role of histamine and mast cells in the release of this factor.
• To explore the involvement of gastrin and cholecystokinin in the postprandial cardiovascular response.

Main Methods:

• Infusion of plasma from digesting pythons into fasting snakes.
• Administration of gastrin and cholecystokinin receptor antagonist proglumide.
• Treatment with mast cell stabilizer cromolyn.
• Measurement of heart rate and blood pressure in pythons under various conditions.

Main Results:

• Plasma infusion from digesting pythons induced tachycardia in fasting snakes, confirming a blood-borne NANC factor.
• Proglumide injections did not affect heart rate or blood pressure, suggesting gastrin/cholecystokinin are not primary triggers.
• Cromolyn treatment reduced postprandial heart rate but not double-blocked heart rate, indicating histamine's role but not mast cell release as the primary stimulant.

Conclusions:

• Histamine is identified as a key mediator of postprandial tachycardia in pythons.
• The release of histamine during digestion is not stimulated by gastrin or cholecystokinin.
• Mast cell release of histamine does not appear to be the primary stimulant for postprandial tachycardia.