Bufokinin: actions and distribution in the toad cardiovascular system

Area of Science:

• Pharmacology
• Neuroscience
• Amphibian Physiology

Background:

• Bufokinin is a substance P-like neuropeptide and potent spasmogen isolated from the cane toad (Bufo marinus).
• Its physiological roles, particularly in cardiovascular regulation, remain largely uncharacterized.

Purpose of the Study:

• To investigate the effects of bufokinin on systemic blood pressure and heart rate in anesthetized toads.
• To map the distribution of bufokinin-like immunoreactivity within the toad vasculature and organs.

Main Methods:

• Intravenous administration of bufokinin to anesthetized toads to assess cardiovascular responses.
• Immunohistochemical mapping using a mouse polyclonal antibody (BK3) and the avidin-biotin method to visualize bufokinin distribution.

Main Results:

• Intravenous bufokinin induced a dose-dependent fall in systemic blood pressure, with a maximum fall of 20 mmHg and an ED50 of 2.9 pmol.
• No significant changes in heart rate were observed, and bufokinin-like immunoreactivity was detected in varicose fibers associated with various blood vessels and heart tissues.
• Bufokinin-immunoreactive fibers were present in renal arteries, aorta, sciatic artery, anterior abdominal vein, hepatic portal vein, urinary bladder, tongue, and heart ventricle.

Conclusions:

• The vasodepressor action of bufokinin and its widespread distribution in the toad vasculature suggest a role in hemodynamic regulation.
• The absence of reflex tachycardia indicates a unique cardiovascular response to bufokinin in toads, potentially related to sensory nerve function.