Hypoxia and ischaemia in buffer-perfused toad hearts

Area of Science:

• Cardiovascular Physiology
• Comparative Physiology
• Ectotherm Biology

Background:

• Previous research on ectotherm heart responses to ischemia/hypoxia used non-physiological preparations.
• This limits understanding of stress tolerance in these organisms.

Purpose of the Study:

• To investigate the effects of ischemia and hypoxia on the Bufo marinus (toad) heart under physiological conditions.
• To determine if toad hearts are stressed by ischemia or hypoxia at work levels similar to intact animals.

Main Methods:

• Utilized an in situ, buffer-perfused toad heart preparation to maintain physiological pressure and flow.
• Subjected hearts to 60 minutes of ischemia and 30 minutes of hypoxia under varying workload conditions.
• Monitored cardiac output, pressure, and heart rate parameters before, during, and after experimental challenges.

Main Results:

• Hearts recovered fully from 60 minutes of ischemia and reperfusion without functional loss.
• Hypoxia at physiological pressures caused cardiac output to cease or become intermittent, with only partial recovery (50-90%) upon reoxygenation.
• Hearts under hypoxia with reduced workload maintained cardiac output and showed an overshoot effect during reoxygenation.

Conclusions:

• Toad hearts are resilient to ischemia when demand is low.
• Hypoxia poses a significant challenge to toad cardiac function, especially under physiological workload.
• Toad hearts possess intrinsic mechanisms to reduce demand during hypoxia, but recovery from hypoxic stress is incomplete.