Effects of temperature and oxygen availability on circulating catecholamines in the toad Bufo marinus

Area of Science:

• Comparative Physiology
• Amphibian Physiology
• Cardiovascular Regulation

Background:

• Limited understanding of amphibian catecholamine release during hypoxia.
• Adrenergic regulation of cardio-pulmonary functions in amphibians is not well understood at the organismic level.

Purpose of the Study:

• To investigate changes in plasma catecholamine concentrations in toads (Bufo marinus) under varying hypoxic conditions and temperatures.
• To determine the blood oxygen binding properties in vitro at different temperatures and pH values.

Main Methods:

• Toads were exposed to different levels of hypoxia at 15 and 25 degrees C.
• Plasma catecholamine concentrations (adrenaline and noradrenaline) were measured.
• In vitro blood oxygen binding properties (P50, Hill's n) were determined at varying pH and temperatures.

Main Results:

• Hypoxia significantly increased plasma catecholamines (adrenaline and noradrenaline) at both temperatures.
• Catecholamine release was significantly higher at 25 degrees C compared to 15 degrees C.
• Elevated noradrenaline suggested adrenal release, with an arterial oxygen threshold around 30 mmHg.
• In vitro blood oxygen binding properties correlated with in vivo data.

Conclusions:

• Hypoxia triggers a significant catecholamine release in toads, indicating a vital role in their physiological response.
• Temperature influences the magnitude of catecholamine release during hypoxia.
• These findings enhance the understanding of amphibian cardio-pulmonary adjustments to hypoxic stress.