Peripheral vascular responses to hyperthermia in the rat

Area of Science:

• Physiology
• Cardiovascular Research
• Thermoregulation

Background:

• Heat stroke is a critical condition characterized by systemic hyperthermia and multi-organ failure.
• Understanding the peripheral vascular responses during heat stress is crucial for predicting and preventing heat stroke.

Purpose of the Study:

• To investigate the sequence and nature of peripheral vascular responses during the prodromal period of heat stroke.
• To determine if a loss of splanchnic vasoconstriction contributes to the development of heat stroke.

Main Methods:

• Rats were instrumented with Doppler flow probes on major arteries (superior mesenteric, iliac, renal, caudal).
• Experiments were conducted in both unanesthetized and anesthetized rats exposed to high ambient temperatures (40-46°C).
• Core and tail-skin temperatures, heart rate, and mean arterial blood pressure were continuously monitored.

Main Results:

• Elevated core temperatures (up to 44°C) were observed in both groups.
• Mean arterial blood pressure initially rose, then fell precipitously as core temperature exceeded 41.5°C.
• Superior mesenteric artery resistance increased early, then declined before the blood pressure drop, suggesting a loss of splanchnic vasoconstriction.
• Differential responses were noted in iliac and renal arteries depending on anesthesia.
• External caudal artery resistance initially fell but increased terminally.

Conclusions:

• A selective loss of compensatory splanchnic vasoconstriction may trigger the cascade of events leading to heat stroke.
• These differential vascular responses are critical in the pathophysiology of heat stroke.
• The observed vascular patterns were consistent across both unanesthetized and anesthetized animal models.