Opiates and thermoregulation in mice. I. Agonists

Area of Science:

• Pharmacology
• Neuroscience
• Physiology

Background:

• Opiate and opioid agonists are widely used for pain management.
• Their effects on body temperature regulation are complex and not fully understood.
• Understanding these thermoregulatory effects is crucial for safe clinical use.

Purpose of the Study:

• To investigate the dose-dependent effects of various opiate and opioid agonists on mouse body temperature.
• To determine the influence of ambient environmental temperature on these thermoregulatory responses.
• To correlate the thermoregulatory potencies of these agonists with their analgesic potencies.

Main Methods:

• Rectal body temperatures of mice were monitored after administration of different opiate and opioid agonists.
• Experiments were conducted at three distinct ambient temperatures: 20°C, 25°C, and 30°C.
• A range of pure agonists from eight chemical classes were tested.

Main Results:

• At 20°C, most agonists induced hyperthermia at low doses and hypothermia at higher doses. Codeine only caused hypothermia.
• At 25°C, hypothermic effects were reduced; most drugs showed biphasic or hyperthermic responses.
• At 30°C, hyperthermia was the predominant response, with exceptions like meperidine causing hypothermia.
• A strong correlation was observed between the hypothermic potency and analgesic potency of these agonists in mice.

Conclusions:

• The thermoregulatory effects of opiate and opioid agonists are complex, dose-dependent, and significantly influenced by ambient temperature.
• These temperature modulations appear characteristic of the opiate agonist class.
• There is a notable correlation between the hypothermic effects in mice and their analgesic efficacy.