Postnatal development of pyrogenic sensitivity in guinea pigs.

Area of Science:

• Physiology
• Neonatal Immunology
• Thermoregulation

Background:

• Neonates exhibit thermoregulatory abilities but struggle to develop fever in response to endotoxin.
• This inability may stem from their limited capacity for heat storage.

Purpose of the Study:

• To investigate the pyrogenicity of endotoxin in neonatal guinea pigs at different ambient temperatures.
• To determine the age at which fever responses become detectable and identify the underlying heat production mechanisms.

Main Methods:

• Unanesthetized guinea pigs (0-32 days old) were injected with Salmonella enteritidis endotoxin or sterile saline.
• Core (colonic) and subcutaneous temperatures, oxygen uptake, and shivering were continuously monitored at room and neutral temperatures.

Main Results:

• Endotoxin generally failed to induce fever in the first postnatal week.
• Febrile responses emerged after 8 days, with initial heat production from brown adipose tissue (Tbat) shifting to skeletal muscle (Tsc) by 32 days.
• Shivering was absent in younger animals but present by 32 days of age.

Conclusions:

• Pyrogenic sensitivity is not evident in the first postnatal week of guinea pigs.
• Fever responses become evocable thereafter but can be obscured by environmental temperature fluctuations.
• The primary site of endotoxin-induced heat production shifts from brown fat to skeletal muscle during the first month of life.