During fever, the set-point temperature in the hypothalamus is elevated by pyrogens. Which mechanism raises body temperature to the new set-point?

• A Increased sweating and cutaneous vasodilation to generate heat
• B Shivering, piloerection and cutaneous vasoconstriction to increase heat production and reduce heat loss ✓
• C Direct stimulation of brown adipose tissue thermogenesis by IL-1
• D Sympathetic cholinergic activation of eccrine sweat glands

Explanation

Pyrogens (endogenous: IL-1, IL-6, TNF-α; exogenous: LPS) stimulate PGE2 synthesis in hypothalamic vascular endothelium, raising the set-point. As the new set-point exceeds current body temperature, the hypothalamus activates heat-conservation and heat-generation responses: cutaneous vasoconstriction (reducing heat loss), shivering (increasing metabolic heat production), and piloerection (reducing convective heat loss). Sweating and vasodilation occur only after body temperature has reached the new higher set-point.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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