During fever, what mechanism raises the hypothalamic set point?

• A. Fever lowers the set point due to reduced prostaglandin synthesis in the hypothalamus.
• B. Fever raises the set point due to cortisol release from the pituitary.
• C. Fever has no effect on hypothalamic set point.
• D. Fever raises the set point due to pyrogens (IL-1, IL-6, TNF-α) triggering prostaglandin E2 production in the hypothalamus.

Answer: (D)

Fever raises the hypothalamic set point through cytokine-driven production of prostaglandin E2 in the hypothalamus. When infection occurs, immune cells release endogenous pyrogens such as IL-1, IL-6, and TNF-α. These signals stimulate local enzymes that convert arachidonic acid into prostaglandin E2 in the hypothalamus, particularly in the preoptic area. PGE2 then acts on nearby receptors to raise the set point, so the body activates heat-producing and heat-conserving responses (shivering, vasoconstriction, increased metabolism) to reach the higher temperature. Once pyrogens subside and PGE2 levels fall, the set point is reset downward and heat loss mechanisms prevail. The other options don’t fit because fever does not lower the set point, and cortisol release is not the primary mechanism by which fever raises the set point; fever clearly involves a change in the hypothalamic set point.