Which of the following statements about prostaglandins is not true?

Prostaglandins are lipid compounds that play a crucial role in various bodily functions, including the regulation of inflammation, pain, and fever. The correct answer identifies a misconception about the functions of prostaglandins.

Prostaglandins are known to have a variety of effects on blood vessels. While they can cause vasoconstriction in certain contexts, they are also capable of causing vasodilation, which is the widening of blood vessels. This dual ability to constrict and dilate blood vessels makes the statement that they can "only constrict blood vessels" inaccurate. In fact, prostaglandins can have opposite effects depending on the type of prostaglandin and the specific receptors they bind to in different tissues.

The other statements are indeed true: prostaglandins promote inflammation, which is part of the body's healing response; they are synthesized in various tissues, including the renal medulla, to regulate functions like blood flow and filtration; and they are associated with the onset of pain and fever, as they can sensitize nerve endings and act on the hypothalamus to increase body temperature. Recognizing the complex roles of prostaglandins helps in understanding their broader physiological importance and the potential implications in health and disease.