What general term describes polypeptides that influence smooth muscle and incite pain?

The correct term that describes polypeptides influencing smooth muscle and inciting pain is kinins. Kinins are a group of biologically active peptides that play a significant role in various physiological processes, including the regulation of blood pressure, inflammation, and pain. They function as potent mediators that can induce contraction of smooth muscle, contributing to pain pathways, especially in inflammatory responses.

In this context, while prostaglandins also have roles in smooth muscle contractions and the sensation of pain, they are derived from fatty acids and have broader implications in inflammation and healing but are not primarily categorized as polypeptides. Cytokines are signaling proteins involved in immune responses and inflammation but do not fit the role of influencing smooth muscle directly in the same way kinins do. Endorphins, although important for pain modulation and acting as natural pain relievers, are also not characterized as influencing smooth muscle contraction in the same manner as kinins. Therefore, kinins is the most accurate term for polypeptides that fulfill both roles of influencing smooth muscle and inciting pain.