Autacoids are biological factors that are primarily characterized by the effect they have upon smooth muscle. With respect to vascular smooth muscle, there are both vasoconstrictor and vasodilator autacoids.
Vasodilator autacoids can be released during periods of exercise. Their main effect is seen in the skin, allowing for heat loss.
The word Autacoids comes from the Greek "Autos" (self) and "Acos" (drug). These are local hormones, therefore have a paracrine effect. Some notable autacoids are: eicosanoids, angiotensin, neurotensin, NO (nitric oxide), kinins, histamine, serotonin, endothelins, etc.