To determine whether naturally occurring fatty acids, especially saturated ones, might act directly as vasodilators, segments of human basilar arteries and umbilical arteries were precontracted submaximally with prostaglandln F^ and then exposed to different saturated fatty acids (C4 through C16) or unsaturated fatty acids (C14 1, C18:l, C18 2, and C18:3) at concentrations from 4 fiM to 4 mM. The results showed caprate (CIO) to be the most potent vasoreiaxant and basilar arteries to be more responsive (ECJO=63 /tM) than umbilical arteries (ECJO=780 fiM). Caprate also inhibited contractions elicited by KC1, serotonin, and the thromboxane analogue U46619. The relaxation was independent of the endothelium, and potency was not related to the weak capacity of caprate to inhibit Ca
T he diverse effects that saturated fatty acidshave on enzymes suggest that these acids serve physiological functions beyond that of yielding energy. These acids, for instance, uncouple phosphorylation, inhibit Na,K-ATPase, inhibit adenylate cyclase, and inhibit cytosolic guanylate cyclase but stimulate membranous guanylate cyclase. 1 -4 Moreover, each fatty acid may produce selective effects. Oleic acid more effectively inhibits Ca 2+ influx into mast cells than other Iipids and at physiological concentrations blocks 100% of an experimentally induced release of histamine.5 Among the saturated fatty acids, myristic acid was the most stimulatory of cyclic guanosine monophosphate (cGMP) production, and more so than several unsaturated ones. 3 The reasons for such stereospecificity are unknown.It is well known that the essential fatty acid arachidonate and its metabolites are vasoactive. 6 However, isolated studies suggest that other fatty acids influence vasomotion. Thus, approximately 50% of the fatty acids found in arteries are derived