Biological actions of free and albumin-bound arachidonic acid

¹ Department of Veterinary Science, College of Agriculture, University of Osaka Prefecture, Sakai, Osaka, Japan

Smooth-muscle-stimulating and hypotensive actions of free and albumin-bound arachidonic acid were investigated. The jejunum and ileum of both guinea pigs and rabbits were most sensitive to the acid among the isolated small intestines of these two species and rats, and exhibited a submaximal contraction at the concentration of 1.5 x 10^–7 g/ml in Tyrode's solution at 37.5 C. A dose of 3–6 µm of the acid produced a fall (40–80 mm Hg) in the rabbit's blood pressure. The dogs were quite refractory to the depressor action of the acid. Albumin-bound arachidonic acid exhibited the same activity as the free acid in regard to both smooth-muscle stimulation and hypotensive action. These results indicate that arachidonic acid could display its biological actions when the acid is released into the blood stream.