Studies on the relative effects of prostaglandins, bradykinin, 5-hydroxytryptamine and histamine on the synovial microcirculation in dogs.

1 The relative effects of prostaglandins E1, E2, F1alpha, F2alpha, bradykinin, histamine and 5-hydroxytryptamine (5-HT) on the canine synovial microcirculation were investigated using the rate of clearance of radioactive xenon (133Xe) as an index of synovial perfusion. 2 All the compounds tested, except prostaglandin F1alpha, produced a vasodilator effect. The descending order of potency of the active compounds was (i) prostaglandin E1, (ii) prostaglandin E2 and bradykinin, (iii) histamine and 5-HT, (iv) prostaglandin F2alpha. The most potent compound tested, prostaglandin E1 produced an effect in nanogram amounts in each joint. 3 Prostaglandin F2alpha has been reported to have an anti-inflammatory action; however no evidence was found of antagonism of prostaglandin E1 by two dose levels of prostaglandin F2alpha. 4 Preliminary studies showed that threshold doses of prostaglandin E1 did not potentiate the vasodilator action of threshold or sub-threshold doses of bradykinin in the dog synovium.