(-)-Bay K 8644 liberates a contractant factor from the endothelium of the rat aorta.

The contractile activity of (-)-Bay k 8644 was assessed in rat isolated aortic ring preparations bathed in a potassium-free medium. (-)-Bay k 8644 (0.01-3 microM) caused extracellular calcium-dependent contractile responses, which were significantly greater in tissues with, than deprived of a functional endothelium. In preparations with an endothelium, the contraction was attenuated by quinacrine (1 microM), indomethacin (10 microM) and diclofenac (0.1 microM), but not changed by nordihydroguaiaretic acid (30 microM) or dazoxiben (10 microM). Thus, in the rat aorta bathed in K(+)-free medium, (-)-Bay k 8644 can cause contractile effects, apparently due to the release of an endothelium-derived contractant factor (EDCF) which is proposed to be a cyclo-oxygenase product.