Evidence for endothelium-derived relaxing factor in cultured cells.

Intracellular cyclic GMP concentration was used as a biochemical indicator of endothelium-dependent and organonitrate-induced responses to these vasodilators in cultured porcine aortic smooth muscle and endothelial cells. Sodium nitroprusside (10(-6) M) caused a rapid increase in cyclic GMP levels in confluent smooth muscle cell cultures but not in confluent endothelial monolayers. Adenosine triphosphate (10(-4) M) and methacholine (10(-5) M), two agents that elicit endothelium-dependent relaxation in intact vessels, failed to raise cyclic GMP concentrations in muscle or endothelial cultures alone. When the cell types were grown together in mixed culture, however, treatment with adenosine triphosphate or methacholine induced an elevation in intracellular cyclic GMP levels. These findings suggest that mixed cultures of arterial smooth muscle and endothelial cells can be used to study the phenomenon of endothelium-dependent responses in arterial smooth muscle.