Activation of guinea pig pulmonary adenylate cyclase by prostacyclin.

Prostacyclin activates adenylate cyclase of guinea pig lung homogenates. The concentration for half-maximum activation was 20 nM. Kinetic analysis of the increase in enzyme activity suggested a non-cooperative, bimolecular interaction between prostacyclin and a single receptor population. Comparison of the activity of prostacyclin with that of other prostaglandins revealed a rank order of potency: prostacyclin > prostaglandin E1 > prostaglandin E2 > prostaglandin F1 alpha. 6-Oxo-prostaglandin F1 alpha, the stable hydrolysis product of prostacyclin, produced no increase in adenylate cyclase activity. Lungs were dissected before homogenisation, and prostacyclin-sensitive adenylate cyclase was identified at high concentrations in peripheral lung tissue containing small airways, blood vessels and parenchyma. The precise cellular location of these receptors remains obscure, but the probability that they are in the pulmonary vascular bed rather than airway smooth muscle is discussed.