Prostacyclin binding to guinea pig pulmonary receptors

[3H] Prostacyclin bound to membranes of guinea pig lung. Specific binding was saturable, and the results revealed two receptor classes (Kd =16 nM and 258 nM). The binding capacity of the high affinity site was 105 fmol [3H]prostacyclin per mg of membrane protein, and that of the low affinity site was 1257 fmol per mg membrane protein. A comparison of selected prostaglandins as inhibitors of [3H] prostacyclin binding revealed some of the structural requriements of the ligand for occupation of the high affinity receptor.