Prostaglandin E2 receptor binding and action in human fat cells.

The prostaglandin E2 (PGE2) receptor in human adipocytes was identified by the use of [3H]PGE2. The receptor binding at physiological temperature and pH was specific, saturable, and slowly reversible. Half-maximal displacement for [3H]PGE2 binding occurred with 2.5 nmol/liter. Half-maximal inhibition of isoproterenol-induced lipolysis was achieved at a concentration of PGE2 of 3.8 nmol/liter and half-maximal inhibition of basal lipolysis was achieved at a concentration of PGE2 of 0.9 nmol/liter. The order of potency for prostaglandin inhibition of receptor binding and antilipolytic effect was the same, with PGE2 greater than PGF2 alpha much greater than arachidonic acid. Scatchard analysis of the binding data revealed a nonlinear plot indicating the existence of two or more binding sites with different affinities. The binding sites of high affinity had an equilibrium constant (Kd) of 2 nmol/liter and a total binding capacity of 58 fmol/10(6) adipocytes which corresponds to about 33,000 binding sites per adipocyte. The binding sites of low affinity had a Kd of 56 nmol/liter and a total binding capacity of 700 fmol/10(6) adipocytes. We conclude that [3H]PGE2 binds to receptors in isolated human adipocytes and that their antilipolytic effects are mediated by this binding.