Characterization of prostaglandin E₂ binding to isolated human adipocytes

Prostaglandin (PG) E₂ binding to fat cells and its consequent antilipolytic effect have been studied in experiments using laboratory animals, but no binding studies have yet been reported using adipocytes from humans. Consequently, we have characterized PGE₂ binding to human isolated fat cells to compare the apparent binding constant to the IC₅₀ for the antilipolytic effect of PGE₂. Our data indicate that human fat cells contain binding sites that specifically recognize prostaglandins of the E series and demonstrate stereospecific recognition of the more potent of two 15-methyl-PGE₂ analogues. There was no evidence for rapid metabolism of PGE₂ by isolated adipocytes such as occurs in lung and liver tissue. A double-reciprocal plot of binding data obtained at saturation using [³H]PGE₂ and increasing concentrations of PGE₂ indicated a single class of binding sites with an apparent binding constant (0.54 nM) that agreed well with the IC₅₀ (0.26 nM) for the antilipolytic effect of PGE₂ we observed in human fat cells. The findings from these binding and lipolysis studies are in general agreement with published observations using adipocytes from rodents and provide evidence that the conclusions reached from previous studies of laboratory animals are relevant to adipocyte physiology in humans.