Estrogen receptor in rat pancreatic islets

Abstract

The cytosol fraction of pancreatic islets of the female rat was found to contain a specifically binding protein for [ 3H]-estradiol. This protein was heat sensitive and the [ 3H]-estradiol binding was eliminated by treatment with protease and sulphydryl-blocking agents. Scatchard analysis of the cytosol binding reaction, measured by charcoal-dextran assay, indicated a single class of estradiol-binding sites having high affinity ( K d = 2.9 × 10 −8 M at 0°C). The number of binding sites was calculated to be 29.6 fmol/mg cytosol protein in whole pancreas and 170 fmol/mg cytosol protein in isolated pancreatic islets after collagenase treatment. Competition studies indicated high specificity for the binding reaction, since excess (100-fold) unlabelled estrogens, diethylstilbestrol and the antiestrogen nafoxidine, all significantly reduced the binding of [ 3H]-estradiol. On the other hand, the nonestrogenic steroids dihydrotestosterone, corticosterone and progesterone had no significant effects on [ 3H]-estradiol binding. The complex had a sedimentation coefficient of 4–5 S in sucrose density gradient centrifugation in low salt. In streptozotocin-diabetic and in 3-wk pregnant rats a significant decrease in the binding of estradiol to pancreas islet cytosol was found.