STEROIDS CONJUGATED TO BOVINE SERUM-ALBUMIN AS TOOLS TO DEMONSTRATE SPECIFIC STEROID NEURONAL MEMBRANE-BINDING SITES

Our laboratory has pioneered the use of bovine serum albumin (BSA) lin ked to different positions of the ring structure of progesterone to in vestigate steroid-membrane interactions, The complex can be radioiodin ated to demonstrate the existence of specific membrane progesterone bi nding sites in the rat brain, Not only are these progesterone complexe s specific ligands, but they also elicit functional responses in the c entral nervous system (CNS), particularly in the corpus striatum (CS) where progesterone-BSA conjugates linked at C-3 and C-11 positions (P- 3-BSA and P-11-BSA) alter amphetamine-evoked dopamine release. In this communication we will report our current studies that use radioiodina ted progesterone-BSA conjugates (P-S-I-125-BSA, P-6-I-125-BSA, and P-1 1-I-125-BSA) and estradiol-BSA conjugates linked at C-6 position (17 b eta-E-6-I-125-BSA and 17-E-6-BSA) to demonstrate the existence of spec ific membrane binding sites for progesterone and estrogen in several r egions of the rat brain, In addition, initial studies to isolate and p urify these membrane binding sites from digitonin-solubilized P-2-memb rane fractions by affinity chromatography are reported, The data indic ate that these sites are part of a complex membrane receptor for eithe r estrogen or progesterone, the so-called membrane estrogen receptor ( mER) and the membrane progesterone receptor (mPR), respectively.