Pregnenolone binding sites in the rat olfactory bulb

High concentrations of pregnenolone and its sulfate have been found in several areas of rat and human brain and seem to be controlled by local mechanisms. In the present experiments we have demonstrated pregnenolone binding sites in the cytosolic fraction of the rat olfactory bulb. The pregnenolone binding component showed a Kd = 2.34 +/- 0.66 x 10(-7) M and Nmax = 7.25 +/- 1.20 pmol/mg protein. Pregnenolone, pregnenolone sulfate and 17OH-pregnenolone competed equally for the binding sites while other steroids were less competitive. Protease and trypsin inhibited binding by 48 and 60% respectively. Sucrose density gradient analysis showed a minor peak at 4.6 s and a major one at 3.6 s. After gel filtration chromatography the pregnenolone binding component appeared as 2 peaks corresponding to molecular weights of approximately 150 and 220 kDa. Heating at 60 degrees C increased binding by 150%. These results indicate that the olfactory bulb pregnenolone binding component is complex in nature. Rat plasma also bound pregnenolone. Plasma binding sites could be partially differentiated from those in the olfactory bulb on the basis of susceptibility to lipoprotein lipase, effect of heating and mobility during polyacrylamide gel electrophoresis.