Exocytotic protein components in rat pituitary gland after long-term estrogen administration

Recently, a set of proteins involved in the docking and fusion machinery of secretory organelles has been identified in anterior pituitary cells. In t his study we analyzed, by Western blotting and immunocytochemistry, the exp ression of several proteins involved in exocytosis after long-term administ ration of 17 beta-estradiol (E-2) in Fischer 344 rats. No differences were observed in the amount of synaptosomal-associated protein of 25 kDa, synapt obrevin 2, syntaxin 1, synaptotagmin I and Rab3a in total brain homogenates from treated rats after E-2 administration. In striking contrast, the leve ls of all of these exocytotic proteins, including cellubrevin, were notably decreased in pituitary glands of E-2-treated rats. In addition, no differe nces were observed in the in vitro basal and 8-Br-cAMP-induced prolactin (P RL) release between pituitary cells from control and E-2-treated rats, wher eas TRH-induced PRL release in anterior pituitary cells from E-2-treated an imals was higher than in control donors. In conclusion, this study shows th at protein components of the exocytotic machinery are specifically down-reg ulated in the pituitary gland of E-2-treated Fischer 344 rats.