Estrogen down-regulates mRNA encoding the exocytotic protein SNAP-25 in the rat pituitary gland

Exocytosis is dependent on specific proteins that are located at the secretory granule membrane, in the cytoplasm or at the plasma membrane. The mRNA expression of synaptosomal-associated protein of 25 kDa (SNAP-25) isoforms SNAP-25a and SNAP-25b, vesicle associated membrane protein (VAMP) 2, mammalian homologue of unc-18 (munc-18) and Hrs-2 was studied in the pituitary of ovariectomized rats after subcutaneous insertion of capsules containing estrogen or placebo using in situ hybridization. Estrogen treatment (0.25 mg estradiol) significantly decreased SNAP-25a (32%; 10%) and SNAP-25b (25%; 22%) mRNA levels in the anterior and intermediate lobes, respectively, whereas VAMP-2, munc-18 and Hrs-2 mRNA levels remained unchanged. The results suggest that estrogen selectively regulates SNAP-25 transcription in the pituitary gland, but leaves VAMP-2, munc-18 and Hrs-2 mRNA levels unaffected.