Oestrogens regulate pituitary alpha 2,3-sialyltransferase messenger ribonucleic acid levels in the female rat

Follicle-stimulating hormone (FSH) is synthesized by the anterior pituitary gland in multiple molecular forms. Increased acidic/sialylated FSH charge isoforms are associated with conditions characterized by a low oestrogen ou tput. In the present study, we analysed the dynamics of the changes in mRNA levels of the enzyme Gal beta 1,3[4]GlcNAc alpha 2,3-sialyltransferase (2, 3-STase) (one of the enzymes that incorporate sialic acid residues into the FSH molecule) in intact and ovariectomized rats. The anterior pituitaries of 4-day regularly cyclic adult female Wistar rats were obtained at 1000 h on the days of pro-oestrus (P), oestrus (O), dioestrus 1 (D1) and dioestrus 2 (D2), at 0200 h, 1400 h, 1800 h and 2200 h on D1, at 1800 h on day of O and at 10100 h after 7, 14, 21, 28 and 45 days of oophorectomy performed on the morning of P. Total RNA was isolated from each gland and the 2,3-STase levels were measured by Northern blot hybridization analysis employing a 3 46-base pair cDNA probe encoding for a non-conserved amino acid sequence of the catalytic domain of the enzyme. Maximal levels of the enzyme mRNA were detected at 1000 h on D1; thereafter, they progressively decreased by 60% during the ensuing 24 h, reaching the lowest concentration values (26% of t he maximally observed level on D1) at 1000 h on day of P and remaining unch anged during the morning of O. Administration of the potent oestradiol rece ptor antagonist ICI 182,780 at 1000 h on D1 completely reverted the time-de pendent decrease in 2,3-STase mRNA levels observed during the afternoon of D1, whereas oestradiol benzoate administered at 1000 h on day of O signific antly reduced the enzyme mRNA levels (to 21% of the levels detected in vehi cle-treated controls). In ovariectomized rats, the alpha 2,3-STase mRNA pro gressively increased from day 21 to day 45 post castration. Administration of oestradiol benzoate on day 28 after oophorectomy significantly reduced t he 2,3-STase mRNA levels (to 36% of the levels detected in vehicle-injected controls); ICI 182,780 partially counteracted this oestradiol-mediated eff ect. The dynamics of these changes in 2,3-STase mRNA levels partially corre lated with changes in the relative abundance of the FSH charge isoforms sep arated by preparative chromatofocusing of anterior pituitary extracts, part icularly in glands obtained during the morning of P and O. These data demon strate for the first time that pituitary 2,3-STase is a hormonally-regulate d enzyme and that the changes in transcription and/or stability of its mRNA may be involved, in part, in the post-translational processing of the FSH molecule during certain physiological conditions.