17β-oestradiol acts as a negative modulator of insulin-induced lactotroph cell proliferation through oestrogen receptor alpha, via nitric oxide/guanylyl cyclase/cGMP

Abstract

Objectives: 17b-oestradiol interacts with growth factors to modulate lactotroph cell population. However, contribution of isoforms of the oestrogen receptor in these activities is not fully understood. In the present study, we have established participation of a and b oestrogen receptors in effects of 17b-oestradiol on lactotroph proliferation induced by insulin and shown involvement of the NO⁄sGC⁄ cGMP pathway. Materials and methods: Cell cultures were prepared from anterior pituitaries of female rats to evaluate lactotroph cell proliferation using bromodeoxyuridine (BrdUrd) detection, protein expression by western blotting and cGMP by enzyme immunoassay. Results: In serum-free conditions, 17b-oestradiol and a and b oestrogen receptor agonists (PPT and DPN) failed to increase numbers of lactotroph cells undergoing mitosis. Co-incubation of 17b-oestradiol⁄insulin and PPT⁄insulin significantly decreased lactotroph mitogenic activity promoted by insulin alone. Both ICI 182780 and NOS inhibitors (L-NMMA and L-NAME) induced reversal of the anti-proliferative effect promoted by 17b-oestradiol⁄ insulin and PPT⁄insulin. Moreover, 17b-oestradiol, PPT and insulin increased sGC a1 protein expression and inhibited b1, whereas co-incubation of 17boestradiol⁄insulin or PPT⁄insulin induced increases of the two isoforms a1 and b1. 17b-oestradiol and insulin reduced cGMP production, while 17b-oestradiol⁄insulin co-incubation increased this cyclic nucleotide. Conclusions: Our results suggest that 17b-oestradiol is capable of arresting lactotroph proliferation induced by insulin through ER a with participation of the signalling NO⁄sGC⁄ cGMP pathway