OVARIECTOMY ENHANCES THE EXPRESSION AND NUCLEAR TRANSLOCATION OF ANNEXIN-5 IN RAT ANTERIOR-PITUITARY GONADOTROPHS

An observation of abundant annexin 5, a novel calcium and phospholipid binding protein, in gonadotrophs of the anterior pituitary gland of o variectomized rats (Kawaminami et al., 1997 tin press)) led us to inve stigate the effect of ovariectomy on the subcellular distribution and synthesis of annexin 5. Gonadotrophs, which were identified by immunoc ytochemistry with anti LH beta antiserum, dramatically increased their size three weeks after ovariectomy. These 'castration cells' were sho wn to contain abundant annexin 5 associated with the plasma membrane. nuclear envelope and nucleoplasm. True localization within the nucleus was shown by optical sectioning with a confocal microscope. Northern blot analysis showed that annexin 5 mRNA in the anterior pituitary gla nd was increased 24 h after ovariectomy. It further increased in paral lel with LH beta mRNA at three weeks and it decreased in parallel with LH beta mRNA when estradiol (250 mu g/animal per day) was given for 3 days. These results show that the expression of pituitary annexin 5 i s controlled by ovarian estradiol and imply that annexin 5 plays a phy siological role in the nucleus of activated gonadotrophs. (C) 1998 Els evier Science Ireland Ltd. All rights reserved.