Effects of long-term replacement therapy of estrogen or compound estrogen on the deposition of beta-amyloid protein in OVX rat hippocampal formation

Objective To investigate the effects of long-term replacement therapy of estrogen or compound estrogen on the deposition of beta-amyloid protein (Aβ) in ovariectomy (OVX) rat hippocampal formation. Methods Fifty seven-month-old female Sprague-Dawley rats were randomly divided into five groups: normal control, SHAM, OVX, OVX plus 17beta-estradiol (OVX/ERT), and OVX plus compound nylestriol tablet (OVX/NL). The ovariectomy was performed in OVX, OVX/NL and OVX/ERT rats and drugs were administered orally in OVX/NL and OVX/ERT rats for 35 weeks after the ovariectomy. Then the rats in all groups were sacrificed. Immunohisto-chemistry of Aβ, cell counting and imaging system were used to determine the change of Aβ deposition levels in OVX rat hippocampal formation. Results The numbers and optical density of Aβ-positive neurons of all hippocampal subregions and dentate gyrus in OVX rats were markedly higher than those of normal control, SHAM,OVX/NL, and OVX/ERT rats( P 0.05), but there were no differences in Aβ-positive neurons among normal control, SHAM,OVX/NL and OVX/ERT rats. Conclusions Long-term estrogen deficiency results in an increase of deposition of Aβ. Replacement of estrogen or compound estrogen can equally inhibit the deposition of Aβ in hippocampal formation, which may be mainly neuroprotective mechanism of estrogen.