An Immunoelectron Microscopic Study on Localization of Fibronectin by 17-beta Estradiol Effects in Rat Tibia

Chung, Soo Tai; Choi, Il Yong; Whang, Kuhn Sung; Chung, Ho Sam

Abstract

Fibronectin(FN) is a multifunctional glycoprotein with ARG-GLY-ASP(RGD) sequences that has been known as an important constituent of extracellular matrix in bone. 17-beta estradiol, bone active hormone has been reported to stimulate the in vitro production of several extracellular matrix proteins. Though it is known that estrogen withdrawal causes a significant diminition in PTH induced FN production, the hormonal regulation of FN production in bone has not been thoroughly studied. Especially the study using immunoelectron microscopy about FN production is rare. So, the author undertook tile present study to pursue the effect of estrogen on the distribution of fibronectin in the process of bone matrix formation with immunoelectron microscopy. Four to five weeks old female Sprague-Dawley rats, weighing about 150 gm, were used as experimental animals. It was grouped as ovariectomy group, sham operation group, ovarectomy with estrogen injection group, and normal control group. Each group was sacrificed at 1 week, 3 weeks and 5 weeks postoperatively. Ovaries were removed under the pentobarbital anesthesia, and for the estrogen injection group, 0.25 mg/kg of 17-beta estradiol was injected subcutaneously after oophorectomy. Immunoelectromicroscopic findings were as follows. 1 At the one week after operation, the distributions of gold particles, show the fibronectin reaction in osteoid, are similar in the control group, sham operation group, and ovariectomy with estrogen injection group at intermediate reactions, but it is severely decreased in the ovariectomy group as a weak reaction. 2. At there weeks after operation, the distributions of gold particle are similar in the control group, sham operation group and ovariectomy with estrogen injection group as intermediate reactions, but it is also decreased in the ovariectomy group as a weak reaction. 3 At the five weeks after operation, all the groups have similar distributions of gold particles as intermediate reaction. It is suggested that the estrogen secreted in ovary, partially effects on the fibronectin formation in the matrix of developing bone, and other factors stimulate and compensate the fibronectin formation with removal of ovaries.