Effect of hypophysectomy on the proliferation and differentiation of rat bone marrow stromal cells

Conditions such as estrogen deficiency, skeletal unloading, and aging have all been demonstrated to have various effects on the proliferation and diff erentiation of bone marrow stroma-derived osteoprogenitor cells. Here we ha ve sought to examine the effects of pituitary hormone deficiency on the pro liferation and the differentiation of these osteoprogenitor cells using the hypophysectomized (HX) rat as a model. In the present study, we use an in vitro culture system to examine the effects of HX on the osteogenic potenti al of rat bone marrow stroma. With the intact animal as a control, we used [H-3]thymidine incorporation and cell number as indexes of proliferation. W e also measured alkaline phosphatase enzyme activity, relative levels of os teocalcin expression with RT-PCR, and osteopontin and bone sialoprotein ste ady-state levels by Northern blot to delineate the effect on differentiatio n. Our results indicate that osteoprogenitor cells exposed to a pituitary h ormone-deficient environment in vivo demonstrate an enhanced proliferative capacity and also exhibit an augmented expression of differentiation marker s when exposed to an optimal environment in vitro.