To examine the ability of
tamoxifen (TAM) to conserve bone in the
estrogen-deficient ovariectomized (OVX) rat in the presence and absence of
parathyroid hormone (PTH) six groups of rats with 45Ca-labeled bones were studied for 12 weeks. Rats were OVX, parathyroidectomized (PTX), or given
sham operations and treated with TAM (10 mg/kg body wt./wk subcutaneously) or TAM-vehicle. Treatments were: group 1 =
Sham-OVX; group 2 =
Sham-OVX + TAM; group 3 = OVX; group 4 = OVX + TAM; group 5 = OVX + PTX; and group 6 = OVX + PTX + TAM. To monitor
bone resorption serial measurements of urinary
hydroxyproline and 45Ca excretion were made during the study.
Ovariectomy raised these markers of bone breakdown and caused significant
osteopenia, whereas TAM prevented
ovariectomy increasing urinary
hydroxyproline or 45Ca and conserved bone. Final total body
calcium values (TBCa) in groups 1-6, respectively, were (mg +/- SD): 3240 +/- 300; 3260 +/- 289; 2750 +/- 231; 3212 +/- 312; 2742 +/- 199; and 3387 +/- 252. Thus
ovariectomy reduced TBCa similarly in the presence and absence of the parathyroids (p < 0.001). In contrast TAM fully protected both PT-intact and PTX rats from the osteopenic effect of
ovariectomy, despite the fact that PTX rats had a lower rate of bone turnover than PT-intact rats. However, TAM-treated OVX rats had shorter femora than OVX rats given TAM-vehicle, suggesting that TAM suppresses growth of the long bones to some degree in
estrogen-deficient animals.(ABSTRACT TRUNCATED AT 250 WORDS)