Effects of hysterectomy on bone in intact rats, ovariectomized rats, and ovariectomized rats treated with estrogen

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Abstract
To determine whether the uterus plays any role in mediating the ability of estrogen to conserve bone in the rat, eight groups of animals (n = 8) with their skeletons labeled with 45Ca were studied. Rats were ovariectomized (OVX), hysterectomized (Hyst), or given sham operations (Sham) and then pair-fed a low-hydroxyproline casein diet for 4 weeks. The groups were treated orally with 17β-estradiol (E2) or vehicle, and serial measurements of biochemical markers of bone breakdown were made in weeks 1, 2, and 4. The femur density was measured by dual-energy X-ray absorptiometry (DXA), and skeletal calcium and 45Ca content were determined chemically. Final total body calcium values (mg) in the eight treatment groups were (means ± SD): Sham, 2573 ± 179; Sham + E2, 2635 ± 159; Hyst, 2537 ± 151; Hyst + E2, 2410 ± 151; OVX, 2189 ± 146; OVX + E2, 2559 ± 172; OVX/Hyst, 2138 ± 132; and OVX/Hyst + E2, 2460 ± 140. Ovariectomy raised biochemical markers of bone resorption (urinary 45Ca, hydroxyproline, and deoxypyridinoline), lowered DXA bone mineral density, and reduced total body calcium and 45Ca content in both Hyst and Sham-Hyst animals (p < 0.001), whereas E2 treatment prevented these changes. Hysterectomy did not impair the ability of E2 to conserve bone in OVX rats. Thus, we conclude that estrogen-mediated induction of growth factors from uterine tissue does not play an essential role in mediating the bone-conserving actions of estrogen in the rat. (J Bone Miner Res 1996;11:977-983)