AJP - Endocrinology and Metabolism, Vol 257, Issue 6 E903-E908, Copyright © 1989 by American Physiological Society
Estrogens and progestogens conserve bone in rats deficient in calcitonin and parathyroid hormone
A. Goulding and E. Gold
Department of Medicine, University of Otago, Dunedin, New Zealand.
To examine the abilities of estrogens and progestogens to slow bone
resorption and conserve bone in ovariectomized rats deficient in calcitonin
(CT) or parathyroid hormone (PTH), nine groups of animals with 45Ca-labeled
bones were studied for 12 wk. Rats were thyroidectomized (TX),
parathyroidectomized (PTX), or given sham neck operations (Sham) and
treated orally with either estrogen, 300 micrograms 17 beta-estradiol.kg
body wt-1.wk-1; progestogen, 500 micrograms norethisterone acetate.kg body
wt-1.wk-1; or placebo (Plac). The TX rats had parathyroid autografts and
thyroxine replacement. In all surgical groups, estradiol (E2) and
norethindrone (Nor) slowed urinary 45Ca excretion and conserved bone (P
less than 0.001). However E2 lowered urinary hydroxyproline more than Nor.
Total body Ca values (mg +/- SD) were Sham + Plac, 3,079 +/- 201; Sham +
E2, 3,886 +/- 335; Sham + Nor, 3,567 +/- 459; TX + Plac, 3,123 +/- 159; TX
+ E2, 3,869 +/- 235; TX + Nor, 3,540 +/- 422; PTX + Sham, 3,067 +/- 249;
PTX + E2, 3,775 +/- 414; PTX + Nor, 3,635 +/- 467. Importantly, E2 and Nor
conserved bone as effectively in TX and PTX groups as in Sham rats,
although the PTX rats had slower bone resorption and lower plasma
1,25-dihydroxyvitamin D values (P less than 0.001) than groups with intact
parathyroids. We conclude that the effects of estrogens and progestogens to
slow bone resorption and conserve bone are independent of CT and PTH. These
findings appear relevant to the pathogenesis and treatment of
postmenopausal osteoporosis.
