Previous studies implied association of osteoporosis with estrogen deficiency,
immobilization and low calcium absorption only through epidemiological studies.
There have been only a few experimental studies verifing the etiologic factors of osteoporosis in vivo condition. The author conducted an experimental study using white rats in order to find out what the endocrinological and
biochemical
changes of experimentally induced oseteoporosis are and how they behave with or against each other.
White rats, eighty five in number of 3 to 6 month old females and weighing 220±12.7gm were divided into four groups. They consisted of Group I(n=10)for control, Group II (n=25)for bilateral oophrorectomy, Group III(n=25) for bilateral
division
of sciatic nerve and hip spica cast immobilization, and Group IV(n=25)for bilateral oophphorectomy and bilateral division of sciatic nerve plus hip spica cast immobilization.
Blood samples were taken preoperatively and postopertively at six weeks to check Estradiol and Oteocalcin levels there of. And then, rats were sacrified immediately after the second sampling to retrieve femora for bone mineral density
measurement and torsional stress test.
Estradiol levels before operation were 21.4±13.3 pg/ml for Group I, 31.6±3.1 pg/ml for Group II, 25.6±4.5 pg/ml for Group III and 33.7±4.5 pg/ml for Group IV, respectively. there were no significant differences observable among the groups.
Estradiol levels at six weeks postoperativelu were 42.3±18.8 pg/ml for Group I, 5.4±2.7 pg/ml for Group II, 40.8±5 pg/ml for Group III and 6.2±2.3 pg/ml for Group IV, respectively. Apparent
reductions in Group II and IV were proved of statistical significance.
Osteocalcin levels preoperatively were 1.2±0.6 ng/ml for Group I, 1.7±0.4ng/ml for Group II, 1.5±0.1 ng/ml for Group III and 1.5±0.1 ng/ml for Group IV, respoectively. At six weeks postoperatively they were 1.6±0.1 ng/ml for Group I,
1.7±0.3
ng/ml for Group II, 1.8±0.3ng/ml for Group III and 1.2±0.1ng/ml for Group IV, respectively. The differences and changes among the groups and measurements were not of statistical signifcance.
Bone mineral contents at six weeks postoperatively were 0.248±0.03g for Group I, 0.177±0.03g for Group II, 0.226±004g for Group III and 0.092±0.01g in Group IV, respectively. Low values of Group II and IV compared to those of
Group
I
and III were of statistical significance.
Torsional strength of bones at six weeks postoperatively were 4.0±0.2 N/m for Group I, 1.5±0.1 N/m for Group II, 1.5±0.1 N/m for Group III and 1.4±0.1 N/m for Group IV, respectively. Decreases of experimental groups (II, III, IV)compared to
that
of control group (I) were of statistical significance, but differences among the experimental groups were not of significance.
From above observations, it was possible to conclude that osteporosis measurable by bone mineral content and torsional stress test was caused by oophorectomy and immobilization in vivo, the former of which was more rapid and profound
than the
latter during early phase. When both factors, i.e., oophorectomy and immobilization are exerted simultaneously, the resultant osteoporosis was found in higher degree than either factor only, but not at incremental degree as one
may
expect.
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