| Research Abstract |
Estrogen plays an important role in prevention of development of osteoporosis. Supplementation of estrogen to postmenopausal women attenuates loss of bone mass. However, it is not evident how estrogen plays a role in bone metabolism and how it modifies actions of other hormones and local factors in bone microenviroment. We have shown that tail-suspended rat is a suitable model for studying muscle and bone atrophy induced by unloading as well as chronic stress.
In the present investigation, we studied urinary excretion of stress related hormones during 7-day tail-suspension in three different age groups of female rats. In addition, we studied how estrogen influence muscle and bone atrophy utilizing ovariectomized and tail-suspended rats. I) The results showed that basal excretions of corticosterone (B), adrenaline (A) and noradrenaline (NA) in old rats were higher than those in young rats. The responsiveness of these hormones to stress induced by tail-suspension was different among B, A and NA.Urinary excretion of A was increased by the tail-suspension in both young rats and old rats, while increment of urinary excretion of B was lower in old rats. NA excretion did not show difference in both young and old rats. II) Wet weights of soleus and gastrocnemius muscle and of femur, and Ca and Pi contents of the femur were decreased in ovariecomized rats (Ovx). Decrease in wet weights of soleus and gastrocnemius muscle during tail-suspension was not prevented by estrogen administration (E2) to Ovx, but the bone atrophy was prevented Accordingly, urinary deoxypyridinoline excretion was significantly increased by suspension in Ovx, in contrast with no change in E2. A significant decrease of blood PTH (parathyroid hormone) was observed in Ovx, while it was not altered in E2. Therefore, it is concluded that E2 plays an important role in the maintenance of bone loss but not that of muscle.
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