1+2/2011 - Společnost pro pojivové tkáně

As was mentioned in the introduction,one of the most important mechanicalstimulus for maintaining bone tissue isthe most common daily activity - walking.Nowadays, many people have sedentaryjobs and that is why they spent less hoursby walking than would be appropriate. Anexample of a person whose walking activityis around 55% of a healthy standard(1.5 hours of walking compared to 2.75h)is shown – inappropriate loading leads todecrease in bone density sometimes calleddisuse, see Fig. 1. Naturally, a possibletreatment would be in spending more timewalking (1.25h more) or similar effect canbe reached by running, which is a higherosteogenic stimuli – 30 minutes of runningevery other day will compensate for thedisuse – see Fig. 1.Hyperparathyroidism was chosenas an example of biochemical control ofbone remodelling. This disease was foundto be characterised by PTH serum levels97 pg/ml, whereas the standard value is34 pg/ml. This should lead to a significantdecrease in bone density. An example ofa person who is physically active (correctmechanical stimuli on regular dailybasis, i.e. approximately 20 000 stepsper day) but suffers from hyperparathyroidism(serum level of PTH is 97 pg/ml)is depicted on Fig. 2. We may observean expected decrease in bone density.Because mechanical loading has an osteogeniceffect even in a disease state, wemay try to increase bone density (possiblyinsufficiently) only with an increasein mechanical stimulation, 30 minuterunningper every other day was chosen.The predicted improvement is depictedin Fig. 2. The considered disease state(primary hyper-parathyriodism with PTHlevels 3 times higher than normal (97.09pg/ml)) the BMD dropped by 7–15% inthe tibia and by 15% in the lumbar vertebrae(10). The presented model estimatesa decrease in bone density by 12.8% aftersuch an increase in PTH.During menopause, a decline in estradiollevels occur. In some women, thedecrease is very dramatic (a drop bellow5 pg/ml is observed, whereas a standardserum level is 40–60 pg/ml) while in somenot (serum level remains above 20 pg/ml), see (33). Further it was observed that,together with estradiol, there is a declinein nitric oxide levels – see methods sectionand references within. An example ofa woman who is physically active (correctmechanical stimuli on regular daily basis, i.e.approximately 20 000 steps per day) but ina consequence of menopause has decreasedserum levels of estradiol and nitric oxide(as mentioned above – estradiol: 2.5 pg/ml, NO level correspond to 0.02 mg/kg perday of nitroglycerin) is depicted in Fig. 3.The presented model predicts a decreaseof in bone tissue density, which does notseem to be osteoporosis yet. This may bebecause menopause is accompanied bymore effects than these two mentioned andalso most probably because they are lessphysically active (may be caused by pain).If we combine the decrease (Fig. 3) causedby menopause alone with another decline(Fig. 1) caused by improper loading, we geta significant drop by almost in the overallbone density of the femur, which can beconsidered as osteoporotic state. One possibletreatment of bone loss connected withmenopause is treated with hormone therapy(HRT). Simulation of such a treatmentthat increased estradiol serum levels to20 pg/ml (or by 0.107 pg/ml per day ofnitroglycerin treatment which is actuallyless expensive) is given in Fig. 3. Again,POHYBOVÉ ÚSTROJÍ, ročník 18, 2011, č. 1+2 33