Effects of exercise and disuse on bone remodeling, bone mass, and biomechanical competence in spontaneously diabetic female rats

Diabetes is associated with low bone formation. In this study we investigat e the effect of additional or reduced mechanical loading on indices of bone formation and resorption, bone mass, and biomechanical properties in spont aneously diabetic BE rats. Female diabetic (mean age 13 weeks) and age-matc hed control rats were each allocated to three experimental groups: no-inter vention; supervised running exercise program (Ex); and unloading induced by unilateral sciatic neurectomy (USN), The study period was 8 weeks, We meas ured biochemical parameters of bone formation (plasma osteocalcin) and reso rption (urinary deoxypyridinoline [Dpd]); bone mineral density (BMD) by dua l-energy X-ray absorptiometry (DXA) at middiaphyseal and metaphyseal region s of the femur; histomorphometry of the proximal tibial metaphysis (PTM); a nd biomechanical properties of the femur (neck, diaphysis, and metaphysis) and lumbar vertebra (L-5), In nondiabetic rats, Ex did not affect parameter s of bone formation/resorption and BMD, and had little effect on biomechani cal properties. USN increased Dpd excretion, whereas there was a decreased trabecular bone formation rate (BFR) on morphometry of PTM in both paralyze d and intact limbs. Compared,vith intact limbs, paralyzed limbs of USN rats showed decreased trabecular bone volume at the PTM, and decreased BMD and biomechanical properties at the distal femoral metaphysis (DFM) and, to a l esser extent, femoral neck. Diabetic rats of the three experimental groups had low: plasma osteocalcin levels and Dpd excretion, as well as low BFR on morphometry. The BMD and biomechanical properties of both femur and L-5 we re unchanged in diabetic rats, Diabetic Ex rats, however, showed a lower ma ximum load and stress at DFM than control Ex rats. Diabetic USN rats showed no increase in Dpd excretion; their paralyzed limbs showed decreased maxim um load at DFM, but there was no significant decrease in trabecular bone vo lume at PTM or BR ID at DFM. Thus, the running exercise does not affect low bone formation in diabetic rats; however, trabecular bone loss caused by d isuse is less pronounced in diabetic rats, probably as a result of low bone resorption. (C) 2000 by Elsevier Science Inc. All rights reserved.