Age, Nutrition, and Bone Metabolism: Analyses of Effects Using a Short-Term In Vivo Bone Model
Age, Nutrition, and Bone Metabolism: Analyses of Effects Using a Short-Term In Vivo Bone Model
Loading...
Files
Publication or External Link
Date
1987
Authors
Sinha, Rashmi
Advisor
Soares, Jos
Citation
DRUM DOI
Abstract
The preventative effects of dietary calcium, zinc,
and vitamin D metabolites on the net loss of bone were
assessed using rats of different ages. Biochemical
changes were monitored in femurs, humeri, mandibles,
scapulas, and tibias. In addition femora were sectioned
into epiphyses-metaphyses and diaphyses to evaluate
nutritional influences on the trabecular and cortical type
bone. since measurable bone degradation due to aging and
nutritional status requires long period of time, a short-term
in vivo system was developed to simultaneously
examine bone formation and resorption. The system
consisted of subcutaneous implantation of demineralized
(DB) and mineralized (MB) bone powders. There was
evidence of bone formation and resorption in the DB and MB
implants respectively, as assessed by marker enzyme
(formation-alkaline phosphatase; resorption-acid phosphatase) activities, mineral concentrations, radioisotope
incorporation, and histological studies.
The results indicated that several different bone
samples are required to adequately predict changes
occurring in the skeletal system. The epiphysesmetaphyses
of long bone is a useful sample site examining
changes occurring in trabecular bone while the diaphysis
can assess cortical bone status. There was decreased
bone formation and resorption as assessed by alkaline and
acid phosphatase activity in the MB and DB implants in the
24 month-old rats as compared to 2 month-old rats.
Dietary calcium and zinc levels did not affect the overall
status of the bones and implants in the aged rats.
Conversely, in 2 month-old rats dietary calcium at 1.0%
stimulated bone formation in the DB implant, whereas 0.2%
calcium increased bone resorption in the MB implants.
Furthermore, 75 ng dietary 1,25-dihydroxycholecalciferol
(l,25(OH) 2 D) per day increased resorption in MB implant
and inhibited mineralization of DB implants in the young
rats. Dietary zinc at 300 ppm reduced bone calcification
in 2 month-old. The results of these studies indicated
that neither high levels of dietary calcium, nor zinc, act
as prophylaxes to counteract bone loss due to aging. The
dietary use of l,25(OH) 2 D in old animals needs to be
investigated further, since results in young animals are
contradictory with reports in older rats.