To identify possible direct and indirect mechanisms underlying the effects
of lead on skeletal growth, 3 studies were conducted. In the first study, 1
male and 1 female pup/litter (n = 5 litters), were exposed ad libitum to 0
, 825, or 2475 ppm lead acetate in t drinking water from gestational day 4
to euthanasia on day 5 Tibial strength was tested by 3-point bending and pl
asma levels of vitamin D metabolites were measured. A dose-dependent decrea
se of the load to failure was demonstrated but only in male pups. No differ
ences in plasma levels of vitamin D metabolites were observed. In the secon
d study, conducted to test if hormone treatment would attenuate the lead de
ficits, male and female pups were exposed to 0 or 2475 ppm lead acetate and
then, from 30-60 days of age, received either saline vehicle, L-dopa, test
osterone (males only), dihydrotestosterone (DHT, males only), or estradiol
(females only). Lead exposure significantly reduced somatic growth, longitu
dinal bone growth, and bone strength during the pubertal period. Sex steroi
d replacement did not restore skeletal parameters in lead-exposed rats. L-D
opa increased plasma insulin-like growth factor 1 (IGF(1)) concentrations,
rates of bone growth, and bone strength measures in controls while having n
o effect in lead-exposed pups. The third study was conducted at 100 days of
age, when endocrine parameters have been shown to be normalized, to test f
or effects of lead exposure on bone formation during tibial limb lengthenin
g (distraction osteogenesis, DO). Both DO gap x-ray density and proximal ne
w endosteal bone formation were decreased in the distraction gaps of the le
ad-treated animals (P < 0.01). In conclusion, lead exposure reduced somatic
growth, longitudinal bone growth, and bone strength during the pubertal pe
riod, and these effects could not be reversed by a growth hormone (GH) axis
stimulator or by sex-appropriate hormones. Finally, lead exposure appears
to specifically inhibit osteoblastogenesis in vivo in adult animals.