AJP - Endocrinology and Metabolism, Vol 260, Issue 5 E690-E694, Copyright © 1991 by American Physiological Society
Cortical bone maturation in young hypophysectomized rats
D. A. Martinez, A. C. Vailas and R. E. Grindeland
Biodynamics Laboratory, University of Wisconsin-Madison 53706.
Cortical bone growth and maturation were studied in young growing rats (62
days) that were hypophysectomized. After 10 days, femur bones were obtained
for morphological and biochemical analysis of the middiaphysis.
Hypophysectomy significantly decreased (42%) normal body growth
demonstrated by reductions in body weight. Bone morphology data indicate
that hypophysectomy significantly inhibits the circumferential growth of
the middiaphysis as well as region-specific thickness compared with the
control group. The effects of hypophysectomy on cortical bone mineral
composition and density were significantly greater in the hypophysectomized
rats. Bone density and total mineral density were significantly greater,
17% and 24%, respectively, in the hypophysectomized group compared with
control animals. Bone collagen maturation, measured by the amount of the
mature collagen cross-link hydroxylysylpyridinoline, in the
hypophysectomized animals was significantly greater (130%). Also, collagen
concentration and content per unit volume were significantly greater, 24%
and 70%, respectively, in the hypophysectomized group. Our findings suggest
that "normal" growth and maturation of cortical bone in rapidly growing
animals is dependent upon the modulation of pituitary hormones. These data
also suggest that an increased rate of mature collagen cross-link formation
may be modified by the turnover rate of collagen and other matrix
constituents. In addition, hormonal mechanisms associated with a
suppression of bone growth may enhance the probability of mature collagen
cross-link formation.
