AJP - Endocrinology and Metabolism, Vol 252, Issue 2 E176-E182, Copyright © 1987 by American Physiological Society
Triiodothyronine stimulates cartilage growth and maturation by different mechanisms
W. M. Burch and J. J. Van Wyk
The mechanisms by which triiodothyronine (T3) stimulates growth and
maturation of growth-plate cartilage in vitro were studied by incubating
embryonic chick pelvic cartilages in serum-free medium in the presence and
absence of T3 for 3 days. To determine whether T3 might stimulate
production of somatomedins by the cartilage, medium from cartilage
incubated with and without T3 was assayed for somatomedin C (Sm-C) by
radioimmunoassay. No difference in Sm-C content was found. However,
cartilage incubated with T3 and increasing amounts of human Sm-C (0.5-20
ng/ml) weighed more and had greater amounts of glycosaminoglycan than
cartilage incubated in the same concentrations of Sm-C without T3,
suggesting that T3 enhances the growth effect of somatomedin. We added a
monoclonal antibody to Sm-C (anti-Sm-C) to the organ culture to determine
whether T3's stimulatory effect on cartilage growth could be blocked. The
anti-Sm-C inhibited growth of cartilage incubated in medium alone and
blocked the growth response to T3. By using alkaline phosphatase as a
biochemical marker to follow maturation, we found that T3 stimulated a 57%
increase in alkaline phosphatase activity above cartilage incubated in
medium alone and that anti-Sm-C did not inhibit T3's stimulatory effect on
alkaline phosphatase activity. We propose two different mechanisms by which
T3 affects growth-plate cartilage: T3 promotes cartilage growth primarily
through enhancing the effect of somatomedin, and T3 stimulates cartilage
maturation possibly by accelerating the normal process of cartilage
differentiation from proliferative to hypertrophic chondrocytes.
