Abstract
Summary
The possibility has been investigated that thyroxine is required to support the chondrogenetic effects of growth hormone in endochondral osteogenesis. Effects of these hormones have been determined in hypophy-sectomized, thyroidectomized, and hypophy-sectomized-thyroidectomized rats, being measured by the tibial epiphyseal plate widening response commonly employed in growth hormone assay. A dose of 1-thyroxine lying between 0.25 and 0.5 μg/day (a) restored vigorous endochondral osteogenesis in thyroidecto-mized rats, (b) increased their pituitary growth hormone content to normal, and (c) in hypophysectomized-thyroidectomized rats augmented the effect of a dose of growth hormone to equal that when the growth hormone dose was given alone to hypophysectomized rats.
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