Effect of growth hormone and thyroxine on growth and chemical composition of muscle, bone and other tissues in thyroidectomized-hypophysectomized rats

Abstract

Rats were thyroidectomized-hypophysectomized at weaning and 5 weeks later treated for 36 days with either growth hormone (0.1 or 0.5 mg/day), thyroxine (2.5 µg/day), or both. Growth hormone stimulated growth of all tissues whereas thyroxine accelerated growth of only muscle and certain viscera. The growth response of some tissues to thyroxine was as pronounced as that to growth hormone. Administration of thyroxine increased the response to growth hormone of only the tissues that grew when thyroxine was given alone. Although thyroxine had no effect on the amount of bone protein in growth hormone treated and untreated rats, it had a pronounced effect on the morphology (length and maturation) of bone. The amount of collagen in muscle increased with dosage of growth hormone; thyroxine had no effect on this response. Myosin, on the other hand, increased with growth hormone dosage only in those animals also given thyroxine. Thyroxine given alone increased myosin deposition in muscle but had no effect on collagen in muscle, bone or skin.