Actions of growth hormone, prolactin and thyroxine on serum somatomedin-like activity and growth in hypopituitary dwarf mice.

Hypopituitary dwarf mice (Snell's strain) were found to have much reduced levels of serum somatomedin when compared with normal mice (apparently normal members of the Snell strain). Treatment with bovine growth hormone, prolactin or thyroxine induced growth in these animals; this was accompanied in each case by increased levels of serum somatomedin (primarily somatomedin C). Growth hormone had a dose-dependent growth-promoting effect, but this was not reflected in dose-dependent increases in serum somatomedin levels. These results are in accordance with the concept that somatomedin is involved in the regulation of overall somatic growth, but it seems likely that other factors are also involved.