Local injections of human or rat growth hormone or of purified human somatomedin-C stimulate unilateral tibial epiphyseal growth in hypophysectomized rats.

The growth-promoting actions of GH are thought to be mediated by somatomedin(s) (Sms), but unilateral bone growth in hypophysectomized (HX) rats given local injections of human (h) GH has been reported. Using slightly different methods, we have confirmed these results with purified hGH and have extended them to show that four daily injections directly into the tibial epiphyseal plate of 1 or 5 micrograms/day purified rat GH or recombinant DNA-derived hGH, but not of hPRL (6 micrograms/day) caused significant cartilage growth compared to that of the vehicle-injected contralateral tibia in rats that had been HX 14 days before the first injection. Thus, it is unlikely that the effects of GH are due to contaminating growth factors in the GH preparations, because the bacteria-derived preparation of hGH, which is unlikely to have such contaminants, was also active. Furthermore, we have shown that similar injections of 100 or 500 ng/day purified hSm-C caused unilateral tibial growth in rats HX 8 days, but not 14 days, before the first injection. These results demonstrate that both GH and Sm-C have direct growth-promoting effects on cartilage in vivo and are compatible with the theory that GH may act by stimulating local SM synthesis.