The influence of growth hormone, somatomedins, prolactin and thyroxine on the morphology of the proximal tibial epiphysis and growth plate of Snell dwarf mice.

The effects of replacement therapy with growth hormone, somatomedins, prolactin, thyroxine and the combination of growth hormone and thyroxine on the proximal tibial epiphysis and its growth plate, have been studied in Snell dwarf mice by histometric measurements. All substances tested induce an increase of the partial tibia length, the width of the metaphysis and the number of capillaries in the metaphysis. Differences however become apparent in the epiphyseal growth plate and the development of the secondary ossification centre. Growth hormone has a clear, though smaller effect on the size of the ossification centre than thyroxine. With the combination of both hormones, intermediate values are obtained, suggesting an inhibition of hGH on thyroxine-induced osteogenesis. Roughly two groups of hormones can be distinguished: growth hormone, SM and prolactin, acting mainly on cell division as shown by an increase of the zones of proliferating and degenerating cells; and thyroxine, alone or in combination with growth hormone, acting mainly on the zone of rest cells without affecting the zones of proliferating and degenerating cells.