STUDIES ON PLASMA SOMATOMEDIN ACTIVITY IN DIFFERENT ANIMAL SPECIES

Abstract

ABSTRACT Since responses to growth hormone (GH) have a well-defined species specificity, these studies were undertaken to determine whether responses to somatomedin exhibited similar specificity. Heparinized plasma from 10 different species ranging from fish to man was accordingly assayed for somatomedin-like activity in rat, pig, monkey and human cartilage. The magnitude of 35SO4-uptake was assessed by previously described methods and the parallelity of curves compared. A stimulating effect was obtained with plasma from man, monkey, pig, horse, cow, dog, rat and possibly the turtle, whereas pigeon and fish plasma had either no effect or showed an inhibitory effect. Although some species differences with regard to slope and magnitude of response were observed, it was concluded that inter-species responses to somatomedin are far less restricted than interspecies responses to growth hormone. This suggests that unless the overall somatomedin-like activity measured in this assay can be attributed to substances which are quantitatively and/or qualitatively different in the various species, the species specificity of growth hormone exists at the level of somatomedin induction rather than in specificity of the somatomedin produced. The response of human cartilage to somatomedin from a series of other mammals opens up practical possibilities for large scale preparation of this hormone from non-human sources.