Abstract
Gel chromatography of normal human serum exhibits a low molecular weight fraction, which significantly inhibits the action of somatomedin on porcine rib cartilage segments. This somatomedin inhibitory fraction (SmIF) has a molecular weight of about 1250 daltons, an iso-electric point between 5 to 5.5 and shows several characteristics of a peptide nature (Ped. Res. 18:101,1984). This SmIF strongly reduces both 35S-sulphate and 3H-Thymidine incorporation into costal cartilage of young pigs and rabbits and 35S-sulphate uptake by embryonic chick cartilage. This effect is dose-dependent, both in basal and in serum stimulated conditions, and is reversible. To a similar extent, SmIF decreases the conversion of 14C-glucose into 14CO2 in epididymal fat pads of young rats, with or without addition of normal serum, insulin or triiodothyronine. In conclusion, this low molecular weight SmIF does not only inhibit specifically the in vitro action of somatomedin on cartilage of several animal species, but also counteracts the insulin-like activity of normal serum and the effect of insulin and triiodothyronine on glucose metabolism of rat adipose tissue.
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