Somatomedin Stimulation of Sulfate Incorporation in Porcine Costal Cartilage Discs1

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Abstract
Uniform discs punched from slices of porcine costal cartilage were used to measure somatomedin stimulation of sulfate incorporation under various experimental conditions. Basal incorporation of sulfate was relatively constant in discs from different locations along a cartilage segment and stimulation (40% normal serum compared to buffer) was comparable in discs from different positions within the cartilage slices. A simple Tris-amino acid buffer allowed greater stimulation than the more highly supplemented Ham's F-10 or Dulbecco Eagle's buffers. Porcine cartilage from younger animals was more sensitive to serum stimulation (fetal > 6–9 months old > mature). Increased disc weight was significantly correlated with decreased serum stimulation using cartilage from marketable animals (6–9 months old). A maximum dry weight of 1.8 mg/disc (1 × 2.5 mm) allowed consistently good somatomedin assays. Incorporation of sulfate by discs obtained from 6–9-month-old pigs fell with increasing incubation time. The fall was slower with incubation in serum compared to buffer, and maximum stimulation occurred at 20–30 hours. When discs from older pigs were used, incorporation of sulfate did not fall with time and there was no stimulation by serum. Mean somatomedin levels measured with this system were significantly higher in normal than in hypopituitary sera (both human and rat). Somatomedin levels rose to normal in 2 hypopituitary children treated with growth hormone, confirming the growth hormone dependence of the measured somatomedin activity. (Endocrinology94: 856, 1974)

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