Purification of Growth Hormone-Releasing Factor

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Abstract
Growth hormone (GH)-releasing activity of ovine hypothalamic extracts was evaluated by an in vivo assay. The extracts were injected iv into male rats and their pituitaries were removed 30 min. later. The decrease in hypophysial GH activity in the pituitaries of these rats was estimated by the tibial epiphysial cartilage test devised by Greenspan and Li. A significant decrease in GH content was taken as evidence of GH-releasing activity. Gel filtration on Sephadex G-25 separated fractions with significant GH-releasing activity at a dose of 70-80 Mg of peptide. The active material was further purified by chromatography on carboxymethylcellulose (CMC). The GH-releasing factor (GH-RF) was eluted from the column by application of ammonium acetate buffers of increasing pH and ionic strength. The highly purified GH-RF was active at a dose of 2-4 /xg of peptide as determined by the Folin-Lowry reaction. It appears to be basic polypeptide with a molecular weight of 1800-2200 on the basis of its mobility on Sephadex.

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