Biosynthetic human insulin (BHI) was compared to pancreatic human insulin and sperm whale insulin in terms of ability to stimulate incorporation of glucose into isolated rat adipocytes and thymidine into DNA in chick embryo fibroblasts. The human insulins were identical in their effects in both assays. Sperm whale insulin was more potent than the human insulins in stimulating glucose incorporation into rat adipocytes. All three insulins showed identical stimulation of DNA synthesis in the fibroblast assay. That action, however, is mediated via the receptor for insulin-like growth factor (IGF-I). Therefore, both human insulins were evaluated in terms of binding to the IGF-1 receptor in chick embryo fibroblasts. The two human insulins behaved identically (and agreed with previous findings for sperm whale insulin). All insulins, however, were approximately 200-fold less potent than IGF-I itself in this binding assay.

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