The reported insulin-like activity, ILA, eluted from a cation resin column, following passage of serum, has been confirmed using the rat diaphragm bioassay. Four methods reported to convert “bound” to “free ” insulin did not increase assayable ILA.

A quantitative estimate of ILA in the untreated preparation using the rat diaphragm assay was greater than the estimate obtained using the mouse in vivo assay. It is concluded that rat diaphragm measures total ILA without prior activation. These studies fail to support the concept of “free” and “bound” insulin in human serum.

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