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The biological activity of guinea pig insulin was determined to be between 1 and 3 i.u. per mg when measured in vitro using isolated rat tissues and in vivo by mouse convulsion. However, when assayed by blood glucose lowering in the guinea pig, guinea pig insulin has a potency of 8.5 to 9.0 i.u. per mg. The low activity in vitro was not due to a more rapid degradation of guinea pig insulin by the rat tissues. The dose-response relationship in the isolated epididymal fat cell assay showed that guinea pig insulin had an intrinsic biological activity comparable to that of bovine insulin, but a reduced affinity for the tissue receptor sites.
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Zimmerman et al. (1974) studied this question.
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