[22K and 20K growth hormone: correlation of receptor binding and the biological effect on rat adipocytes]

The 20K variant of native (22K) hGH is a full agonist for the growth promoting and lactogenic properties of the hormone in vivo, but has been reported to have reduced or no insulin-like properties. To explore whether these differences could be explained at the receptor level, we compared the binding of 22K and 20K hGH to receptors in isolated rat adipocytes, a target for the insulin-like effects of the hormone. We compared then the biological insulin-like effects of both hormones using a sensitive assay based on the stimulation of lipogenesis in isolated rat adipocytes. The 20K variant was only 3% as potent as 22K hGH for binding and bioactivity, demonstrating that rat adipocyte receptors are different from those promoting the growth effect.