The 20,000 Da variant of human growth hormone does not bind to growth hormone receptors in human liver.

The 20,000 Da variant of human growth hormone (hGH) (20K) exhibited no specific binding to hGH receptors in human liver plasma membranes. This contrasts with the 22,000 Da form of human growth hormone (22K), which bound with high affinity to the same hepatic receptor preparation. Since the liver is considered a major target organ for the somatogenic pathway of growth hormone action, this finding implies that in humans the 20K form plays little role in that pathway. The homologous hormone-receptor system examined here yielded results that differ from heterologous receptor binding experiments in animals. The differences are likely explained by the presence in non-primate mammals of more than one type of growth hormone receptor with varied specificities. In man, the 20K form of growth hormone may have a biological role distinct from that of the main 22K form of growth hormone.