A growth hormone releaser that left stress hormones untouched

That side effect limited how such compounds could be used. A Novo Nordisk team in Denmark set out to find a secretagogue that left the stress axis alone.

In the peer-reviewed study, testing a short synthetic peptide called ipamorelin in rat pituitary cells, live rats and pigs, the researchers found it released growth hormone as effectively as older compounds. In pigs, even at doses more than 200 times higher than needed for that effect, it did not raise ACTH or cortisol above levels seen with growth hormone releasing hormone alone.

The selectivity made ipamorelin a template for a new generation of growth hormone secretagogues designed to separate the hormone's benefits from the stress response that had shadowed earlier drugs. The 1998 work was done in rats and pigs, and whether the same clean separation holds across every human condition has kept being tested since.

Growth signal without the stress signal.