The forgotten lactogenic activity of growth hormone: important implications for rodent studies.

Studies of the effects of GH and the mechanisms of its actions frequently use rats or mice and various recombinant human GH preparations. Authors of many of these studies appear unaware of the fact that, in rodents, human GH signals through both GH and prolactin (PRL) receptors; thus, treatment with human GH is equivalent to a combined treatment with GH and PRL. GH receptors and PRL receptors are present in multiple cell types. Importantly, PRL exerts major effects on brain neuroendocrine action, female and male reproduction, metabolism, body composition, immune responses, and a host of other functions; thus, treatment of rodents with recombinant human GH could affect these important physiological parameters.