Effect of growth hormone on prolactin receptors and on estrogen receptors in the liver of prepubertal rats

Abstract

The regulation of both the sex-differentiated prolactin (Prl) receptor and the non-sex-differentiated estrogen receptor in rat liver was studied. In prepubertal female rats both liver Prl and estrogen receptors were found at a lower concentration compared to the receptor level present in adult female rats. The effect of growth hormone (GH) treatment on Prl and estrogen receptor levels was investigated. In prepubertal female rats (17 and 22 days old), infusion of human GH using an infusion rate of 0.1 μg/h per g body weight (BW) over a period of 6 days resulted in an increase in the number of Prl receptors to a level normally found in adult female rats. Human GH also induced Prl receptors in prepubertal male rats to an adult female level. In contrast, the same infusion rate of human GH given to female rats at 17 and 22 days of age did not increase the level of estrogen receptor. Addition of the glucocorticoid dexamethasone 2.8 ng/h per g BW, to the human GH infusion did not result in estrogen receptor induction. These findings indicate a differential response to human GH administration of Prl receptor and estrogen receptor induction in prepubertal rats. Thus, the so-called ‘ feminizing effect’ of GH (induction of Prl receptors) can be achieved in prepubertal rats whereas a non-sex-differentiated effect of GH (induction of estrogen receptors) could not be evoked in prepubertal rats using the same dose of human GH.