The roles of placental growth hormone and placental lactogen in the regulation of human fetal growth and development

The human growth hormone (hGH)/human placental lactogen (hPL) gene family, which consists of two GH and three PL genes, is important in the regulation of maternal and fetal metabolism and the growth and development of the fet us. During pregnancy, pituitary GH (hGH-N) expression in the mother is supp ressed; and hGH-V, a GH variant expressed by the placenta, becomes the pred ominant GH in the mother. hPL, which is the product of the hPL-A and hPL-B genes, is secreted into both the maternal and fetal circulations after the sixth week of pregnancy. hGH-V and hPL act in concert in the mother to stim ulate insulin-like growth factor (IGF) production and modulate intermediary metabolism, resulting in an increase in the availability of glucose and am ino acids to the fetus. In the fetus, hPL acts via lactogenic receptors and possibly a unique PL receptor to modulate embryonic development, regulate intermediary metabolism and stimulate the production of IGFs, insulin, adre nocortical hormones and pulmonary surfactant. hGH-N, which is expressed by the fetal pituitary, has little or no physiological actions in the fetus un til late in pregnancy due to the lack of functional GH receptors on fetal t issues. hGH-V, which is also a potent somatogenic hormone, is not released into the fetus. Taken together, studies of the hGH/hPL gene family during p regnancy reveal a complex interaction of the hormones with one another and with other growth factors. Additional investigations are necessary to clari fy the relative roles of the family members in the regulation of fetal grow th and development and the factors that modulate the expression of the gene s.