Growth hormone and prolactin in the fetus

Growth hormone is released from pituitary glands maintained in tissue culture as early as 5 weeks after conception. It has been identified in the fetal anterior pituitary gland by immunologic and biologic techniques between 7 and 15 weeks of gestation. Immunoreactive pituitary GH levels increase rapidly between 10 and 14 weeks of gestation to maximal levels at 30-34 weeks. Serum GH levels are detectable by 10-weeks postconception and reach maximal values at 20-24 weeks declining thereafter until term. Pospartum GH concentrations decline over several weeks to lower values, GH levels remaining higher in preterm than in term infants. The biologic role of pituitary GH in the fetus is unknown. Although birth-weights and lengths are reported to be normal in infants with anencephaly, aplasia, or hypoplasia of the pituitary gland and in isolated deficiency of growth hormone, in whom pituitary and serum GH levels are low, careful inspection of large series of such infants reveals that their birthweights may indeed be low and that cell numbers in many organs may be subnormal. In experimental animals prenatal administration of GH increases maternal weight and gestational length. Reported effects on neuronal growth and adult intelligence of animals treated prenatally may reflect these phenomena rather than a direct transplacental effect of GH. Prolactin is also elaborated by the pituitary gland of very young human fetuses. It has been identified immunologically by 10-weeks gestation and biologically at 18 weeks. Pituitary content of immunoreactive prolactin remains low until 16.5-weeks gestation and then increases steadily until term. The plasma concentration of prolactin is low until 30-weeks gestation and increases thereafter until term. In anencephalic fetuses prolactin levels are normal and respond to appropriate stimuli. Very high concentrations of (possibly fetal) prolactin are found in the amniotic fluid. The role of prolactin in the fetus is also unknown. It has been suggested that prolactin may be important for growth of the fetal adrenal cortex and/or for suppression of the immune response during pregnancy. It is apparent that a great deal of additional work is necessary before the importance of either growth hormone of prolactin for normal fetal growth and development will be known.