The Neuroendocrine Regulation and Function of Growth Hormone and Prolactin in the Mammalian Fetus*

Abstract

The neural control of fetal pituitary hormone secretion and the conceptualization of the integration of neural, neurotransmitter, neuromodulatory, and humoral signals in the fetus is an emerging field of interest. At an early stage in the construct of the neurosecretory neuron, Berta and Ernst Scharrer (1, 1a) proposed that neurosecretion is a phylogenetically “old and fundamental attribute of neural elements.” Not only is neurosecretion a primitive regulatory system but an increasing body of evidence suggests that neuroendocrine mechanisms differentiate and function from early in fetal life in many mammals, whereas in others with slower neural development this maturation occurs in the perinatal period. Among the earliest studies are those of Jost (2), who observed that decapitation of the male rabbit fetus impaired fetal testicular function. Neurohormones are present in the fetal hypothalamus at the time of its initial differentiation from the primitive forebrain, and it is likely that even before full morphological differentiation of the hypothalamic-pituitary unit, neurosecretions influence fetal anterior pituitary function.