Hypothalamic-pituitary-gonadal relationships in man from birth to puberty.

Abstract

It is believed that the study of gonadal function of the child should be regarded as a whole, beginning with the fetus and ending with the adolescent. Gonadal function depends upon 3 levels of activities: 1) central level (extra-hypothalamic, hypothalamic, and anterior pituitary); 2) an intermediate level (gonadal and plasma), and 3) a peripheral level consisting of the target organs to which the hormonal message is directed. These activities determine both the expression of gonadal function (physical, physiological, or psychological) and the feedback regulation of gonadotropin secretion. There are 4 main phases of development of gonadal function: fetal, perinatal, prepubertal, and pubertal. The fetal phase begins with testosterone secretion around the 8th week in utero under the control of the chorionic gonadotropin. Gonadotropin secretion by the pituitary becomes established during the 12th week. During the 2nd half of fetal life, negative feedback becomes gradually established, appearing more rapidly in boys than in girls. In the perinatal phase, the hypothalamic-pituitary activity accounts for the testicular and probably ovarian secretion which has been demonstrated to occur during the 1st 6 months of life. Threshold sensitivity of the gonadostat to steroid inhibition appears high during the 1st 3 months of life, progressively declining to the very low level characteristic of childhood. The gonadostat is least active during the prepubertal phase, subsequently being more active under the influence of adrenocortical steroids. This hypothalamic activity accounts for the gradual increase of the pituitary and gonadal sensitivity to their respective stimuli. In the pubertal phase, the gonadostat threshold rapidly increases and secondary sexual characteristics and reproductive capacity start developing. 2 specific phenomena occur, large nocturnal discharges of luteinizing hormone and testosterone, and the establishment of positive feedback control by estrogens which permits ovulation.