Effect of Gonadotropin-Releasing Hormone on Pituitary-Gonadal Function of Male Infants during the First Year of Life*

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Abstract
To investigate the regulatory mechanism resulting in the postnatal elevation of male serum testosterone (T), we performed GnRH stimulation tests on 14 3- to 390-day-old male infants with unilaterally or bilaterally undescended testes. The subjects were arranged according to postnatal age in the following groups: 3–6, 23–37, 58–105, and 280–390 days. The subjects investigated had normal basal T, LH, and FSH levels. The basal levels of LH were highest in the age groups of 3–6 and 23–37 days (means, 8.4–8.6 IU LH/liter); the basal FSH level was highest at 23–37 days (mean, 3.6 ± 0.7 IU FSH/liter), and the 210- to 390-day-old group had 50–70% lower gonadotropin levels. Basal T increased 3-fold (P < 0.001) between 3–6 and 23– 37 days (from 0.65 ± 0.12 to 1.86 ± 0.25 μg/liter), decreasing thereafter to very low levels by 210–390 days (below 0.1 /μg/liter). A single iv injection of 50 /μg/m2 GnRH was given, and plasma LH, FSH, and T were measured at -30, 0, 30, 60, and 120 min in relation to the injection. GnRH-Stimulated LH and FSH levels increased 3-fold from the age group of 3–6 days to that of 23–37 days (P < 0.05), and the stimulability of pituitary gonadotropin secretion decreased gradually thereafter. Despite a clear elevation of stimulated LH, serum T was not significantly increased in any of the age groups during the 2-h observation period. It is concluded that during the postnatal period: 1) The pituitary LH and FSH response to GnRH stimulation increases after birth, reaching a maximum between 1–3 months of postnatal age, but then declining clearly between 3–12 months of age; 2) The postnatal T peak is associated with maximal response of gonadotropins to GnRH stimulation; 3) In all age groups, even the youngest, a clear, rapid response of serum T to gonadotropin stimulation was lacking; and 4) The decline of serum T towards 1 yr of age is associated with decreased basal and GnRH-stimulable gonadotropin levels.(J Clin Endocrinol Metab55: 689, 1982)