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      Activation of the Hypothalamic-Pituitary-Gonadal Axis in Infancy: Minipuberty

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          The hypothalamic-pituitary-gonadal (HPG) axis is active in the midgestational foetus but silenced towards term because of the negative feedback effects mediated by the placental hormones. This restraint is removed at birth, leading to reactivation of the axis and an increase in gonadotrophin levels. Gonadotrophin levels are high during the first 3 months of life but decrease towards the age of 6 months except for FSH levels in girls that remain elevated until 3-4 years of age. After this, the HPG axis remains quiescent until puberty. The postnatal gonadotrophin surge results in gonadal activation in both sexes. In boys, testosterone levels rise to a peak at 1-3 months of age and then decline following LH levels. Postnatal HPG axis activation is associated with penile and testicular growth and therefore considered important for the development of male genitalia. In girls, elevated gonadotrophin levels result in the maturation of ovarian follicles and in an increase in oestradiol levels. Biological significance and possible long-term consequences of this minipuberty remain elusive, as do the mechanisms that silence the HPG axis until puberty. However, the first months of life provide a ‘window of opportunity' for functional studies of the HPG axis prior to pubertal development.

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          Most cited references 58

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          Changes in anti-Müllerian hormone (AMH) throughout the life span: a population-based study of 1027 healthy males from birth (cord blood) to the age of 69 years.

          Anti-Müllerian hormone (AMH), which is secreted by immature Sertoli cells, triggers the involution of the fetal Müllerian ducts. AMH is a testis-specific marker used for diagnosis in infants with ambiguous genitalia or bilateral cryptorchidism. The aim of the study was to describe the ontogeny of AMH secretion through life in healthy males. This was a population-based study of healthy volunteers. PARTICIPANTS included 1027 healthy males from birth (cord blood) to 69 yr. A subgroup was followed up longitudinally through the infantile minipuberty [(in cord blood, and at 3 and 12 months), n=55] and another group through puberty [(biannual measurements), n=83]. Serum AMH was determined by a sensitive immunoassay. Serum testosterone, LH, and FSH were measured, and pubertal staging was performed in boys aged 6 to 20 yr (n=616). Serum AMH was above the detection limit in all samples with a marked variation according to age and pubertal status. The median AMH level in cord blood was 148 pmol/liter and increased significantly to the highest observed levels at 3 months (P<0.0001). AMH declined at 12 months (P<0.0001) and remained at a relatively stable level throughout childhood until puberty, when AMH declined progressively with adults exhibiting 3-4% of infant levels. Based on this extensive data set, we found detectable AMH serum levels at all ages, with the highest measured levels during infancy. At the time of puberty, AMH concentrations declined and remained relatively stable throughout adulthood. The potential physiological role of AMH and clinical applicability of AMH measurements remain to be determined.
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            Time course of the serum gonadotropin surge, inhibins, and anti-Müllerian hormone in normal newborn males during the first month of life.

            Newborns with ambiguous genitalia or males with nonpalpable gonads usually require an early assessment of the presence and functional state of testicular tissue. Our objective was to characterize the precise ontogeny of the serum patterns of gonadotropins, testosterone, anti-Müllerian hormone (AMH), and inhibins in normal newborn boys. We conducted a cross-sectional and longitudinal study. Serum samples were obtained in 57 boys and 13 girls on d 2 of life. A second sample was obtained on d 7, 10, 15, 20, and 30 (boys) and on d 30 (girls). Serum levels of gonadotropins, testosterone, AMH, and inhibins were measured. In males, LH and FSH were undetectable or very low on d 2. By d 7, LH increased to 3.94 +/- 3.19 IU/liter (mean +/- sd) and FSH to 2.04 +/- 1.67 IU/liter. LH/FSH ratios were 0.40 +/- 0.11 (d 2) and 2.02 +/- 0.20 (d 30). AMH rose from 371 +/- 168 pmol/liter (d 2) to 699 +/- 245 pmol/liter (d 30), and inhibin B rose from 214 +/- 86 ng/liter (d 2) to 361 +/- 93 ng/liter (d 30). The inhibin alpha-subunit precursor (pro-alphaC) remained stable during the first month of life. Testosterone levels were 66 +/- 42 ng/dl (d 2), 82 +/- 24 ng/dl (d 20), and 210 +/- 130 ng/dl (d 30). A sexual dimorphism was observed in AMH and inhibin B (lower in girls on d 2 and 30), in LH/FSH ratio (lower in girls on d 30) and in testosterone (lower in girls on d 30). Sertoli cell markers AMH and inhibin B are the earliest useful markers indicating the existence of normal testicular tissue.
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              Pituitary-gonadal relations in infancy: 2. Patterns of serum gonadal steroid concentrations in man from birth to two years of age.

              Testosterone, estradiol, 170H-progesterone, and androstenedione (except in cord samples) concentrations were determined in cord sera (30 male and 14 female) and in peripheral sera from infants (121 male and 110 female), age 1 day to 2 years. Male and female cord serum levels of these steroids were not significantly different. In both sexes levels during the first week were lower than those in cord sera. In male infants serum testosterone and 170H-progesterone levels rose sharply in the second week of life, reached a peak at 1-2 months, and then declined to the range seen in later childhood by 6 months of age; male serum androstenedione and estradiol concentrations were higher during the first 2 months of life, but no distinct pattern of rise and fall was seen. In girls serum testosterone levels fell in the first week to the range seen throughout childhood; serum concentration of estradiol, androstenedione, and 17OH-progesterone in girls were markedly variable, with many values above the childhood range being seen, particularly in the first 6 months. These data provide further evidence of active Leydig cell function in male infants. They suggest that there is also ovarian secretion of sex steroids in some female infants in response to the elevated FSH and LH levels which are seen at this time.

                Author and article information

                Horm Res Paediatr
                Hormone Research in Paediatrics
                S. Karger AG
                August 2014
                05 July 2014
                : 82
                : 2
                : 73-80
                aDepartment of Pediatrics, Kuopio University Hospital, University of Eastern Finland, Kuopio, Finland; bWilliam Harvey Research Institute, Barts and the London Queen Mary University of London, London, UK
                Author notes
                *Prof. Leo Dunkel, William Harvey Research Institute Barts and the London Queen Mary University of London, London EC1M 6BQ (UK), E-Mail l.dunkel@qmul.ac.uk
                362414 Horm Res Paediatr 2014;82:73-80
                © 2014 S. Karger AG, Basel

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