Sexual dimorphism in circulating monomeric and dimeric inhibins in normal boys and girls from birth to puberty.
OBJECTIVE
Inhibins are peptides, mainly of gonadal origin, that suppress FSH production. Dimeric forms of inhibin (A and B) have been proposed as peripheral markers of Sertoli and granulosa cell function. The aim of this study was to establish the relationship between circulating dimeric and monomeric inhibins, and gonadotrophins and sex steroids, in normal boys and girls from birth to puberty.


METHODS
One hundred and forty-six normal children (females: 57; males: 89) were studied.


METHODS
Serum LH and FSH were measured by an immunofluorometric assay. Serum oestradiol and testosterone were measured by radioimmunoassay. Serum inhibin A and B, and Pro-alphaC, were measured by specific two-site enzyme-linked immunosorbent assays.


RESULTS
In boys from birth to 6 months of age, the mean serum inhibin B concentration was as high (477 +/- 53.7 ng/l) as that found at puberty (400 +/- 70.2 ng/l). After the first year, inhibin B gradually decreased to reach its lowest concentration (153 +/- 23.6 ng/l) at age 4-6 years. At approximately age 10, it rose progressively to reach pubertal concentrations. Pro-alphaC showed a similar pattern but at lower concentrations. Inhibin A was not detected at any age. In girls from birth to 6 months, inhibin B levels (83.0 +/- 18.3 ng/l) were approximately 50% lower than those found at puberty (181 +/- 25.7 ng/l). After 6 months of age, these levels dropped (17.5 +/- 1.6 ng/l) and remained low until the prepubertal years. Thereafter, they increased to pubertal concentrations. The serum inhibin A concentration after birth (29.9 +/- 8.7 ng/l) was similar to that found at puberty (18.3 +/- 5.7 ng/l); after 6 months, it fell to undetectable levels until the prepubertal years.


CONCLUSIONS
The sex difference in serum levels of gonadotrophins is associated with sex differences in the levels and proportions of circulating dimeric and monomeric inhibins.
Bergadá
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I
Centro de Investigaciones Endocrinológicas, Hospital de Niños 'Ricardo Gutierrez', Buenos Aires, Argentina.
Rojas
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G
Ropelato
G
G
Ayuso
S
S
Bergadá
C
C
Campo
S
S
D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D015415:Biomarkers / Q000097:blood; D002648:Child; D002675:Child, Preschool; D004797:Enzyme-Linked Immunosorbent Assay; D004958:Estradiol / Q000097:blood; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007265:Inhibins / Q000097:blood*; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D010455:Peptides / Q000097:blood; D029584:Prostatic Secretory Proteins; D020033:Protein Isoforms / Q000097:blood; D011498:Protein Precursors / Q000097:blood; D012727:Sex Characteristics; D013739:Testosterone / Q000097:blood
D015415:Biomarkers; D010455:Peptides; D029584:Prostatic Secretory Proteins; D020033:Protein Isoforms; D011498:Protein Precursors; C043076:beta-microseminoprotein; C095971:inhibin-alpha subunit precursor; D013739:Testosterone; D004958:Estradiol; D007265:Inhibins; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone