Characterization of serum SHBG isoforms in prepubertal and pubertal girls.
OBJECTIVE
SHBG is a circulating glycoprotein that binds dihydrotestosterone, testosterone and oestradiol with high affinity and low capacity. In girls, serum concentrations of SHBG gradually decrease with age due to a true fall in concentration and not to a change in the binding characteristics. The aim of our study was to determine the pattern of serum SHBG isoforms in normal girls in early childhood (ECh), late childhood (LCh) and puberty (P).


METHODS
Fifteen normal girls were studied. They were divided into three groups according to their age: ECh: 3.7 +/- 0.9 years (mean +/- SD, n = 5); LCh: 6.4 +/- 0.5 years (n = 5); and P: 13.4 +/- 1.5 years (n = 5).


METHODS
Preparative isoelectric focusing was used to isolate SHBG isoforms according to their isoelectric point (pI). Three groups of isoforms were isolated: SI: pI 5.2-5.4; SII: pI 5.4-5.6 and SIII: pI 5.6-5.8. Steroid levels in serum were determined by RIA.


RESULTS
The relative distribution of SHBG isoforms (% of the total SHBG recovered, mean +/- SD) in the three groups of girls studied was: ECh: SI: 25.8 +/- 9.9, SII: 53 +/- 10.5 and SIII: 21.2 +/- 1.6; LCh: SI: 8.8 +/- 3.1, SII: 58.8 +/- 12.2 and SIII: 31.8 +/- 8.6; P: SI: non-detectable; SII: 51.6 +/- 12.6 and SIII: 48.4 +/- 12.6.


CONCLUSIONS
These results indicate that serum SHBG is more heterogeneous before puberty. A considerable proportion of acidic isoforms are present early in life; they decrease during the prepubertal period and disappear when sexual development is completed. After puberty the glycoprotein is more homogeneous and an important proportion of more basic isoforms is present. At puberty serum SHBG not only falls in concentration but also has an altered sialic acid content which modulates its circulating half-life.
Bedecarrás
P
P
Centro de Investigaciones Endocrinológicas (CEDIE), Hospital de Niños Ricardo Gutierrez, Buenos Aires, Argentina.
Gryngarten
M
M
Ayuso
S
S
Escobar
M E
ME
Bergadá
C
C
Campo
S
S
D000293:Adolescent; D000704:Analysis of Variance; D002648:Child; D002675:Child, Preschool; D019314:Dehydroepiandrosterone Sulfate / Q000097:blood; D004958:Estradiol / Q000097:blood; D005260:Female; D005498:Follicular Phase / Q000097:blood; D006207:Half-Life; D006801:Humans; D007525:Isoelectric Focusing; D019158:N-Acetylneuraminic Acid / Q000032:analysis; D020033:Protein Isoforms / Q000032:analysis; D011627:Puberty / Q000097:blood*; D012738:Sex Hormone-Binding Globulin / Q000032:analysis* / Q000737:chemistry; D013739:Testosterone / Q000097:blood
D020033:Protein Isoforms; D012738:Sex Hormone-Binding Globulin; D013739:Testosterone; D004958:Estradiol; D019314:Dehydroepiandrosterone Sulfate; D019158:N-Acetylneuraminic Acid