Plasma Glycoprotein Hormone α-Subunit in the Neonate and in Prepubertal and Pubertal Children: Effects of Luteinizing Hormone-Releasing Hormone*

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Abstract
We studied the changes with maturation in the concentration of plasma glycoprotein hormone a-subunit in the basal state and after the administration of LRF. In samples of cord blood from 27 fullterm newborns, a-subunit exceeded 10 ng/ml. Plasma samples from 65 infants over 1 day of age showed a rapid decline in a-subunit to less than 1 ng/ml in most cases; a longitudinal study of a-subunit in 4 neonates confirmed the decrease. Twelve adult males had basal a-subunit concentrations and peak concentrations after LRF of 1.0 ± 0.1 and 3.7 ± 0.1 ng/ ml (mean ± SEM), respectively; pubertal females had concentrations of 0.8 ± 0.3 and 3.7 ± 0.8; and pubertal males had concentrations of 0.7 ± 0.1 and 2.7 ± 0.4; prepubertal females had concentrations of 0.3 ±0.1 and 1.1 ± 0.2; and prepubertal males had concentrations of 0.4 ±0.1 and 1.0 ± 0.1. In 5 girls with true precocious puberty, the basal plasma a-subunit concentration was 0.5 ± 0.3 ng/ml and peak a-subunit concentration was 2.7 ± 1.0. Statistical analysis showed that mean peak a-subunit concentrations in prepubertal males and females were significantly different than those in the pubertal, precocious pubertal, and adult groups. There was no sex difference in a-subunit concentrations. Analysis of the integrated area under the response curve for a-subunit after LRF showed the same statistical results. Plasma /SLH concentrations were below 0.5 ng/ml in all samples. Analysis of plasma human LH and human FSH after LRF was in agreement with normal values in relation to stages of secondary sexual development; the peak of human LH was higher in pubertal, precocious pubertal, and adult subjects than in prepubertal children, with no sex difference, while there was no significant change in human FSH with maturation, although females had higher concentrations than males. In summary, we found that 1) in the neonate, plasma α-subunit concentrations parallel changes in hCG, while in postnatal subjects, the asubunit concentrations parallel changes in the secretion of pituitary LH; 2) the pituitary secretion of α-subunit appears to be under hypothalamic control similar to that of the secretion of human LH; and 3) the production of β-glycoprotein hormone subunit is a rate-limiting step in the synthesis of hCG and human LH.