Bioassayable Luteinizing Hormone during Childhood and Adolescence and in Patients with Delayed Pubertal Development*

Abstract

It has recently been reported that measurements of bioassayable (B-)serum LH may be superior to those of immunoassayable (I-) LH in the detection of normal and precocious puberty. To examine the discriminating value of these two parameters, serum B- and I-LH were measured in 126 normal subjects (Tanner stages I-V), 8 infants, and 21 patients with delayed adolescence. B-LH was detectable i only 16% of prepubertal children, while I-LH was measurable in all such subjects Between puberty and adulthood, there was a 12- to 14- fold rise in B-LH, in contrast to only a 4-fold increment in I-LH. The resulting B to I ratio of LH also rose significantly in both sexes between prepubertal years and later stages of puberty. In the 21 patients with delayed adolescence, the B-LH was below the mean ± 2 SEM in all subjects, whereas the I-LH was outside these limits in 16 cases. In 1 patient with delayed adolescence, the B-LH and I-LH were comparabl during a 24- sampling period, except for the nocturnal peak during which the level of serum B-LH exceeded that of the LH. To resolve the differences between the finding of undetectable B-LH in prepubertal samples and previously reported data, we performed several modifications of the in vitro rat interstitial cell testosterone production assay. 1) When bovine serum albumin was substituted for estrogen-suppressed serum to equalize the protein content within the samples and the standard curve, the final B-LH values were significantly higher (P<0.001). 2)The sensitivity of the assay was increased 3-fold by the method of Solano et al. (11,12). 3) Pure L standard [1 mg is equivalent to 9375 IU Second International Reference Preparation of human menopausal gonadotropin (IRP-2-hMG)] was substitute for the IRP-2-hM standard. In spite of the latter two modifications, the number ofsamples from prepubertal children with undetectable serum B-LH remained the same.The B to I ratio of serum LH using the purer LH was 0.82± 0.11, significantly lower (P < 0.001) than that achieved using the IRP-2-hMG (2.2 ±0.27). During pubertal development, a rise in the B to I ratio of serum LH was nonetheless noted. In conclusion: 1) B-LH concentrations were measurable only in16% of prepubertal children; 2) I-LH concentrations were detectable in all prepubertal children; 3) B-LH concentrations rose more dramatically with successivestages of pubertal development than did I-LH concentrations; 4) the B to I ratio of LH rose during puberty; and 5) measurements of B-LH did not provide a better discriminator of delayed puberty than measurements of I-LH.