Bioactivity of luteinizing hormone during normal puberty in girls and boys

In order to evaluate the in vitro bioactivity of LH during normal puberty c ompared to LH immunoactivity measured in a highly sensitive immunoassay, bl ood plasma samples from healthy children were analyzed in a mouse Leydig ce ll assay (MLCA). Blood samples were obtained Rom 60 healthy girls and boys during normal pubertal development. Samples were taken on two occasions wit h a 1-year interval. Three daytime samples and three nighttime samples were analyzed. The correlation of the LH immunoradiometric assay (IRMA) activit y with the LH activity in the MLCA varied from 0.60 to 0.96 in the differen t pubertal stages, During pubertal development, a gradually increase in the activity of LH in both the IRMA and MLCA was found. The ratio of the in vi tro bioactivity compared to the immunoreactivity (B/I ratio) did not change significantly during puberty: it was 0.84 (SD 0.58) and 0.66 (SD 0.40) dur ing the first and second sampling period in girls and 0.88 (SD 0.38) and 0. 91 (SD 0.46, NS) in the boys. The B/I ratio of LH does nor change during pu berty. With a high sensitivity and specificity, measurement of LH by IRMA g ives representative measurements of the LH in vitro bioactivity in children during pubertal development. Copyright (C) 1999 S. Karger AG, Basel.