To evaluate the relative changes in serum bioactive (B) and immunoreactive (1) plasma gonadotropin concentrations during pubertal maturation, 28 healthy boys were enrolled at Tanner stage I and followed at 6-month intervals until achievement of Tanner stage V of pubertal maturation. At each visit, a careful interview, complete physical examination, sexual maturation staging, and bone age x-ray study were done, and a blood sample was obtained. Serum concentrations of PRL, dehydroepiandrosterone, and its sulfate, DELTA4-androstenedione, estrone, estradiol, and testosterone (T) were determined by RIA. Samples from 20 boys were assayed for I-LH by RIA and for B-LH by the rat interstitial cell testosterone production assay, using 2 standards [Second International Reference Preparation-Human Menopausal Gonadotropin (2nd IRP-hMG) and LER 960]. Samples from 11 boys (3 from LH group and 8 others) were assayed for I-FSH by RIA and B-FSH by the rat Sertoli cell aromatase induction assay. The results were analyzed by regression analysis for B and I LH and FSH by Tanner stages of puberty, and by correlation of B to I LH and FSH as well as B and I LH and FSH to T. The results from both LH standards correlated well to each other (r = 0.967 and 0.882 for B- and I-LH, respectively), and the data are presented for 2nd IRP-hMG standard. In both groups of boys serum T concentrations increased progressively with pubertal development (P < 0.001). The boys bone age, testicular volume, serum T, dehydroepiandrosterone sulfate, dehydroepiandrosterone, DELTA4-androstenedione, estrone concentrations correlated well with pubertal maturation, similar to previously published data and indicate that this group of boys had progressed through puberty in the expected normal manner. Mean serum I-LH concentrations increased progressively from Tanner stage I to V of puberty (P < 0.001), and serum B-LH exceeded the increase in serum I-LH levels. Mean serum I-LH concentrations were 2.0 +/- 0.1, 2.9 +/- 0.2,4.7 +/- 0.4,6.7 +/- 0.7, and 10.4 +/- 2.0 IU/L 2nd IRP-hMG whereas mean serum B-LH concentrations were 0.8 +/- 0.1, 2.2 +/-0.2,5.9 +/- 0.2,10.3 +/- 1.2, and 22.3 +/- 3.8 IU/L 2nd IRP-hMG for Tanner stages I-V of puberty, respectively. This resulted in a progressive increase of LH B/I ratio with advancing pubertal maturation (P < 0.001). Mean serum I-FSH levels increased progressively between Tanner stages I-III of puberty (1.2 +/- 0.1, 1.5 +/- 0.1, and 2.0 +/- 02 ng/mL hFSH-3 respectively, P < 0.05), remained similarly high at Tanner stage IV (2.1 +/- 0.2 ng/ml) and declined by Tanner stage V (1.6 +/- 0.1 ng/mL, P < 0.05 as compared to Tanner IV). In contrast, serum B-FSH concentrations did not change between pubertal stages (2.8 +/- 0.4, 2.4 +/- 0.3, 3.0 +/- 0.4, 3.0 +/- 0.4, and 3.5 +/- 0.7 I-V, respectively). These relatively constant B-FSH concentrations caused the FSH B/I ratio to reciprocally reflect changes in I-FSH Serum B and I-LH correlated well with changes of serum T concentrations for all stages of pubertal development (r = 0.836 and r = 0.674 for B and I-LH, respectively, P < 0.001). Serum B-LH and I-LH also correlated well (r = 0.70, P < 0.001). Serum I-FSH also correlated well with serum T concentrations (r = 0.432, P < 0.01) whereas serum B-FSH concentrations did not correlate with serum T concentrations. We, therefore conclude that unlike serum B and I-LH and serum I-FSH concentrations serum B-FSH concentrations do not demonstrate significant changes with progression of pubertal maturation in boys. Thus, we propose that these differences in the changes of B-LH and B-FSH concentrations during pubertal maturation provide an indirect evidence for a differential regulation of their secretion during sexual maturation in boys.
