Serum bioactive (B) LH concentrations increase with each pubertal stage and exceed immunoreactive (I) measurements in boys and girls throughout puberty. These results have been attributed to increased GnRH secretion and/or sex steroid modulation. FSH secretion is likewise affected by these factors. We, therefore, tested the hypothesis that serum B-FSH concentrations would increase with each stage of puberty in boys and girls. In this study we compared the serum concentrations of B-FSH, I-FSH, and sex steroids and stages of puberty (determined according to Tanner) in 111 sera obtained from boys and girls from 6-18 yr of age with the results obtained from 6 young men under the age of 35 yr and 13 cycling women (studied during the follicular, periovulatory, and luteal phases of their menstrual cycles). The serum I-FSH, testosterone (T), and estradiol (E2) concentrations were determined by RIAs, and B-FSH was determined by the rat Sertoli cell aromatase induction assay. The results were analyzed by one-way analysis of variance followed by Scheffe’s test for each gender and two-way analysis of variance followed by Student-Newman-Keuls test for comparison of the results between sexes. In boys the mean serum T concentrations increased progressively with each stage of pubertal development up to Tanner stage 4 (P < 0.01). The mean serum I-FSH concentration at Tanner stage 1 was 0.7 ± 0.1 ng/mL (hFSH-3) and did not change significantly until Tanner stage 4, when it was increased to 3.7 ± 1.0 ng/mL (P < 0.05). The mean serum I-FSH concentrations for Tanner stage 5 and adult men were not statistically different, but were lower than in Tanner stage 4. Mean serum B-FSH concentrations measured with the same standard were 1.9 ± 0.4, 3.1 ± 0.4, 2.7 ± 0.4, 4.2 ± 1.4, and 3.6 ± 0.3 ng/mL in Tanner stages 1-5, respectively. These were not significantly different. In girls the mean serum E2 concentrations increased progressively between the Tanner stages (P < 0.00005, by twoway analysis of variance). Mean serum I-FSH levels did not change significantly with the achievement of different pubertal stages. The mean B-FSH concentrations were 2.7 ± 0.4, 2.8 ± 0.5, 3.8 ± 0.8, 2.8 ± 0.7, and 3.9 ± 0.6 ng/mL at Tanner stages 1-5, respectively, and were, likewise, not statistically significantly different. In adult women the mean serum B-FSH concentrations during the follicular phase of the menstrual cycle were not significantly different from pubertal values. On the other hand, as previously reported and confirmed here, in the presence of elevated serum E2 levels during the periovulatory phase of the menstrual cycles, serum B-FSH concentrations significantly exceeded all other values during puberty and the IFSH levels, resulting in a significantly higher B/I ratio of FSH. Mean serum B-FSH concentrations during the luteal phase of the cycle were significantly lower than those during puberty or the other menstrual cycle phases. Comparisons of serum B-FSH concentrations between boys and girls revealed no significant differences between the sexes at any stage of puberty. The mean I-FSH concentrations were higher in girls than boys at Tanner stages 1, 2, 3, and 5. The resulting FSH B/I ratios were significantly higher in boys than in girls (P < 0.00005) at each Tanner stage of puberty (P = 0.002, by two-way analysis of variance). © 1990 by The Endocrine Society.
