ONTOGENY OF GONADOTROPIN, TESTOSTERONE, AND INHIBIN SECRETION IN NORMAL BOYS THROUGH PUBERTY BASED ON OVERNIGHT SERIAL SAMPLING

To investigate hormonal changes occurring in male puberty, we measured LH, FSH, testosterone, and a-inhibin immunoactivity in serum samples drawn every 10 min For 8 h (2100-0500 h) From each of 50 normal prepub ertal and pubertal boys, aged 8.4-18.8 yr. We measured gonadotropins w ith ultrasensitive immunofluorometric assays, and testosterone and a-i nhibin with RIAs. Unlike previous studies, which indexed pubertal deve lopment with Tanner stages, we used testicular volume, a more finely g raduated indicator of development, to reveal patterns that were obscur ed when subjects were grouped by Tanner stage. The overnight mean conc entration of each hormone increased with testis volume, but the rate o f increase on a logarithmic scale slowed as testes grew. Log LH rose p recipitously in the late prepubertal and early pubertal periods and pl ateaued during mid and late puberty. Based on fitted regression curves , LH increased about 20-fold (from 0.11 IU/L) between testis volumes o f 1 and 10 mt, but only an additional 1.5-fold by 30 mt. The developme ntal trajectory of log testosterone was like that of log LH, but rose less steeply early in puberty. From 0.14 mu g/L at a testis volume of 1 mt, testesterone increased about 8.5-fold by 10 mL and an additional 9-fold by 30 mt. In contrast, logarithms of overnight mean FSH and al pha-inhibin concentrations rose at a more nearly constant rate through out puberty. From 0.62 IU/L at a testis volume ol mt, the FSH concentr ation doubled by 10 mL and increased an additional 1.7-fold by 30 mt. From 270 ng/L at a testis volume of 1 mt, inhibin increased 1.5-fold b y 10 mt and an additional 1.3-fold by 30 mt. Overnight pulse amplitude s exhibited developmental trajectories similar to those of the corresp onding overnight mean concentrations. The number of LH and testosteron e pulses during the sampling period averaged 2.2 and 2.1, respectively , at Tanner stage 1 and increased to 4.5 and 3.2, respectively, at Tan ner stage 5. The number of FSH and inhibin pulses remained constant th roughout puberty, averaging 3.3 and 3.5, respectively. Pairwise correl ations among hormone concentrations were strong. reflecting common inc reasing trends through puberty; however. after accounting for developm ental trends, FSH, LH, and testosterone concentrations remained correl ated, whereas inhibin was uncorrelated with each of the other three ho rmones. Measuring gonadotropins with ultrasensitive assays and analyzi ng the results on a logarithmic scale as a function of testis volume m ade clear the dramatic hormonal changes that begin before the clinical changes of puberty.