The relationship of plasma gonadotrophins and androgen concentrations to body growth in boys

Abstract

Plasma concentrations of luteinizing hormone (LH), FSH, 17 .alpha.-hydroxyprogesterone (17.alpha.-OPH), androstenedione (.DELTA.4) and testosterone (T) were measured in 543 healthy boys aged 6.0-15.9 yr (with weight and height between the 3rd and 97th percentile for Mexican standards) as a function of chronologic age (CA), weight, height, surface area (SA) and calculated lean body mass (LBM) and total body fat (TBF). The earliest hormonal event was a clear rise in plasma 17.alpha.-OHP, either prior or simultaneous to a steady increase in plasma FSH, far ahead of any sign of puberty. These changes were closely followed by a continuous rise in plasma .DELTA.4. Thereafter, there was a prolonged period of low but progressively increasing plasma FSH levels in the face of constantly low LH levels. A brisk rise in plasma LH and FSH occurred at a mean weight of 35.4 kg, at a height of 144.5 cm and when LBM was 32.0 kg. Simultaneously, plasma 17.alpha.-OHP began to fall, .DELTA.4 reached a plateau and soon after, a marked rise in plasma T was documented. When plasma LH and FSH concentrations were plotted against CA, weight, height, SA and LBM a significant quadratic equation was disclosed in each case. Both gonadotropins did not correlate with TBF. Multiple variance analysis demonstrated that LBM and SA had the most marked effect on LH, while LBM was the most important variable affecting plasma FSH concentrations. The present data suggest the association between a critical level of body composition and the major hormonal events in boys, regardless of a cause-effect relationship. A critical level of LBM (20-23 kg) and not of TBF was attained at time of the initial hormonal changes, and at the time of the major changes in plasma gonadotropins (32-35 kg).