No abstract

Plasma concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), 17 alphahydroxyprogesterone (17\g=a\-OPH),androstenedione (\ g=D\ 4) and testosterone (T) were measured in 543 healthy boys aged 6.0 to 15.9 years (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\g=a\-OHP, either prior or simultaneously to at steady increase in plasma FSH, far ahead of any sign of puberty. These changes were closely followed by a continuous rise in plasma \ g=D\ 4. Thereafter, there was a prolonged period of low but progressively increasing plasma FSH levels in the face of constantly low LH levels. However, 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\g=a\-OHP began to fall, \ g=D\ 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 gonadotrophins 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 causeeffect relationship. A critical level of LBM (20\p=n-\23 kg) and not of TBF was attained at time of the initial hormonal changes, as well as at the time of the major changes in plasma gonadotrophins (32\p=n-\35 kg).

Plasma concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), 17 alpha-hydroxyprogesterone (17\g=a\-OHP),17\g=b\-oestradiol (Oe2) and progesterone (P) were measured in 352 healthy girls aged 6.0 to 15.9 years, as a function of age (CA), weight, height and calculated lean body mass (LBM) and total body fat (TBF). The earliest hormonal changes were a fall in mean plasma FSH concentrations together with a small but significant rise in plasma Oe2 well in advance of any sign of pubertal development. The next changes were a progressive rise in plasma FSH and 17\g=a\-OHPconcentrations without further increments in plasma Oe2 ; these changes corresponded to a mean body weight of 29.8 kg, a mean height of 132.0 cm (initiation of the adolescent growth spurt), a mean LBM of 24.7 kg and a mean TBF of 5.1 kg. The last events were a progressive rise in plasma LH and Oe2 and less marked in P, which occurred in association with a mean body weight of 40.0 kg, a mean height of 142.0 cm (time of peak velocity of weight and height gain), a mean LBM of 31.8 kg and a mean TBF of 9.1 kg. Significant quadratic equations were disclosed between plasma FSH and LH versus CA, weight, height and LBM, and a significant linear correlation was observed between each gonadotrophin and TBF. These results show an association, not necessarily causal, between a 'critical level' of body composition and hormonal changes at the start of the adolescent growth spurt, as well as with late hormonal events at the time of peak velocity in weight and height gain. On the other hand, LBM rather than TBF seems more closely associated with the initiation and progression of puberty.

Levels of haemoglobin (Hb), haematocrit (Ht) and mean corpuscular haemoglobin concentration (MCHC) were determined in 523 boys and 350 girls, clinically healthy, ages 6-0 to 13-5 years, middle socio-economic class living in Mexico City. In girls no significant differences according to age were observed in Hb or MCHC; however, Ht was significantly greater at 10-5 than at 10-0 years, without subsequent modifications. In boys, Hb and Ht had a first increase between 10-5 and 11-0 years and a second rise from 12-5 years on: MCHC remained unchanged. Boys were six to twelve months behind girls in regard to Ht increase; however, Ht increased when boys and girls reached similar mean weights (34 kg), heights (138 cm) and surface areas (1-15 m2); concomitantly, they had progressed to stage 2 of sexual development. Clear sex differences began to appear at age 11-5 when boys had higher Hb and Ht values than girls. These data suggest that Hb and Ht changes in these children are not related to chronological age but can be better interpreted if compared to weight, height, surface area or stage of sexual development.