Changes in growth and serum growth hormone and plasma somatomedin-C levels during suppression of gonadal sex steroid secretion in girls with central precocious puberty.

Suppression of gonadal sex steroid secretion in children with central precocious puberty (CPP) by LHRH analogs affords an opportunity to study sex steroid modulation of GH and somatomedin-C (Sm-C) secretion and to examine the role of GH and Sm-C in pubertal and prepubertal statural growth. Nocturnal serum GH and plasma Sm-C levels were measured in 10 preadrenarchal girls [mean age, 3.0 +/- 0.6] ( +/- SEM) yr with CPP before and during 2 yr of LHRH analog-induced gonadal suppression. Their mean height velocity, initially 4.6 +/- 0.6 ( +/- SEM) SD above the mean for chronological age, decreased to -0.1 +/- 0.4 SD during 12-24 months of ovarian suppression (P less than 0.00005). The mean peak nocturnal plasma GH level was 22.5 +/- 5.4 ( +/- SEM) micrograms/L during puberty, and it decreased to 10.2 +/- 2.1 micrograms/L after 3 months of suppression of gonadarche. This decrease persisted throughout the 2 yr of gonadal suppression (P less than 0.05). The reduction in GH secretion was accompanied by a decrease in mean plasma Sm-C levels from 3.5 +/- 0.7 to 1.5 +/- 0.2 U/mL after 3 months of suppression of gonadal sex steroids, which persisted during 2 yr of gonadal suppression (P less than 0.01). Suppression of ovarian function in girls with CPP results in decreased height velocity. This slowing of growth occurs in association with decreased nocturnal serum GH and plasma Sm-C levels, suggesting that acceleration of growth during puberty is partially mediated by sex steroid-induced augmentation of GH secretion.