Somatomedin-C in accelerated growth of children with precocious puberty

To assess the role of somatomedin-C as a possible mediator of the growth spurt in children with central precocious puberty, we compared Sm-C levels in 40 children with central precocious puberty, 87 age-matched normal children, and 110 normal pubertal controls. Somatomedin C levels were significantly elevated for age in the children with precocious puberty (P<0.01), and were similar to the levels observed during normal puberty. The patients with precocious puberty were given the luteinizing hormone releasing hormone analogue d-Trp⁶-Pro⁹-NEt-LHRH (LHRH_a) for 6 months. Treatment caused a significant decrease in secondary sexual characteristics, growth rate, plasma gonadotropins, sex steroids (estradiol in the girls and testosterone in the boys), and Sm-C levels. Growth during LHRH_a treatment returned to the age-appropriate rate, whereas plasma Sm-C levels, although lower than pretreatment levels, remained significantly elevated for age (P<0.002). In addition, growth rates before and during treatment did not correlate with the plasma somatomedin C levels, nor did the decreases in growth rate during LHRH_a therapy correlate with the decreases in somatomedin C levels. Growth rates did correlate significantly, however, with plasma estradiol levels in the girls (P<0.0005) and with plasma testosterone levels in the boys (P<0.025). We conclude that the growth spurt in children with precocious puberty cannot be explained by the plasma level of somatomedin C.