Effect of bromocriptine treatment on circulating somatomedins in tall adolescents.

Somatomedin and bromocriptine levels were measured before and after 3 months of bromocriptine treatment (5 mg/day) in the sera of 16 tall adolescents with excessive adult height prediction. Somatomedins were measured by RIA for somatomedin C and IgFII and by measuring thymidine incorporation into human lectin-activated lymphocytes. Mean +/- SEM levels of bromocriptine after three months of treatment were 0.61 +/- 0.08 ng/ml. No changes in radioimmunoassayable somatomedin C were observed after bromocriptine intake respectively 1.34 +/- 0.17 U/ml before and 1.4 +/- 0.01 U/ml during treatment. On the opposite a significant decrease of thymidine activity (p less than 0.002) from 1.45 +/- 0.17 U/ml to 1.12 +/- 0.19 U/ml was observed. No changes of IgFII levels were observed in the sera of the 8 patients where they were measured. In order to test a possible direct effect of bromocriptine on peripheral tissues bromocriptine mesylate was added in somatomedin bioassays. Inhibitory effect of bromocriptine in vitro is seen at higher levels (1 microM) compared to the circulating one (1 nM). This study demonstrates that the major effect of bromocriptine which is the acceleration of bone maturation is not related to changes in somatomedin C.