Somatomedin activity in cystic fibrosis and reserpinized rats: possible explanation for growth retardation

Somatomedin activity in children who have cystic fibrosis is reduced to approximately 50 percent of the levels found in normal children. In contrast, the growth hormone concentration in these patients, both the resting and the stimulated levels, was found to be no different from normal children (17.2 and 18.4 ng per ml, respectively). Reserpinized rats have been proposed as a model for cystic fibrosis. Serum somatomedin activity in rats treated with reserpine (0.50 mg per kg per d x 7 days) was reduced to 30 percent of the levels measured in control rats. Reserpine also decreased radiosulfate incorporation into cartilage glycosaminoglycan (GAGS) in vivo and in vitro. Fasting decreased serum somatomedin activity as well as the concentration of GAGS in rat cartilage. Refeeding for 24 hours restored these parameters to normal. These data suggest that one mechanism for the growth retardation occurring in patients who have cystic fibrosis may be explained by decreased serum somatomedin activity.