Insulin-Like Growth Factors (IGFs) in Pygmies and Subjects with the Pygmy Trait: Characterization of the Metabolic Actions of IGF I and IGF II in Man*

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Abstract
Twenty-two pygmy subjects in addition to 11 previously studied pygmies were shown to have low serum concentrations of insulin-like growth factor I (IGF I) and normal serum concentrations of IGF II. Similar findings were noted for the first time in 2 dwarfed adult subjects from the U.S. To determine whether the IGF I deficiency was primary in these patients, we administered human GH (5 mg, twice daily) for 5 days to 11 of the pygmies and the 2 subjects in the U.S. GH-deficient patients and control subjects were studied in a similar manner. At appropriate intervals during treatment, serum urea nitrogen, the serum insulin response to glucose, and, in selected subjects, daily urinary nitrogen, calcium, and phosphate were measured. GH treatment failed to cause a normal increase in IGF I in 9 of 11 pygmy subjects, whereas all GH-deficient subjects had 6–to 10–fold increases in IGF I. GH, likewise, had no effect on IGF I in the 2 subjects from the U.S. with the low IGF I⁄normal IGF II pattern in serum. A significant decrease in the serum urea nitrogen concentration and total urinary nitrogen, a significant increase and a decrease, respectively, in urinary calcium and phosphorus, and significant augmentation of the insulin response to glucose were seen only in subjects with normal or increased IGF I after GH treatment. The combination of normal or increased serum IGF II plus GH given exogenously failed to induce these metabolic changes when IGF I remained low. These data support the hypothesis that a primary deficiency of IGF I is the cause of short staturein the pygmy, and strongly indicate the occurrence of this defect in other ethnic groups. IGF Imay mediate not only the nitrogen-retaining effects of GH, but the insulinotropic and mineralotropic effects as well. (J Clin Endocrinol Metab55:1081, 1982)