Early paradoxical decrease in serum somatomedin activity following injection of growth hormone.

The early effects have been investigated of an intra-muscular growth hormone injection (6 mg/m2) on serum somatomedin activity in 21 children with growth hormone deficiency and in 5 children with constitutional short stature. In cases of hGH total deficiency, there was an early and significant decrease in SM activity, which reached a minimum level 2 hours after the injection (-34% p less than 0.01). After 24 hours, SM activity increased to +64% above basal levels. In cases of hGH partial deficiency and in short, non-hGH deficient children, no similar early changes were observed. Neither was any correlation found between the variations in SM activity and those in hGH or free fatty acid levels. The unexpected early decrease in SM activity following hGH administration seems to be related to GH deficiency.