Intravenous administration of recombinant IGF-I lowers serum GHRH and TSH

Recombinant IGF-I was administered as an iv bolus of 75 μg/kg to 10 patients with Laron type dwarfism and to 8 healthy subjects and determinations of IGF-I, GHRH, hGH, TSH, and glucose were made before and 2, 5, 15, 30, 60, 90, and 120 min. An hypothesis is put forward that acute and time-limited release of somatostatin by IGF-I is the main cause of the hormonal changes registered. As the IGF-I bolus also suppressed circulating insulin levels, the hypoglycemia is considered to be a direct effect of IGF-I