In vivo actions of insulin-like growth factor-I

Abstract

Insulin-like growth factors (IGFs) are structurally, phylogenetically and biologically closely related to insulin (Rinderknecht and Humbel 1978a, 1978b; Zapf et al. 1984). It may, therefore, not appear surprising that intravenous bolus injections of IGF-I or -II into rats cause the same effects as an intravenous injection of insulin (Zapf et al. 1986). In a more spectacular way this comparison has recently been carried out in man (Guler et al. 1987): When a bolus of 100 Hg/kg body wt. of recombinant human IGF-I (rh IGF-I) is administered intravenously to normal human subjects a dramatic fall in the blood sugar is observed (Fig. 1). The lowest blood sugar levels are reached 30 min after the injection. The fall in the blood sugar is accompanied by symptoms of hypoglycemia, i.e., drowsiness, blurred vision, paleness of the face, sweating, trembling, and tachycardia, followed by hunger and fatigue. The hypoglycemic symptoms and the blood sugar curves are identical to those observed during a standard insulin tolerance test with an intravenous injection of 0.15 U/kg body wt. of insulin.