SOMATOSTATIN-STIMULATED INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-1 RELEASE IS ABOLISHED BY HYPERINSULINEMIA

It was demonstrated recently that administration of lanreotide and oct reotide, two somatostatin octapeptide analogs, increased circulating i nsulin-like growth factor binding protein 1 (IGFBP-1) levels. The pres ent study demonstrates that native somatostatin 14 shares this ability and that the increase in abolished by concomitant hyperinsulinemia wi thin the physiological range. Five fasting healthy volunteers underwen t a hyperinsulinemic as well as a normo-insulinemic (i.e. basal insuli nemic) euglycemic clamp lasting 8 h (serum insulin levels remained con stant, about 570 us. 16 pmol/L). Immediately before the clamps, a soma tostatin infusion (500 mu g/h) was started and continued throughout. D uring normo-insulinemia, IGFBP-1 levels increased slowly from 6.3 +/- 6.2 to 36.1 +/- 14.8 mu g/L (P < 0.05) reaching maximum after 7 h cons tant somatostatin infusion, whereas hyperinsulinemia induced a signifi cant decrease from basal levels (from 4.7 +/- 5.4 to 1.1 +/- 1.5 mu g/ L) after 8 h (mean +/- so, n = 5). These results may indicate hitherto unnoticed interactions of somatostatin and insulin on IGFBP-1 release with possible impact on IGF-I action at the cellular level.