REGULATION OF RAT INSULIN-LIKE GROWTH FACTOR-BINDING PROTEIN-1 - THE EFFECT OF INSULIN-INDUCED HYPOGLYCEMIA

Rat insulin-like growth factor-binding protein-1 (rIGFBP-1) was purified from H4IIE rat hepatoma cells by IGF-I affinity chromatography and reverse-phase HPLC. A rabbit antiserum (B2) was raised to rIGFBP-1 and a RIA established. Immunoreactive IGFBP-1 was present in rat amniotic fluid and in the medium conditioned by isolated rat hepatocytes and HTC rat hepatoma cells. To study the effect of hypoglycemia, fasting female Wistar rats were anesthetized and cannulated for multiple venous sampling after the administration of insulin or saline. Serum IGFBP-1 rose in adrenal intact rats from <0.1 mug/ml to a maximum of 1.41 +/- 0.23 mug/ml approximately 120 min after insulin administration. Compared to adrenal-intact rats, adrenalectomized animals demonstrated a delayed rIGFBP-1 response to hypoglycemia and did not appear to have reached a maximum at 180 min. A slow rise in rIGFBP-1 levels throughout the sampling period was seen after saline injection in both adrenal-intact and adrenalectomized animals. Glucose, corticosterone, rat insulin, and human insulin levels were measured and none, alone, appeared responsible for the observed rIGFBP-1 responses. We conclude that 1) rIGFBP-1 is stimulated in response to hypoglycemia in a similar manner to glucose counter-regulatory hormones, 2) an adrenal factor is required for an early rIGFBP1 response to hypoglycemia, and 3) neither circulating glucose nor insulin levels, alone, are responsible for the observed patterns of response.