Insulin hypoglycaemia test guided by a glucose controlled insulin infusion system

Insulin hypoglycaemia test (IHT) for assessment of hypothalamic-pituitary-adrenocortical (HPA) function in patients with pituitary tumours is usually performed by bolus injection of insulin, a procedure which includes the risk of overdosage and/or the need of repeated administration. This study describes that a glucose controlled insulin infusion system (GCIIS) permits to perform the IHT with standardized hypoglycaemia. Ten healthy volunteers and 10 patients with pituitary tumours were studied using the GCIIS (Biostator) on static control (Mode 1:1, BI 35, QI 10, RI 20, FI 300). Insulin administration was discontinued and the GCIIS used only for monitoring of blood glucose (BG), when BG had fallen below 40 mg/dl and initial clinical symptoms for hypoglycaemia were observed. In controls, the GCIIS guided IHT achieved a sufficient degree of hypoglycaemia (BG 27.6 +/- 2.0 mg/dl; mean +/- SEM) and physiological responses for GH (peak 49.4 +/- 6.7 ng/ml), Prl (peak 1766 +/- 614 microU/ml), ACTH (peak 76.0 +/- 8.7 pg/ml) and cortisol (peak 252 +/- 15 ng/ml). The total amount of insulin given was 0.115 +/- 0.012 U/kg. In the patients with pituitary tumours however, the required insulin dose varied markedly from 0.090 (pituitary insufficiency) to 0.340 U/kg (Cushing's syndrome). Minimum BG obtained was 32.5 +/- 1.9 mg/dl. Partial impairment of hypothalamic-pituitary function and, in particular, patients requiring exogenous cortisol supplementation during stress, could be identified. In conclusion, special advantages of the GCIIS-guided IHT are: Optimal insulin dosage with standardized hypoglycaemia due to automatic adjustment to the individual insulin sensitivity.(ABSTRACT TRUNCATED AT 250 WORDS)