Effects of insulin per se on neuroendocrine and metabolic counter-regulatory responses to hypoglycaemia.

We examined and compared findings from studies aimed at detecting and quantifying an effect of insulin per se on counter-regulatory responses to hypoglycaemia. The experimental protocols used in many of these studies were very different with regard to study design and patient population, resulting at times in inconsistencies and discrepancies. Taken together, the results from this extensive body of work clearly indicate that, at similar levels of hypoglycaemia, greater hyperinsulinaemia results in enhanced counter-regulatory responses. This enhancement includes higher circulating levels of counter-regulatory hormones (adrenaline, noradrenaline, cortisol and growth hormone, but not glucagon), more intense activation of hypoglycaemic symptoms (both neural-sympathetic and adrenal-sympathetic), and greater deterioration of neuropsychological skills. The insulin-induced enhancement of counter-regulatory responses is not influenced by gender, is present in several animal species, and applies to healthy subjects as well as to patients with Type I diabetes. The underlying mechanisms remain speculative, and possibly include a direct neuromodulatory effect and/or suppression of glucose utilization in various areas of the brain, which either independently or in a hierarchical fashion trigger the sequence of downstream counter-regulatory events.