SUMMARY

Pancreatic β-cell responses to a controlled intravenous glucose stimulus in 18 untreated non-insulin-dependent diabetic patients were compared with those in seven healthy control subjects. The patients' first- and second-phase responses were only 10 to 20 per cent of those of the normal subjects. However, when normal subjects had been hyperglycaemic for two hours, their first-phase responses were similar to those of the patients. Six patients were subsequently treated by diet alone, six by diet and tolbutamide and six by diet and metformin. There was no improvement in first-phase responses after treatment, but second-phase responses doubled. Improved responses were seen with all treatments, and correlated with the fall in fasting blood glucose concentration during treatment. This study supports the view that hyperglycaemia impairs β-cell function and suggests that first-phase responses are more sensitive to hyperglycaemia than second-phase responses.