Normal insulin sensitivity during the phase of glucose intolerance but insulin resistance at the onset of diabetes in the spontaneously diabetic BB rat.

In diabetes-prone BB rats, 30 to 50% of animals undergo autoimmune destruction of the pancreatic B-cells leading to a short period of glucose intolerance, followed by an abrupt onset of diabetes. We have examined whether the glucose intolerance period and the onset of diabetes are associated with changes in insulin sensitivity, using the euglycaemic hyperinsulinaemic clamp coupled with [3-3H] glucose infusion. Glucose intolerant rats were detected by a transient glycosuria one hour after an oral glucose load performed every four days. Insulin sensitivity studied in these rats the day following their detection was normal. Other diabetes-prone BB rats were tested daily and studied on the first day of glycosuria. In the basal state, glucose production was increased in diabetic rats (11.3 +/- 1.1 vs 7.1 +/- 0.8 mg.min-1.kg-1, p less than 0.05). Tissue glucose utilization was similar in diabetic and control rats (8.3 +/- 0.5 vs 7.1 +/- 0.8 mg.min-1.kg-1) despite a three fold higher glycaemia in the diabetic rats. During the hyperinsulinaemic clamps, glycaemia was clamped at 6.1-6.6 mmol/l in diabetic and control rats. A decreased insulin sensitivity was observed in diabetic rats at submaximal (200 microU/ml) and maximal (1500 microU/ml) insulin concentrations for both inhibition of hepatic glucose production and stimulation of glucose utilization. No autoantibodies against insulin could be detected in the plasma of diabetic rats. Plasma concentrations of glucagon, catecholamines, ketone bodies and fatty acids were similar in control and diabetic rats during the clamp studies.(ABSTRACT TRUNCATED AT 250 WORDS)