Abstract
Plasma immunoreactive insulin levels following the intravenous injection of glucose (IVGTT) were determined in 38 individuals classified as 10 normal subjects, 19 patients with mild glucose intolerance, 12 moderate diabetics, and 4 severe diabetics.
All the subjects were previously divided into one of the four groups by a 50g oral glucose tolerance test.
The plasma insulin response to IVGTT was lowered in all diabetic groups. In patients with glucose intolerance, plasma insulin levels in the early phase of IVGTT were significantly lowered in comparison with normal subjects (p<0.01).
In order to investigate the effects of drugs on the low plasma insulin response to IVGTT in patients with mild glucose intolerance, or moderate diabetes plasma insulin levels following IVGTT were determined during the intravenous infusion of such as aminophylline, tolbutamide, isoproterenol, phentolamine, glucagon and arginine.
In these experiments, the test substances were infused for 60 minutes, and 25g of glucose was injected 50 minutes after the start of the infusion of drugs.
Results are summarized as follows.
1. The plasma insulin concentration did not increase during the intravenous infusion of aminophylline (500mg), but plasma insulin response to IVGTT was slightly improved by aminophylline (p<0.05).
2. During the intravenous infusion of tolbutamide (0.1g), isoproterenol (0.2mg), and phentolamine (30mg), plasma insulin concentration was found to be increased, and, furthermore, the plasma insulin response to IVGTT was significantly improved (p<0.05).
3. Following the intravenous infusion of glucagon (0.5 mg), significantly increased plasma insulin levels and improved plasma insulin response to IVGTT were observed (p<0.05). However, blood glucose levels markedly increased in this experiment.
4. The intravenous infusion of arginine (30g) not only markedly increased the plasma insulin concentration, but it also improved the plasma insulin response to glucose significantly (p<0.01).
These results suggest that such drugs as tolbutamide, aminophylline, isoproterenol, phentolamine, and glucagon, which increase intracellular cyclic AMP levels, and amino acids, improved early insulin response to intravenous glucose load in low insulin responders.
