Immunoreactive insulin and insulin degrading enzymes in erythrocytes. A preliminary report

Immunoreactive insulin (IRI) and insulin degrading enzyme activity (IDEA) of the plasma and the corresponding erythrocyte lysate were estimated in 21 normal volunteers, 18 non insulin dependent diabetic patients (NIDDM), and 16 insulin dependent diabetics (IDDM). The erythrocytes contained several-fold higher concentrations of IRI than in plasma, both in normal and diabetic subjects. The values in controls ranged from 80 to 458 uU/ml against a range of 5 to 25 uU/ml in the corresponding plasma samples. The IRI contents of the diabetic patients were also similar. It showed no correlation to the fasting plasma glucose or the plasma IRI. Following an oral glucose load, no change occurred in the IRI content of the erythrocytes, unlike the changes seen in plasma. The IRI content of the lysate increased with dilution of the sample. The IDEA was higher in diabetic patients compared to controls, especially so in the IDDM (P less than 0.01). It also showed more than one peak activity at different pH of the reaction buffer, indicating the possibility of a complex of enzymes. Human erythrocytes contain large pools of IRI and its degrading enzymes. The significance of the pool of the insulin in non-target tissue needs to be studied.