Although intraislet insulin signaling is known to play a critical role in regulating glucagon secretion, it is unknown whether abnormal glucagon secretion influences the hypoglycemic effect of exogenous insulin with intraislet insulin deletion. We performed a longitudinal study using 16 streptozocin (STZ)-induced diabetic rhesus monkeys to explore α-cell function under the absence β-cells and to assess whether increasing glucagon secretion antagonizes the action of exogenous insulin for glycemic control. We found that although the α-cells were impaired and the basal secretion levels of glucagon decreased rapidly after STZ (80-90 mg/kg) administration, as based on long-term observation post-STZ injection, glucagon secretion and the number of α-cells were increased. Glycemic control was increasingly difficult, the insulin resistance (HOMA-IR) index was significantly higher, and the triglycerides (TG) levels were gradually decreased. Moreover, a significant correlation between the levels of glucagon and HOMA-IR was found. Under the long-term absence of β-cells, the inhibitory effect on α-cell activity is profoundly attenuated, leading to an increase in glucagon secretion and the amount of α-cells and even α-cell dysfunction. Increased glucagon levels have a serious impact on the insulin sensitivity in vivo and result in an antagonization of the hypoglycemic effect of exogenous insulin.
Keywords: diabetic rhesus monkeys; exogenous insulin; glycemic control; insulin sensitivity; α-cell dysfunction.