Evidence That the Beta Cell Microtubules Are Not Involved in Arginine-Induced Insulin Release

Abstract

The role of the beta cell microtubules in stimulus-induced insulin release was evaluated in the intact rat by utilizing vincristine, a known microtubular disrupting agent. In the first study, pancreases were removed at 60 min after vincristine (0.5 mg/kg) or vehicle (control) treatment for electron microscopy. Morphometric analysis revealed that the number of microtubules in the vincristine-treated rat pancreases was significantly less than that observed in the control rat pancreases. In the next series of studies, insulin release in response to a glucose (150 mg, iv) or an arginine (100 mg/kg, iv) pulse was examined at 60 min after vincristine (0.5 mg/kg) or vehicle treatment. In response to glucose, insulin release at 2, 3, and 5 min was significantly less, and glucose tolerance was significantly impaired in the vincristine-treated rats as compared with those observed in the control rats. In contrast, insulin release in response to arginine was similar in the vincristine-treated and the control rats. Therefore, a marked morphological alteration of the beta cell microtubules has failed to inhibit arginine-induced insulin release in the intact rat. These findings suggest that the integrity of microtubules may not be critical in the process of arginine-induced insulin release.