Dynamics of Insulin Release and Microtubular‐Microfilamentous System

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Abstract
The effect of colchicine upon glucose‐induced insulin release by the isolated perfused rat pancreas was examined in order to characterize the participation of the β‐cell microtubular apparatus in the biphasic insulin secretory response to glucose. After a short pretreatment (25 min.) with a low colchicine concentration (2.10−5 M), both the early and late phases of glucose‐induced insulin secretion were markedly enhanced. As either the concentration of colchicine or the length of the pretreatment period with this mitotic spindle‐inhibitor were increased, the facilitating effect faded out and partial inhibition of insulin release was observed. However, colchicine, even at high concentration, markedly enhanced the residual early release of insulin evoked by glucose in the presence of diazoxide (0.05 mg/ml). These findings suggest that (i) a fraction of the early phase of insulin secretion completely escapes from the inhibitory effect of colchicine and may correspond, therefore, to a modality of hormonal release which does not involve the oriented intracellular translocation of secretory granules; and (ii) extensive disruption of the microtubular apparatus is associated with inhibition of insulin release, especially during the late phase of the secretory response to glucose.