Effect of vinblastine in vivo on ultrastructure and insulin releasing capacity of the B-cell following sulphonylurea and isopropyl-noradrenaline.

The effect of vinblastine in vivo on ultrastructure and insulin releasing capacity of the B-cell was studied in mice. Treatment with vinblastine (1.1 mumole/mouse) resulted in a 75% decrease of the amount of normal microtubules and the appearance of characteristic paracrystals. Basal plasma immunoreactive insulin levels were depressed to about 60% of the control level. The dose-response pattern for insulin release (first phase) following two chemically unrelated insulin secretagogues, the potent sulphonyl-urea derivative, glibenclamide, and the beta-adrenegic agonist L-isopropylnoradrenaline, (L-IPNA), was tested with and without vinblastine pretreatment. The dose-response curves for L-IPNA-induced insulin release in vinblastine-treated and control animals did not deviate significantly from each other, whereas insulin release following glibenclamide was almost totally suppressed by vinblastine except at the lowest dose level. Injection of maximal doses of glibenclamide or L-IPNA did not alter the ultrastructural changes induced by vinblastine in the B-cells. It is suggested that the microtubular system of the B-cell might play a minor role for certain insulin-releasing processes and/or that vinblastine might have other important effects on the insulin secretory machinery.