Effect of a glycoprotein biosynthesis-blocker on insulin secretion

The effect of tunicamycin, a glycoprotein biosynthesis-blocker, on insulin secretion was studied using rat isolated pancreatic islets. Islets cultured with tunicamycin during 24 hr released significantly less insulin in response to 11 mM glucose than the corresponding controls. This inhibitory effect of tunicamycin was not significant in the presence of 3.3 mM glucose. The culture of these islets for a second 24 hr period in a medium devoid of tunicamycin did not remove the blocking effect of the drug on the glucose-induced insulin secretion, as demonstrated by measuring the concentration of insulin in the second culture medium or its release during a 60 min incubation period. Fresh isolated islets incubated for 60 min only with tunicamycin also released during this period less insulin in response to 16.6 mM glucose than the corresponding controls. These results might suggest that some islet glycoproteins participate in the mechanism of insulin secretion.