Diabetes, Vol 30, Issue 4 302-309, Copyright © 1981 by American Diabetes Association

ARTICLES

Insulin release in vitro from islet tissues and adenomas of rats treated with nicotinamide and streptozotocin. The effects of glucose

I Frigo, R Younoszai, PK Dixit, SG Matta and GE Bauer

Young male Holtzman rats injected with nicotinamide and streptozotocin develop grossly visible tumors of pancreatic islet tissue. Using an i.v. glucose tolerance test, some tumor-bearing animals exhibited a vigorous (or fast) response to glucose loading (Diabetic Index = 0.47), whereas others showed a subdiabetic (or slow) response (Diabetic Index = 2.34). In vitro perifusion studies demonstrate that tumor pieces from both groups of rats released immunoreactive insulin (IRI) in response to glucose; tumors from fast responding rats showed a rapid monophasic release of IRI (i.e., rapid transient release with little secondary phase), while tumors from slow responders released IRI in a biphasic pattern resembling that of normal islets. A population of large islet masses (or microscopic tumors), isolated from drug-treated rats by collagenase digestion of the pancreas of tumor-containing rats, exhibited glucose-stimulated IRI release that resembled the pattern of the tumor from the same animal. Isolated islets of Langerhans of ordinary size from the pancreas of tumor-bearing rats, on the other hand, usually exhibited a normal (biphasic) IRI release pattern in response to glucose. Analysis by gel filtration suggests that the predominant form of IRI released from perifused tumor preparations, under either basal or glucose-stimulated conditions, eluted at a rate corresponding to rat insulin.
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