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Insulin Secretion and the Morphological and Metabolic Characteristics of Pancreatic Islets of Hyperthyroid ob/ob Mice^*

Institute of Pharmacology and Toxicology, University of Göttingen, Gottingen (S.L.), and Institute of Pathology, University of Hamburg Hamburg (G.K.), Germany

Address requests for reprints to: Dr. Sigurd Lenzen, Institut fur Pharmakologie und Toxikologie, Robert- Koch-Str. 40, D-3400 Gottingen, Germany.

Abstract

Thyroxine treatment induced experimental hyperthyroidism in ob/ob mice, inhibited glucose- induced insulin secretion from the isolated perfused ob/ob mouse pancreas, and reduced total pancreas insulin content. In contrast, glucose-induced insulin release from incubated pancreatic islets and insulin content of pancreatic islets from ob/ob mice isolated by freehand microdissection were not reduced after thyroxine treatment when expressed per µg dry islet. Histological examination of the ob/ob mouse pancreas revealed islets without degenerative lesions of islet cells. Granularity of β cells was well preserved. The average number of pancreatic islets was unchanged. However, the β cell area was significantly decreased in relation to the total pancreatic parenchyma after thyroxine treatment. This implies that insulin release and content per pancreatic islet was half of that of the controls. ATP content of islets was slightly reduced. Glucose oxidation and glucose utilization by islets from treated mice were slightly increased. Thyroxine treatment of the animals did not abolish the stimulation of ⁴⁵Ca²⁺ uptake by glucose, but it did suppress the potentiating effect of fasting on the stimulatory effect of glucose on ⁴⁵Ca²⁺uptake.

The metabolic characteristics of islets from experimentally hyperthyroid mice are those of all hyperthyroid tissues. The results provide no evidence for the view that the effects of thyroxine treatment may be due to disturbed metabolic function or energy deprivation of pancreatic islets. Inhibition of insulin secretion from the pancreas after thyroxine administration is apparently due to a reduction in pancreas insulin content and a diminished pancreatic islet volume. Reduced pancreatic islet volume represents most probably a reduction of individual islet cell volume.

Footnotes

^* This work was supported by the Deutsche Forschungsgemeinschaft (Le 348/2).

Received June 21, 1977.

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