GLUCAGON-SECRETION IN RATS BEARING A GROWTH-HORMONE PRODUCING TUMOR (MTT-W-15)

  • 1 January 1978
    • journal article
    • research article
    • Vol. 4  (4) , 249-253
Abstract
The release of glucagon from pancreatic and extra-pancreatic sources was studied in normal rats and in rats carrying transplants of a MtT-W-15 tumor which secretes large quantities of growth hormone and prolactin. The tumor-bearing rats had high serum levels of A cell immunoreactive glucagon (IRGa), total immunoreactive glucagon (IRGT) and immunoreactive insulin (IRI) and an increased total glucagon and insulin content of the pancreas. Pancreatic islets isolated from tumor-bearing rats secreted more glucagon under basal conditions but did not respond significantly to low glucose stimulation. They contained more insulin per islet and secreted more insulin under basal and stimulated conditions. The serum IRGa response to arginine infusion in vivo was lower in the tumor-bearing than in the normal rats. The introduction of a 5% glucose solution in the small intestine caused similar increases in the serum IRGt level in the 2 groups of rats. The tumor increased the total pancreatic glucagon content and basal secretion, blunted the A cell response to stimulation, but did not significantly alter the secretion of glucagon by the intestine. These responses were attributed to tumor-induced hypersomatotropinism although an effect of the large amounts of circulating prolactin could not be ruled out.

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