Augmented Release of Gastric Inhibitory Polypeptide into the Portal Vein in Response to Intraduodenal Glucose and Amino Acids in Anesthetized Rats Treated with Methylprednisolone or Alloxan

Abstract

Thirty rats were treated with methylprednisolone, 30 rats were treated with alloxan, and 30 control rats were treated with saline alone. The levels of fasting serum insulin and blood glucose and of plasma GIP before and after duodenal instillation of glucose or amino acids were measured using an acute rat preparation that enabled multiple blood samplings from the portal vein. Treatment of the rats with methylprednisolone was followed by increased fasting levels of serum insulin, blood glucose, and plasma GIP and by an augmented GIP release in response to duodenal glucose and amino acids as compared with normal controls. Similarly, treatment with alloxan was followed by decreased fasting levels of serum insulin, by increased fasting levels of blood glucose and plasma GIP, and by an increased GIP release in response to duodenal glucose and amino acids. The augmented GIP release in response to duodenal instillation of glucose and amino acids both in methylprednisolone-treated rats and in alloxan-treated rats may be explained by an increased absorption of these nutrients owing to an increased Na⁺ K⁺ ATPase activity in the intestinal mucosa of corticosteroid- and alloxan-treated rats. The elevated fasting GIP levels, on the other hand, are difficult to explain.

Key-words:

• Alloxan
• amino acid infusion
• diabetes, experimental
• gastric inhibitory polypeptide (GIP)
• glucose, duodenal
• methylprednisolone
• rats