Glucose intolerance in the carcinoid syndrome

Area of Science:

• Endocrinology
• Oncology
• Metabolic Research

Background:

• Carcinoid syndrome, often associated with metastatic carcinoid tumors, presents with elevated serotonin levels.
• Glucose intolerance and impaired insulin secretion are potential complications in patients with carcinoid syndrome.

Purpose of the Study:

• To investigate glucose tolerance and insulin secretion in patients with active carcinoid syndrome versus those with inactive tumors.
• To determine the role of serotonin in the metabolic alterations observed in carcinoid syndrome.

Main Methods:

• Assayed glucose tolerance and insulin secretion using intravenous glucose disposal rate constants (KG) and insulinogenic index.
• Administered serotonin antagonist cyproheptadine and serotonin synthesis inhibitor p-chlorophenylalanine to assess their effects.
• Evaluated the impact of streptozotocin treatment on glucose metabolism and insulin secretion.

Main Results:

• Patients with active carcinoid syndrome showed significantly lower KG values and impaired insulin secretion compared to normals.
• Serotonin antagonism and synthesis inhibition partially improved glucose disposal and insulin secretion.
• Insulin half-life was normal, suggesting impaired secretion, not accelerated destruction, as the cause of low insulin levels.

Conclusions:

• A high incidence (80%) of glucose intolerance and impaired insulin secretion occurs in carcinoid syndrome.
• Serotonin plays a significant role in causing these glucose metabolism and insulin secretion abnormalities.
• Streptozotocin treatment did not impair glucose tolerance or insulin secretion in the studied patients.