Lack of effect of calcium infusion on blood glucose and plasma insulin levels in patients with insulinoma.

In vitro calcium plays a fundamental role in regulating insulin secretion. On the other hand, the influence of calcium excess on insulin release in vivo is not clearly defined. Recently, calcium infusion has been proposed as a provocative test for the diagnosis of insulin-secreting tumors. A 2-h infusion of calcium gluconate was performed (4 mg/kg . h) in six patients with islet cell adenoma. As a result, mean calcium plasma levels increased from 9.6 +/- 0.4 to 11.6 +/- 0.8 mg/100 ml. During calcium infusion, blood glucose and plasma insulin concentrations remained unchanged. These observations suggest that calcium fails to stimulate basal insulin secretion even in cases of organic hyperinsulinism. They show that calcium infusion is not helpful as a provocative test in the diagnosis of insulinoma.