Plasma insulin disturbances in primary hyperparathyroidism.

Area of Science:

• Endocrinology
• Metabolic Research
• Calcium Homeostasis

Background:

• Primary hyperparathyroidism is associated with elevated calcium levels (hypercalcemia).
• The impact of hypercalcemia on insulin secretion and glucose metabolism requires further elucidation.

Purpose of the Study:

• To investigate plasma insulin dynamics in patients with primary hyperparathyroidism before and after parathyroidectomy.
• To determine the effects of induced hypercalcemia on insulin secretion and glucose tolerance in healthy individuals.

Main Methods:

• Evaluated plasma insulin and glucose levels in 10 hyperparathyroid patients pre- and post-surgery.
• Administered glucose, tolbutamide, and glucagon challenges.
• Induced hypercalcemia in normal subjects via parathormone injections and calcium infusions.
• Incubated parathormone with isolated rat pancreatic islets.

Main Results:

• Patients with hyperparathyroidism exhibited higher fasting insulin and augmented insulin responses to glucose, tolbutamide, and glucagon pre-surgery compared to post-surgery.
• Hypercalcemia in normal subjects did not alter glucose tolerance but enhanced insulin response to tolbutamide, potentiating its hypoglycemic effect.
• Parathormone incubation with rat islets did not affect glucose-stimulated insulin secretion.

Conclusions:

• Chronic hypercalcemia in hyperparathyroidism induces insulin resistance, necessitating compensatory hyperinsulinemia for glucose homeostasis.
• Hypercalcemia selectively enhances pancreatic beta-cell responsiveness to tolbutamide, leading to hypoglycemia.
• The direct role of parathormone in these observed effects remains undetermined.