**Question:** Which of the following drugs promotes the release of endogenous insulin?

A. Insulin
B. Glucagon
C. Glucose
D. Glucose tolerance test

**Core Concept:**
Insulin and glucagon are two key hormones involved in maintaining blood glucose homeostasis. Insulin is secreted by beta cells of the pancreas, while glucagon is secreted by alpha cells. Both hormones have opposing effects on blood glucose levels. Insulin lowers blood glucose by promoting glucose uptake into cells, while glucagon increases blood glucose by stimulating glycogenolysis and gluconeogenesis in the liver.

**Why the Correct Answer is Right:**
The correct answer, **B. Glucagon**, promotes the release of endogenous insulin because glucagon is the hormone that opposes insulin's effects. When blood glucose levels rise, such as after a meal, glucagon is secreted by the alpha cells of the pancreas to counteract insulin's actions. Glucagon stimulates glycogenolysis (breakdown of glycogen to glucose) and gluconeogenesis (conversion of non-carbohydrate precursors into glucose) in the liver, increasing blood glucose levels and thereby counteracting the hypoglycemic effect of insulin.

**Why Each Wrong Option is Incorrect:**
A. Insulin is the hormone that lowers blood glucose levels by promoting glucose uptake into cells, not promoting the release of endogenous insulin.
C. Glucose itself does not directly promote the release of endogenous insulin; rather, it stimulates insulin secretion by the beta cells in response to high blood glucose levels.
D. A glucose tolerance test involves administering a glucose load to assess an individual's insulin and glucagon responses, not promoting the release of endogenous insulin.

**Clinical Pearl:**
Understanding the interplay between insulin and glucagon is essential for managing blood glucose levels in patients with diabetes mellitus. In type 1 diabetes, patients lack insulin production, while in type 2 diabetes, insulin resistance leads to insufficient insulin action. Appropriate treatment involves both oral hypoglycemic agents and insulin therapy to mimic the actions of insulin and glucagon, respectively. This helps maintain blood glucose levels within a normal range, preventing diabetic complications.