Main function of GTR is/are:
**Core Concept:** Glucagon-like peptide-1 (GLP-1) is an incretin hormone secreted by L cells in the gastrointestinal tract in response to food intake, primarily glucose. GLP-1 stimulates insulin secretion in a glucose-dependent manner and inhibits glucagon secretion, gastric emptying, and pancreatic beta cell proliferation. GTR (Glucagon-like peptide-1 receptor agonist) is a class of drugs that mimic the effects of GLP-1, targeting the GLP-1 receptor.
**Why the Correct Answer is Right:** The correct answer is D. **Glucagon-like peptide-1 receptor agonist (GLP-1 RA)**. This is because the main function of GTR is to stimulate insulin secretion in a glucose-dependent manner and inhibit glucagon secretion, thereby aiding in glycemic control in patients with type 2 diabetes mellitus (T2DM). GLP-1 RAs mimic the effects of GLP-1, binding to the GLP-1 receptor on pancreatic beta cells to achieve these actions.
**Why Each Wrong Option is Incorrect:**
A. **Glucose tolerance test (GTT)**: A GTT is a diagnostic test used to evaluate glucose tolerance. While GTRs can improve glucose tolerance, the core function of a GTT is not drug therapy for T2DM.
B. **Incretin hormones**: GLP-1 is an incretin hormone, one of the three main incretin hormones (GLP-1, GIP, and GLP-2). While incretin hormones play a role in glucose regulation, the specific function of GTR is targeting GLP-1 receptor.
C. **Insulin and glucagon secretion**: GTRs do influence insulin and glucagon secretion, but the primary focus of GTRs is on the GLP-1 receptor, which is not directly related to these hormones' secretion but rather the downstream effects mediated by the GLP-1 receptor on beta cells.
E. **Glucose-dependent insulin secretion**: While GLP-1 and GTRs (D) do stimulate glucose-dependent insulin secretion, the focus on GLP-1 receptor agonism is more relevant, as it is the receptor activation that leads to glucose-dependent insulin secretion rather than the hormone itself.
**Clinical Pearl:** In clinical practice, GLP-1 RAs are a class of drugs used as an oral or injectable therapy for T2DM, demonstrating the importance of understanding the specific target receptor for these drugs.