The regulation of metabolism relies on a complex network of peptide hormones that coordinate communication between the gut, pancreas, liver, brain, and other tissues (Holst; Drucker). Among the most important are glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and glucagon. Although each hormone has distinct physiological functions, they work together to help maintain glucose homeostasis, regulate nutrient utilization, and adapt the body's metabolic response following food intake (Alfaris et al.; Goldney et al.).
In recent years, these hormones have gained significant attention in peptide research as scientists increasingly recognize that metabolism is controlled through multiple interconnected signaling pathways rather than a single receptor (Alfaris et al.). This understanding has influenced the development of investigational peptides designed to engage one or more of these pathways simultaneously, making GLP-1, GIP, and glucagon central to modern metabolic peptide research (Goldney et al.).
This article explores the biology of these three hormones, how their signaling pathways differ, and why their coordinated actions have become an important focus in the development of next-generation peptide therapies.
What Are GLP-1, GIP, and Glucagon?
GLP-1, GIP, and glucagon are naturally occurring peptide hormones that regulate different aspects of metabolism (Holst; Wolfe et al.; Kajani et al.). While they are often discussed individually, their biological functions are closely interconnected, coordinating how the body responds to changes in nutrient availability through glucose regulation, digestive processes, energy balance, and communication between multiple organs (Alfaris et al.).
GLP-1
Glucagon-like peptide-1 (GLP-1) is an incretin hormone produced primarily by L cells located in the distal small intestine and colon following food intake (Holst). After binding to the GLP-1 receptor, it enhances glucose-dependent insulin secretion, suppresses glucagon release under certain conditions, slows gastric emptying, and contributes to satiety through signalling within the central nervous system (Holst; Drucker; Cabou & Burcelin). Native GLP-1 has a very short circulating half-life because it is rapidly degraded by the enzyme dipeptidyl peptidase-4 (DPP-4) (Holst; Madsbad).
GIP
Glucose-dependent insulinotropic polypeptide (GIP) is another incretin hormone, secreted by K cells in the upper small intestine shortly after nutrients enter the digestive tract (Wolfe et al.). Like GLP-1, GIP enhances glucose-dependent insulin secretion by activating the GIP receptor on pancreatic β-cells and accounts for approximately 60–80% of the postprandial insulin response under normal conditions (Wolfe et al.). In addition to its effects on glucose regulation, GIP signalling is investigated for its role in lipid metabolism, adipose tissue biology, and energy homeostasis (Wolfe et al.).
Glucagon
Unlike GLP-1 and GIP, glucagon is produced by α-cells within the pancreas (Kajani et al.). It plays a central role during fasting by stimulating glucose production in the liver, helping maintain blood glucose concentrations when dietary nutrients are unavailable (Kajani et al.). Beyond glucose regulation, glucagon also influences amino acid metabolism and energy expenditure, making it an important component of the body's broader metabolic response (Kajani et al.).
Coordinated Hormonal Responses to Nutrient Intake
Although GLP-1, GIP, and glucagon each have distinct physiological functions, they operate as part of an integrated hormonal network rather than acting independently (Holst; Wolfe et al.). Their secretion and activity are continuously adjusted according to nutrient availability, allowing the body to maintain glucose homeostasis, regulate energy utilization, and coordinate communication between multiple organs (Alfaris et al.; Kajani et al.).
Incretin Signaling Following Food Intake
Following food intake, nutrients entering the small intestine stimulate the release of both GLP-1 and GIP from specialized enteroendocrine cells (Holst; Wolfe et al.). These hormones, collectively known as incretins, enhance glucose-dependent insulin secretion from pancreatic β-cells, ensuring that insulin release closely matches the rise in blood glucose concentrations (Holst; Wolfe et al.).
GLP-1 also suppresses glucagon secretion when blood glucose levels are elevated, reducing unnecessary glucose production by the liver (Holst; Drucker). Together, GLP-1 and GIP contribute to the efficient processing, storage, and utilization of nutrients while helping maintain stable blood glucose levels after meals (Wolfe et al.; Madsbad).
Metabolic Regulation During Fasting
As nutrient absorption declines between meals, the body's metabolic priorities shift. During this period, pancreatic α-cells increase glucagon secretion, stimulating the liver to release stored glucose and produce additional glucose through gluconeogenesis (Kajani et al.). This response helps maintain a continuous energy supply for tissues that depend on glucose, particularly the brain. In this way, glucagon complements the actions of insulin by helping maintain blood glucose concentrations between meals and during periods of fasting (Kajani et al.).
Systemic Actions Beyond Glucose Homeostasis
The biological functions of GLP-1, GIP, and glucagon extend well beyond glucose regulation (Drucker; Wolfe et al.; Kajani et al.). GLP-1 contributes to satiety by acting on regions of the central nervous system involved in appetite regulation and slows gastric emptying, influencing the rate at which nutrients enter the circulation (Holst; Cabou & Burcelin). GIP participates in communication between the gut, pancreas, adipose tissue, and bone, with ongoing research investigating its broader role in energy homeostasis (Wolfe et al.). Glucagon influences hepatic metabolism, amino acid turnover, and energy expenditure, demonstrating that its physiological functions extend beyond stimulating glucose production during fasting (Kajani et al.).
Implications for Metabolic Peptide Research
The growing understanding of how GLP-1, GIP, and glucagon interact has reshaped metabolic peptide research (Alfaris et al.; Goldney et al.). Rather than viewing these hormones as isolated signaling pathways, researchers increasingly recognize them as components of an integrated physiological network that regulates metabolism through complementary mechanisms (Holst; Kajani et al.).
This growing understanding of hormone biology has influenced how researchers approach metabolic peptide design (Alfaris et al.). Rather than focusing on individual signaling pathways, current research increasingly explores how multiple receptors can be activated to better reflect the coordinated physiological responses observed in the body (Goldney et al.; Wolfe et al.).
Peptides Targeting GLP-1, GIP, and Glucagon Signaling
As researchers gained a deeper understanding of GLP-1, GIP, and glucagon physiology, peptide engineering evolved beyond targeting individual receptors (Alfaris et al.; Goldney et al.). Rather than replicating the actions of a single hormone, newer investigational peptides increasingly combine complementary signaling pathways to better reflect the coordinated metabolic responses that occur naturally following nutrient intake (Alfaris et al.).
This progression has led from selective GLP-1 receptor agonists to dual- and triple-receptor agonists, each representing a different strategy for studying metabolic regulation (Goldney et al.).
Peptides Targeting GLP-1 Signaling: Semaglutide, Liraglutide, and Exenatide
The first generation of metabolic peptides was designed to selectively activate the GLP-1 receptor while overcoming the rapid degradation of native GLP-1 (Drucker; Knudsen & Lau). Examples include semaglutide, liraglutide, and exenatide, which mimic many of the physiological actions of endogenous GLP-1 but have been engineered to remain active in circulation for longer periods (Madsbad; Lau et al.).
These peptides established the foundation for modern metabolic peptide research by demonstrating the potential of selectively targeting GLP-1 signaling (Drucker).
Peptides Targeting GLP-1 and GIP Signaling: Tirzepatide
As understanding of incretin biology expanded, researchers began exploring whether activating both GLP-1 and GIP receptors could more closely reproduce the coordinated hormonal responses that occur after food intake (Wolfe et al.). Tirzepatide became the first widely studied peptide to combine these two pathways within a single molecule, reflecting the complementary roles of GLP-1 and GIP in metabolic regulation (Frías et al.; Gallwitz).
Peptides Targeting GLP-1 and Glucagon Signaling: Mazdutide and Survodutide
Another area of investigation has focused on combining GLP-1 receptor activation with glucagon receptor signaling (Kajani et al.). Mazdutide and survodutide are examples of investigational peptides developed using this approach. Rather than targeting incretin pathways alone, these molecules explore how glucagon signaling may complement GLP-1 through its effects on hepatic metabolism and energy expenditure (Ji et al.; le Roux et al.).
Peptides Targeting GLP-1, GIP, and Glucagon Signaling: Retatrutide
The latest stage in this progression includes peptides capable of activating all three metabolic hormone receptors simultaneously (Goldney et al.). Retatrutide is an example of a triple-receptor agonist that targets GLP-1, GIP, and glucagon receptors within a single molecule. This approach reflects the growing recognition that metabolism is regulated through multiple interconnected signaling pathways rather than by individual hormones acting in isolation (Jastreboff et al.; Rosenstock et al.).
Did You Know?
Retatrutide is sometimes referred to as "GLP-3," but this isn't an official scientific name (Jastreboff et al.).
The nickname comes from retatrutide's ability to activate three metabolic hormone receptors: the GLP-1 receptor, GIP receptor, and glucagon receptor (Jastreboff et al.; Rosenstock et al.). While the term "GLP-3" highlights its triple-receptor mechanism, retatrutide is not a naturally occurring hormone and does not belong to a distinct "GLP-3" hormone family. In the scientific literature, it is more accurately described as a triple-receptor agonist or triagonist (Goldney et al.; Alfaris et al.).
The evolution from single-receptor agonists to multi-receptor peptides reflects a broader shift in metabolic peptide research (Alfaris et al.; Goldney et al.). Instead of focusing on one hormone at a time, researchers increasingly investigate how combinations of signaling pathways can better represent the complexity of human metabolism (Holst; Kajani et al.). Understanding the physiological roles of GLP-1, GIP, and glucagon therefore provides important context for interpreting the rationale behind these investigational peptide designs (Wolfe et al.; Alfaris et al.).
Comparing GLP-1, GIP, and Glucagon
Although GLP-1, GIP, and glucagon all contribute to metabolic regulation, each hormone has a distinct physiological role (Holst; Wolfe et al.; Kajani et al.). They differ in their site of production, receptor distribution, and primary biological functions, yet together they form an integrated signaling network that helps maintain metabolic homeostasis (Alfaris et al.; Drucker).
*Some investigational peptides activate more than one receptor and therefore appear in multiple categories.
Although GLP-1 and GIP are both classified as incretin hormones, they are not interchangeable. They are released from different enteroendocrine cells, bind to distinct receptors, and contribute to metabolic regulation through complementary physiological mechanisms. Glucagon, meanwhile, serves a different role by helping maintain glucose availability during fasting and supporting broader aspects of energy metabolism.
Where to Get Research Peptides Targeting GLP-1, GIP, and Glucagon Signaling
When sourcing research peptides that target GLP-1, GIP, or glucagon signaling, product quality and analytical verification are critical. Because these compounds are used in laboratory research, investigators should look for suppliers that manufacture under recognized quality standards, provide independent analytical testing, and maintain appropriate storage and shipping conditions to preserve peptide integrity.
Vera is one supplier specializing in high-quality metabolic research peptides. Products are manufactured in GMP-certified facilities, undergo independent third-party testing, and are supplied with a Certificate of Analysis (COA)verifying identity and purity. Temperature-controlled shipping further helps maintain peptide stability throughout transport, supporting consistent research outcomes.
Polaris also offers a broad portfolio of research peptides, including compounds targeting GLP-1, GIP, and glucagon signaling pathways. The platform provides access to both established and emerging investigational peptides, making it another valuable resource for researchers working in metabolic peptide science.
Conclusion
GLP-1, GIP, and glucagon each play distinct roles in metabolic regulation, yet their physiological functions are closely interconnected. Rather than acting as isolated hormones, they coordinate communication between the gut, pancreas, liver, brain, and other tissues to maintain glucose homeostasis, energy balance, and nutrient utilization. Understanding how these pathways interact provides a more complete picture of metabolic physiology than considering each hormone individually.
This growing understanding has also shaped the direction of peptide research. As investigators continue to explore increasingly sophisticated receptor combinations, the coordinated biology of GLP-1, GIP, and glucagon remains the foundation upon which modern metabolic peptide engineering is built.
