PYY (Peptide YY) is a 36-amino acid gut hormone secreted postprandially from enteroendocrine L cells lining the distal small intestine and colon. First isolated from porcine intestine by Adrian et al. in 1985, PYY occupies a critical node in the entero-hypothalamic satiety axis — communicating nutrient status from the gut to appetite-regulating circuits in the brain. Alongside GLP-1 and oxyntomodulin, it forms the triumvirate of L-cell hormones that collectively suppress appetite and reduce energy intake following feeding.
The biologically active form in circulation — PYY3-36 — has attracted intense research interest over the past two decades. Its selective affinity for the Y2 receptor subtype on hypothalamic NPY/AgRP neurons provides a mechanistically distinct satiety signal compared to GLP-1, making it an attractive research target for combination strategies in metabolic research. Landmark work by Batterham et al. in 2003 demonstrated that peripheral infusion of PYY3-36 reduced food intake by approximately 30% in both lean and obese research subjects — placing PYY firmly on the map as a candidate for obesity-related research programs.
This article provides a comprehensive research profile of PYY, covering its molecular biology, receptor pharmacology, central mechanisms of action, role in obesity research, and emerging analog development — all framed for researchers working with this compound in laboratory contexts.
Structure and Molecular Biology
Primary Structure
PYY is a member of the neuropeptide Y (NPY) family, sharing substantial sequence homology with NPY and pancreatic polypeptide (PP). The full-length peptide, PYY1-36, consists of 36 amino acids arranged in a characteristic hairpin-like secondary structure known as the PP-fold — a compact tertiary conformation stabilized by hydrophobic interactions between the N-terminal polyproline helix and the C-terminal amphipathic alpha-helix. The C-terminal tyrosine residue (Tyr-36) is amidated, a post-translational modification essential for full receptor binding activity. The name "PYY" itself derives from the flanking tyrosine (Y) residues at positions 1 and 36 (both single-letter code "Y").
DPP-IV Cleavage and PYY3-36
The primary form secreted by intestinal L cells is PYY1-36. However, this rapidly undergoes N-terminal dipeptide cleavage by dipeptidyl peptidase IV (DPP-IV), the same enzyme responsible for GLP-1 inactivation, generating PYY3-36. In healthy adults, PYY3-36 typically constitutes 40–60% of total circulating immunoreactive PYY in the fasted state and rises as the predominant form after feeding. This proteolytic processing is more than a degradation step — it fundamentally alters receptor binding pharmacology, shifting selectivity from a broad-spectrum Y1/Y2/Y5 profile to highly preferential Y2 receptor engagement.
Receptor Pharmacology
The Y Receptor Family
PYY signals through the neuropeptide Y receptor family, a group of five G protein-coupled receptors (Y1, Y2, Y4, Y5, Y6) that share structural similarity and bind NPY-family peptides with overlapping but distinct selectivity profiles. These receptors canonically couple to inhibitory Gi/o proteins, suppressing adenylyl cyclase activity, reducing intracellular cAMP accumulation, and modulating calcium channels. The downstream effects depend on cell type and receptor subtype, but generally include inhibition of neuronal excitability and neurotransmitter release.
Y2 Selectivity of PYY3-36
The critical pharmacological distinction between PYY1-36 and PYY3-36 lies in their receptor selectivity profiles. PYY1-36 binds Y1, Y2, and Y5 receptors with similar affinity. PYY3-36, lacking the first two N-terminal amino acids, adopts a conformational change that dramatically reduces Y1 and Y5 receptor affinity while preserving or enhancing Y2 binding. This Y2 selectivity is pharmacologically significant because Y2 receptors are expressed presynaptically on NPY-containing neurons in the arcuate nucleus (ARC) of the hypothalamus — the primary appetite-regulating hub. Activation of these presynaptic Y2 receptors suppresses NPY release, thereby relieving tonic inhibition on downstream satiety circuits.
Physiological Secretion and L-Cell Biology
Intestinal L Cells
PYY is co-packaged and co-released with GLP-1 from enteroendocrine L cells — specialized open-type endocrine cells located predominantly in the distal ileum, cecum, and colon, with lower densities in the proximal small intestine. L cells are both mechanosensory and chemosensory: they respond to luminal nutrient presence via direct contact of their apical membrane with intestinal contents, as well as through neural and paracrine signals from neighboring cells.
Stimuli for PYY Release
Postprandial PYY secretion is stimulated by all three macronutrient classes, with fat and protein being the most potent stimuli in most research models. Studies in rodents and humans show that ileal and colonic fat exposure drives the largest PYY increments, consistent with the concept of the "ileal brake" — the physiological mechanism by which distal nutrient delivery slows proximal gastrointestinal motility. Carbohydrate-induced PYY release is generally more modest in controlled research settings. Circulating PYY levels rise within 15 minutes of feeding, peak at 1–2 hours, and remain elevated for up to 6 hours postprandially, providing a prolonged satiety signal relative to the rapidity of GLP-1 secretion and inactivation.
Fasting PYY Levels
Unlike ghrelin, which rises in the fasted state to promote hunger, PYY displays a pulsatile but low basal release profile in the fasted state. The fasting baseline is thought to reflect tonic inhibition of gastric acid secretion and motility — consistent with PYY's original characterization as an "inhibitory peptide" in gastrointestinal physiology research.
Central Mechanisms of Appetite Regulation
Access to the Brain
A key mechanistic question for peripherally released PYY3-36 has been how it communicates with appetite circuits in the central nervous system. Unlike large peptides that are effectively excluded by the blood-brain barrier, PYY3-36 has been shown in rodent research models to access the brain through circumventricular organs — highly vascularized structures lacking a full blood-brain barrier, including the area postrema (AP) and the subfornical organ. The AP, located at the floor of the fourth ventricle in the brainstem, contains dense Y2 receptor expression and projects directly to the nucleus tractus solitarius (NTS), the primary brainstem relay for peripheral satiety signals. Additionally, some research suggests limited direct transcytosis across the choroid plexus, though this remains under investigation.
Hypothalamic Arcuate Nucleus
The arcuate nucleus (ARC) is the primary hypothalamic relay for energy homeostasis signaling. It contains two key neuronal populations with opposing effects: (1) NPY/AgRP neurons, which are orexigenic (appetite-promoting), and (2) POMC/CART neurons, which are anorexigenic (appetite-suppressing). PYY3-36 acts presynaptically on Y2 receptors on NPY/AgRP neurons, suppressing their activity and thereby reducing NPY and AgRP release. This disinhibits POMC neurons, allowing enhanced pro-opiomelanocortin processing and increased melanocortin signaling — a net anorexigenic effect.
This mechanism was elegantly demonstrated in research by Batterham et al. using Y2 receptor knockout mice, which failed to reduce food intake in response to peripheral PYY3-36 injection — confirming Y2-dependent signaling as the essential pathway. Modified PYY molecules engineered for enhanced NPY/AgRP neuron inhibition have been investigated as tools for dissecting the receptor pharmacology of these circuits (PMC6806261).
Brainstem Integration
Beyond the hypothalamus, the brainstem plays a critical integrative role in PYY3-36 satiety signaling. The NTS receives convergent inputs from the vagus nerve (carrying gastric stretch and hormonal signals) and from the area postrema (responding to circulating PYY3-36). NTS neurons project to the hypothalamic paraventricular nucleus (PVN) and lateral hypothalamic area, modulating both autonomic outputs and conscious appetite perception. This dual hypothalamic-brainstem circuitry architecture may explain why PYY3-36 effects in research models persist even when hypothalamic signaling is partially disrupted.
PYY in Obesity Research
Attenuated PYY Release
A consistent finding across multiple research cohorts is that obese individuals display significantly reduced postprandial PYY release compared to lean controls. A key study found that fasting plasma PYY levels were markedly lower in obese subjects, and the postprandial PYY increment was blunted despite caloric intake that would be expected to drive robust L-cell stimulation (PubMed 16166213). This pattern of attenuated gut hormone release in obesity — paralleling similar reductions in postprandial GLP-1 — is thought to contribute to the reduced satiety signaling that characterizes the obese metabolic state.
Resistance vs. Deficiency
An important research distinction is whether obese states are characterized by reduced PYY secretion, impaired PYY responsiveness, or both. The landmark Batterham et al. 2003 NEJM study showed that when PYY3-36 was infused exogenously at matched concentrations, obese subjects reduced food intake comparably to lean subjects — suggesting that peripheral PYY secretion is deficient in obesity, but receptor responsiveness and downstream circuitry remain largely intact (PubMed 12954742). This "secretory deficiency" model has important implications for research strategies aimed at replenishing or augmenting PYY signaling pharmacologically.
Post-Bariatric Surgery Elevations
Research following Roux-en-Y gastric bypass (RYGB) surgery demonstrates marked, sustained increases in postprandial PYY release — typically 3 to 10-fold higher than pre-surgical baselines. These elevated PYY levels are mechanistically linked to accelerated delivery of nutrients to the distal ileum (where L-cell density is highest), bypassing the proximal small intestine. The robust PYY response following RYGB has been proposed as one contributor to the prolonged appetite suppression and food preference changes observed in post-surgical research models, independent of anatomical restriction alone.
PYY and GLP-1 Synergy
Complementary Mechanistic Profiles
PYY3-36 and GLP-1 are co-secreted from the same L cells, yet they operate through distinct and potentially complementary mechanisms. GLP-1 acts primarily through the GLP-1 receptor (GLP-1R) on vagal afferents, brainstem NTS neurons, and hypothalamic arcuate POMC cells, as well as direct effects on pancreatic β-cells. PYY3-36 engages the presynaptic Y2 receptor on NPY/AgRP neurons — a mechanistically non-redundant pathway. This mechanistic complementarity has driven research interest in combined gut hormone strategies.
Additive Anorectic Effects in Research
A notable study by Neary et al. investigated the co-infusion of PYY3-36 and oxyntomodulin (a GLP-1/glucagon receptor co-agonist) in overweight research subjects, finding that combined infusion reduced energy intake by 42.7% compared to saline — significantly greater than either hormone administered alone, which individually reduced intake by approximately 16–17% (PubMed 20357366). This additive effect supports the concept that targeting multiple satiety gut hormones simultaneously may produce synergistic reductions in food intake relevant to metabolic research models.
A 2024 pilot study using both agonists and antagonists of GLP-1 and PYY in diet-induced obese rodents further explored the interaction between these systems, providing mechanistic data on receptor interdependence in obesity models (PubMed 38300808). Reviews of gut hormone physiology consistently identify PYY and GLP-1 as complementary satiety systems warranting co-investigation (PMC3286726).
Long-Acting PYY Analog Development
Engineering Stability and Y2 Selectivity
Native PYY3-36 has a short circulating half-life due to DPP-IV cleavage and renal filtration. Research into long-acting PYY analogs has focused on engineering compounds with extended half-lives through fatty acid conjugation (lipidation), PEGylation, or DPP-IV-resistant N-terminal substitutions — analogous to strategies used in GLP-1 receptor agonist development. Maintaining Y2 receptor selectivity while extending pharmacokinetic duration represents the central structural challenge in this space.
PYY1875 (NN9748) — Novo Nordisk Clinical Program
The most extensively characterized long-acting PYY3-36 analog in recent literature is PYY1875 (also referred to as NN9748), developed by Novo Nordisk. A comprehensive research program spanning preclinical rodent models through Phase 2 human studies was published in 2025. In preclinical research, PYY1875 induced additional body weight reduction in diet-induced obese rodents already treated with semaglutide, demonstrating additive efficacy in animal models. However, the Phase 2 human data showed a modest and not clinically differentiated effect when added to semaglutide 2.4 mg, with the 2.0 mg PYY1875 dose proving poorly tolerated due to gastrointestinal adverse events — a common challenge for gut hormone analogs at doses needed for robust satiety effects (PubMed 40629530). These findings illustrate the translational challenges in PYY analog research and the need for improved formulation strategies.
Research Models and Experimental Approaches
In Vitro and Ex Vivo Systems
Researchers studying PYY biology employ diverse model systems depending on the question of interest. L-cell secretion models include primary intestinal epithelial cultures, GLUTag cells (a murine enteroendocrine L-cell line), and organoid preparations from murine or human intestinal tissue. Y2 receptor pharmacology can be characterized in CHO or HEK293 cells stably transfected with individual Y receptor subtypes, allowing competitive binding assays and downstream signaling measurements. Ex vivo brain slice preparations from the arcuate nucleus or area postrema enable electrophysiological characterization of PYY3-36 effects on identified neuron populations.
In Vivo Rodent Models
PYY3-36 effects on food intake, body weight, and metabolic parameters in rodents have been characterized using peripheral administration (intraperitoneal, subcutaneous, or intravenous infusion) in both acute and chronic paradigms. Diet-induced obesity (DIO) models in C57BL/6 mice and Sprague-Dawley rats represent standard platforms for studying attenuated PYY secretion and exogenous PYY3-36 effects. Y2 receptor knockout mice provide genetic tools for mechanism-of-action confirmation. PYY(3-36) has been shown to reduce food intake and improve insulin sensitivity in rodent DIO models (PubMed 16914421).
PYY vs. Related Peptides in the NPY Family
Comparison with NPY
Neuropeptide Y (NPY) is the most potent known orexigenic peptide, acting primarily through hypothalamic Y1 and Y5 receptors to promote food intake and reduce energy expenditure. PYY3-36 can be conceptualized as a functional counter-regulator of NPY at the presynaptic level — activating Y2 autoreceptors on NPY neurons to suppress NPY release. The same receptor (Y2) that PYY3-36 engages peripherally also functions as an autoreceptor in the CNS, creating a mechanistic feedback loop where gut-derived PYY effectively attenuates centrally-driven hunger. This spatial divergence — peripheral secretion vs. central action — makes PYY research uniquely interesting for understanding gut-brain axis communication, a topic covered further in the Neuropeptide Y research profile.
Comparison with Pancreatic Polypeptide (PP)
Pancreatic polypeptide (PP) is the third member of the NPY-family gut hormones, secreted from PP cells in the pancreatic islets in response to food intake. PP preferentially binds Y4 receptors rather than Y2, mediating distinct effects on gallbladder contraction, pancreatic exocrine secretion, and gastric emptying. Unlike PYY3-36, PP does not appear to directly modulate hypothalamic NPY/AgRP neurons via Y2 receptors, making the mechanistic profile of these related peptides divergent despite structural homology.
Research Considerations and Limitations
Several limitations warrant attention in PYY research. First, species differences in Y receptor distribution and pharmacology mean that rodent findings may not translate directly to primate or human systems — a caution illustrated by the mixed translational record of PYY3-36 analog programs. Second, the temporal dynamics of PYY release are closely intertwined with GLP-1 and other L-cell hormones, making it difficult to isolate PYY-specific contributions without pharmacological or genetic tools. Third, the short half-life of native PYY3-36 in biological matrices requires careful pre-analytical handling (protease inhibitors, immediate plasma separation) to obtain reliable measurements in research settings. Finally, central PYY3-36 vs. peripheral PYY3-36 research questions require careful experimental design, as intracerebroventricular administration does not replicate the physiological route of gut-derived PYY access to brain circuits.
Conclusion and Future Research Directions
PYY (Peptide YY) represents a mechanistically compelling node in the gut-brain satiety axis, operating through a pharmacologically distinct Y2 receptor pathway that is complementary to the GLP-1 and amylin systems. The body of research establishes clear associations between attenuated PYY secretion and obesity, demonstrates robust additive anorectic effects when combined with other gut hormones, and identifies the NPY/AgRP neuron Y2 presynaptic mechanism as a non-redundant satiety target.
The challenges of translating PYY3-36 biology into durable long-acting analogs — illustrated by the tolerability-efficacy trade-offs in the NN9748 program — point toward the need for improved peptide engineering strategies and potentially alternative delivery routes or combination formulations. Emerging research into multi-gut-hormone approaches (combining PYY analogs with GLP-1 and amylin/calcitonin receptor agonists) reflects recognition that obesity involves dysregulation across multiple satiety systems simultaneously.
For researchers, PYY and PYY3-36 remain valuable experimental tools for dissecting hypothalamic and brainstem appetite circuits, characterizing L-cell secretory physiology, and understanding the gut-brain axis in metabolic disease models. All research applications should conform to institutional review board requirements and applicable regulations governing research compound use.
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All content on Peptides.SO is intended for Research Use Only (RUO). Peptide YY and related compounds described in this article are research chemicals intended for in vitro and preclinical laboratory investigation. This content does not constitute medical advice, and these compounds are not approved for human or veterinary use. Researchers must comply with all applicable institutional and regulatory requirements.
References:
1. Batterham RL, et al. "Inhibition of Food Intake in Obese Subjects by Peptide YY3-36." N Engl J Med. 2003;349:941-948. PubMed 12954742
2. Batterham RL, et al. "Attenuated peptide YY release in obese subjects is associated with reduced satiety." Endocrinology. 2006. PubMed 16166213
3. Neary MT, Batterham RL. "The role of peptide YY in appetite regulation and obesity." J Physiol. 2009. PMC2670018
4. Chaudhri OB, et al. "Gut Hormones and Appetite Control: A Focus on PYY and GLP-1 as Therapeutic Targets in Obesity." J Obes. 2012. PMC3286726
5. Pittner RA, et al. "PYY(3-36) reduces food intake and body weight and improves insulin sensitivity in rodent models of diet-induced obesity." Am J Physiol Regul Integr Comp Physiol. 2006. PubMed 16914421
6. Neary MT, et al. "PYY3-36 and oxyntomodulin can be additive in their effect on food intake in overweight and obese humans." Diabetes. 2010;59(7):1635-1640. PubMed 20357366
7. De Silva A, et al. "Modified Peptide YY Molecule Attenuates the Activity of NPY/AgRP Neurons." Endocrinology. 2019. PMC6806261
8. Wulff BS, et al. "Long-acting PYY3-36 analogue with semaglutide for obesity: from preclinical assessment through randomized clinical studies." Obesity. 2025. PubMed 40629530
9. Panaro BL, et al. "GLP-1 and PYY for the treatment of obesity: a pilot study on the use of agonists and antagonists in diet-induced rats." Endocr Connect. 2024. PubMed 38300808
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