Mechanism of Action
Y2 Receptor Inhibition of NPY Neurons
PYY3-36 crosses the blood-brain barrier and binds Y2 receptors (Gi-coupled) on NPY/AgRP neurons in the arcuate nucleus, acting as autoreceptors that inhibit NPY release. This removes the orexigenic NPY drive, reducing appetite. Y2 activation also reduces NPY release from sympathetic nerve terminals, modulating cardiovascular function. The net hypothalamic effect -- reduced NPY/AgRP activity and maintained POMC activity -- shifts the energy balance toward satiety.
Ileal Brake Mechanism
Nutrient detection by L cells in the ileum and colon triggers PYY release proportional to caloric density and fat content. PYY slows gastric emptying and small intestinal transit by activating Y2 receptors on enteric neurons, ensuring that luminal nutrients are fully digested and absorbed before the next meal bolus arrives. This coordinating function explains why bariatric procedures that accelerate delivery of nutrients to the ileum (gastric bypass, sleeve gastrectomy) produce dramatically elevated postprandial PYY.
Research Summary
Appetite Reduction in Humans
Phase 2IV PYY3-36 infusion in lean humans reduces appetite by 30% and caloric intake at subsequent meals. Obese subjects show attenuated but still significant responses. Multiple Phase 2 trials of SC PYY3-36 and longer-acting PYY analogs (semaglutide co-development context) have been conducted. Results support meaningful appetite reduction, though GI side effects (nausea, diarrhea) limit dose escalation.
Bariatric Surgery Mechanism
Well EstablishedRoux-en-Y gastric bypass produces 10-fold increases in postprandial PYY, more than sleeve gastrectomy (2-3 fold) and vastly more than gastric banding. The magnitude of PYY response correlates with satiety improvement and long-term weight loss maintenance. Combined elevations in GLP-1 and PYY after bypass are proposed as key neuroendocrine mediators of sustained weight loss beyond restriction.
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Research Protocols
| Goal | Dose | Frequency | Route |
|---|---|---|---|
| Appetite/satiety research | 0.8-1.3 pmol/kg/min IV infusion for 90 minutes before meal test | Per research session | Intravenous infusion |
No approved therapeutic form. Short half-life and GI side effects have challenged analog development. Combination with GLP-1 agonists may have additive benefit with reduced PYY dose required.
Interactions
Safety Profile
IV PYY infusion produces dose-dependent nausea, limiting achievable doses in research settings. SC injection of longer-acting analogs shows improved GI tolerability. No cardiovascular, hepatic, or renal safety signals identified. Reduction in GI motility may cause constipation with sustained use. Endogenous PYY deficiency in obesity supports physiological replacement rationale. No long-term human safety data for therapeutic analogs.
References
- [1]Batterham RL, et al. Gut hormone PYY3-36 physiologically inhibits food intake. Nature. 2002;418(6898):650-654.
- [2]Le Roux CW, et al. Gut hormone profiles following bariatric surgery favor an anorectic state, facilitate weight loss, and improve metabolic parameters. Ann Surg. 2006;243(1):108-114.