Comparative study of the role of nitric oxide in the regulation of food intake across vertebrates

IMPORTANCE: Nitric oxide (NO), synthesized from L-arginine by nitric oxide synthases (NOS), acts as a conserved signaling molecule involved in the regulation of food intake across animal taxa. Understanding its function has gained importance in veterinary medicine, animal production, and comparative physiology, especially given species-specific differences in arginine metabolism and immune-nutritional interactions. OBSERVATIONS: This review provides a comparative synthesis of the role of NO in appetite regulation in mammals, birds, and aquatic animals, highlighting conserved mechanisms, species-specific differences, and gaps requiring further investigation. In mammals, NO modulates hypothalamic circuits controlling satiety and hunger in a bidirectional, energy-dependent manner. Birds, lacking endogenous arginine synthesis, show reduced feed intake with elevated NO levels. In fish, NO-especially via agmatine-suppresses feeding by downregulating orexigenic signals and enhancing insulin-mediated pathways. CONCLUSIONS AND RELEVANCE: NO functions as a conserved but flexible regulator of food intake across taxa. Future studies employing molecular, nutritional, and behavioral tools are needed to clarify species-specific mechanisms and optimize NO-targeted feeding strategies in production animals.