<i>In Vivo</i> Measurement of Intestinal Permeability to Macromolecules in Adult Zebrafish ( <i>Danio rerio</i> )

Intestinal permeability plays a crucial role in intestinal barrier function. Altered intestinal permeability is well documented in numerous chronic diseases and may serve as a risk factor for disease onset as well as a target for innovative therapeutic strategies. While reliable and sensitive approaches for studying intestinal permeability have been established in animal models, such as mice and zebrafish larvae, methods for investigating this in adult zebrafish remain a considerable challenge. The zebrafish has emerged as a valuable model for studying intestinal development, physiology, and disease. Moreover, zebrafish offer certain advantages over rodent models, such as the ability to evaluate the dynamic interactions of labeled markers <i>in vivo</i> and in real time. In this study, we present a comprehensive pipeline for assessing <i>in vivo</i> intestinal permeability in adult zebrafish using fluorescent-labeled dextran. Detailed protocols for fish handling, reagent preparation, optimization of reagent dosage and delivery routes, and quantification of fluorescent markers in extraintestinal sites are provided. Our findings suggest that zebrafish hold promise as an alternative model for <i>in vivo</i> investigations of intestinal permeability induced by genetic, pathophysiological, and/or pharmacological events.