Bile Acid Signaling as an Upstream Modulator of RAAS and Chloride Homeostasis, V 1.1, February 2026

Electrolyte stability emerges from coordinated interaction between upstream metabolic signaling, renal execution mechanisms, and systemic hydration state. Hyperchloremia is commonly interpreted as a primary electrolyte disturbance; however, physiologic evidence indicates that chloride elevation frequently reflects downstream concentration effects associated with dehydration and renal conservation responses rather than primary dysregulation of chloride transport itself. Bile acids function as endocrine signaling molecules through receptors including the farnesoid X receptor (FXR) and TGR5, influencing vascular tone, autonomic regulation, inflammatory signaling, and metabolic state. These pathways intersect with regulatory systems governing renal blood flow, nitric oxide availability, and renin–angiotensin–aldosterone system (RAAS) activity. Renal nitric oxide signaling represents a critical execution interface translating upstream regulatory state into renal transport behavior. Nitric oxide modulates afferent arteriole tone, renin release, and tubular electrolyte handling, thereby influencing renal conservation responses during dehydration. Altered nitric oxide availability may promote a renal conservation state characterized by relative chloride retention and reduced bicarbonate concentration without requiring structural kidney damage. Within this framework, bile acid signaling is proposed to influence renal dehydration response indirectly through upstream endocrine, autonomic, and vascular regulatory pathways. Hyperchloremia emerges as a downstream concentration marker reflecting dehydration and renal conservation state rather than a primary regulated variable. This mechanistic continuity model provides a physiologic bridge linking bile acid signaling, renal nitric oxide execution, dehydration, and electrolyte stability. It integrates established FXR and nitric oxide physiology with clinical patterns of hyperchloremia observed in the absence of intrinsic renal failure. This work is hypothesis-generating and intended to support conceptual integration and future investigation rather than establish clinical efficacy. This work is part of the Lantern of Sulfur (LoS) framework, a systems-level model of electrolyte balance, RAAS signaling, and physiological coordination. For the complete Lantern of Sulfur framework, reading order, and updated convergence dynamics materials, see the Lantern of Sulfur Master Index (Concept DOI): https://doi.org/10.5281/zenodo.17915492