Systems Physiology of Dehydration-Renal Response Coupling in Pastoralist Communities of the Sahel Zone, North East Nigeria: A Longitudinal Analysis

Pastoralist communities in the Nigerian Sahel endure extreme environmental heat and episodic water scarcity, creating a unique natural laboratory for studying long-term physiological adaptation in renal water conservation mechanisms. This study applied a systems physiology approach to characterise the longitudinal dehydration-renal coupling response among Fulani pastoralists in Borno and Yobe States, North East Nigeria, advancing understanding of adaptive renal physiology in environmentally stressed human populations. A longitudinal cohort design enrolled 80 pastoralist adults assessed during the dry season peak dehydration phase and the wet season recovery phase over two years. Physiological measures included urinary osmolality, plasma osmolality, arginine vasopressin, renin-angiotensin-aldosterone system activity, urine aquaporin-2 excretion, and kidney function biomarkers. Systems modelling using differential equation-based compartmental analysis characterised the regulatory dynamics of fluid homeostasis across seasons. Mixed-effects models and phase-plane analysis were applied. Results demonstrated profound seasonal shifts in arginine vasopressin and aldosterone, with pastoralists mounting greater vasopressin responses per unit plasma osmolality elevation compared to urban controls, suggesting adaptive hypothalamic-neurohypophyseal sensitisation. Aquaporin-2 excretion tracked vasopressin with high fidelity. Renal function remained intact despite extreme dehydration cycles. The systems model successfully replicated observed physiological trajectories and identified arginine vasopressin sensitivity as the key regulatory parameter. This study provides original systems-level physiological evidence for adaptive renal-hormonal coupling in a climatically stressed Nigerian population, advancing fundamental physiology. Keywords: dehydration, renal adaptation, vasopressin, pastoralists, Sahel Nigeria.