Thermoregulatory, physiological, and intestinal responses to functional waters in heat-stressed rats.

Background and aim: Climate change and global warming have intensified the challenges of heat stress (HS) in mammals, compromising thermoregulation, hydration, and physiological stability. Functional waters such as alkaline reduced water (ALKA), Zamzam water (ZMZM), and ozonated water (OZON) have been proposed to provide therapeutic and protective benefits. However, limited research has explored their roles in thermoregulation under chronic HS. This study investigated the effects of ALKA, ZMZM, and OZON on thermophysiology, serum metabolites, and intestinal morphology in Wistar rats exposed to variable thermal climates.

Materials and methods: Seventy male Wistar rats (8 weeks old, 180-200 g) were randomized into five groups (n = 14): Control, distilled water (DIST), ALKA, ZMZM, and OZON. The experiment lasted 71 days, consisting of thermoneutral zone (TNZ; days 0-7), HS (32.3 ± 0.8°C; days 8-35), and a return to TNZ (days 36-71). Core body temperature (Tcore) was monitored using thermal microchips and loggers. Daily water intake, body weight, serum biochemical markers, and intestinal villi morphology were evaluated. Data were analyzed using repeated measures analysis of variance and general linear model procedures.

Results: HS induced hyperthermia and increased daily water intake by 69.2% across all groups. ZMZM significantly reduced Tcore, especially at night, and increased water intake during HS. OZON consumption elevated water intake during TNZ, reduced serum creatinine, and enhanced alkaline phosphatase levels, while both OZON and DIST groups exhibited elevated antidiuretic hormone levels. ALKA intake significantly reduced serum sodium+ and chloride- levels under post-HS TNZ. Histological analysis revealed that ZMZM markedly increased villus length, width, and crypt depth in the duodenum, jejunum, and ileum, indicating enhanced intestinal absorptive capacity.

Conclusion: ZMZM demonstrated superior thermoregulatory and intestinal benefits, supporting hydration, physiological recovery, and intestinal health during and after HS. OZON showed nephroprotective and metabolic modulation potential, while alkaline water contributed to electrolyte regulation. These findings highlight the potential of functional waters as supportive strategies against HS, warranting further translational studies in livestock and humans.