Short-term daytime restricted feeding in rats with high salt impairs diurnal variation of Na⁺excretion

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Night shift work increases risk of cardiovascular disease associated with an irregular eating schedule. Elevating this risk is the high level of salt intake observed in the typical Western diet. Renal Na+ excretion has a distinct diurnal pattern, independent of time of intake, yet the interactions between the time of intake and the amount of salt ingested are not clear. The hypothesis of the current study is that limiting food intake to the typically inactive period in addition to high salt feeding will disrupt the diurnal rhythm of renal Na+ excretion. Male Sprague Dawley rats were placed on either normal (NS, 0.49% NaCl) or high (HS, 4% NaCl) salt diets. Rats were housed in metabolic cages and allowed food ad libitum and then subject to inactive period time-restricted feeding (iTRF) for 5 days. As expected, rats fed NS and allowed food ad libitum had a diurnal pattern of Na+ excretion. The diurnal pattern of Na+ excretion was not significantly different after 5 days of iTRF compared to ad libitum rats. In response to HS, the diurnal pattern of Na+ excretion was similar to NS fed rats. However, this pattern was attenuated after 5 days of HS iTRF. The diurnal excretion pattern of urinary aldosterone was abolished in both NS iTRF and HS iTRF rats. These data support the hypothesis that high salt intake combined with iTRF impairs circadian mechanisms associated with renal Na+ excretion.