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

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 present study was that limiting food intake to the typically inactive period in addition to high-salt (HS) feeding will disrupt the diurnal rhythm of renal Na excretion. Male Sprague-Dawley rats were placed on either normal-salt (NS; 0.49% NaCl) or HS (4% NaCl) diets. Rats were housed in metabolic cages and allowed food ad libitum and then subjected 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 with 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 HS intake combined with iTRF impairs circadian mechanisms associated with renal Na excretion. Timing of food intake normally has little effect on the diurnal pattern of Na and water excretion. However, rats on a high-salt diet were unable to maintain this pattern, yet K excretion was more readily adjusted to match timing of intake. These data support the hypothesis that Na and water homeostasis are impacted by timing of high-salt diets.