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

Abstract

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.

Mid-Point of the Active Phase Is Better to Achieve the Natriuretic Effect of Acute Salt Load in Mice

“…Gizowsk and Bourque reported that the injection of hypertonic saline significantly phase-advanced the circadian locomotor activity of mice [ 34 ]. Furthermore, HSD consisting of 4.0% NaCl restricted to inactive phase eating impaired the urinary Na + excretion rhythm whereas, normal diet did not [ 35 ]. Our HSD results, which included 1.6% NaCl, showed a more distinct difference in times of Na + and K + excretion than the normal diet; however, other studies, such as Oike et al [ 33 ], used NaCl concentrations up to 4.0% NaCl, so the results may have changed with a phase advance.…”

“…Zhang et al reported that feeding restricted to the inactive phase led to reversed BP rhythm in mice [ 40 ]. Rhoads et al reported that five days of time-restricted feeding led to a loss of plasma aldosterone rhythm in rats [ 35 ]. In both reports, administration of inactive time-restricted feeding consisting of a normal diet did not change the urinary Na + excretion rhythm.…”