Timing of food intake differentially impacts urinary electrolyte and aldosterone excretion
Authors: Johnston Jermaine G. , Speed Joshua S. , Jin Chunhua , Zhang Dingguo , Pollock David M. 
Published: June 2021

The time‐of‐day variation in sodium excretion can be regulated by many different peptides and hormones, such as aldosterone. Numerous studies have shown that the circadian clock modulates the ability of aldosterone to regulate sodium balance, indicating a functional consequence of their interaction. Normally, renal sodium excretion has a distinct diurnal pattern, independent of time of intake, yet the interaction between the time of intake and the amount of salt ingested has yet to be determined. Our lab sought to determine what effect the timing of food intake has on the diurnal rhythm of renal electrolyte excretion, and whether or not this timing affects aldosterone as well. Male Sprague Dawley rats were implanted with telemetry devices to monitor mean arterial pressure (MAP). Following at least 7 days of recovery, rats were housed in metabolic cages and placed on a normal salt diet (0.49% NaCl). Following two days of baseline urine collections at 12‐hour intervals (Zeitgeber Time [ZT] 0 to ZT12 [lights on] or ZT12‐ZT24 [lights off]) under ad libitum feeding conditions, we restricted their access to food for 7 days to only their inactive period (ZT0‐ZT12). Rats were given free access to water during the reverse feeding (RF) conditions. As expected, rats allowed food ad libitum had a diurnal rhythm in sodium excretion as evidenced by a significantly higher sodium excretion during their active period (P<0.05); active:inactive (A/I) sodium excretion was (2.82 ± 0.20). The rhythm in sodium excretion was not significantly different after 7 days of RF compared to ad libitum rats (2.03 ± 0.28 A/I, P=NS vs. ad libitum). As expected, potassium excretion was significantly greater during the active period in rats fed under ad libitum conditions (P<0.05; A/I = 2.32 ± 0.16). Interestingly, RF significantly reduced the diurnal variation in urinary potassium excretion (0.89 ± 0.16, P<.05 vs. ad libitum) as potassium excretion remained high during the inactive period. Although urinary aldosterone levels were similar in both ad libitum and RF conditions during the active period (89 ± 17 vs. 97 ± 18 pg/12 hr, P=NS), RF prevented the normal diurnal rhythm in aldosterone excretion resulting in significantly higher levels during the inactive period compared to ad libitum (138 ± 25 pg/12 hr vs. 25 ± 8, respectively, P<0.05). There were no differences in 12‐hour MAP or activity between ad libitum and reverse feeding conditions. Our findings suggest that consuming food during the inactive phase impairs the diurnal variation in aldosterone production. In addition, the inappropriately high aldosterone excretion during the inactive period appears to be consistent with elevated potassium excretion during this period as well.Support or Funding InformationThis research was supported in part by the NHLBI Program Project grant HL136267, the NIH Career Development Award K99 HL127178, the NIGMS Pre‐doctoral Training Grant in Cell and Molecular Biology (CMB) T‐32 Training Grant T32GM008111‐30, and the UAB School of Medicine AMC21 Multi‐Investigator Grant.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.