OBJECTIVETo investigate the relationship of the circadian rhythm of the urine volume and urine electrolytes excretion rate and the daily expression pattern of the clock genes and clock-controlled genes with the water electrolyte transportation circadian pattern in rat kidneys.

METHODSMale adult SD rats were exposed to in a light:dark (12:12) cycles. We collected two period urine from zeitgeber time (ZT)00:00-ZT12:00 (light time,rest period) and ZT12:00-24:00 (dark time,activity period) and then compared the urinary excretion rates of volume, sodium, potassium, and chloride at light time with those at dark time. Rats were sacrificed every 4 hours throughout a 24-hour day-night cycle. Circadian clock gene CLOCK, BMAL1,Per1,Per2,Cry1,Cry2 and kidney specific clock-controlled gene NHE3,αENaC、NCC,Ptges,V1aR,V2R expression were profiled by real-time quantitative polymerase chain reaction. Data were analysed by a partial Fourier analysis and a stepwise regression technique.

RESULTSUrine volume and urine potassium excretion rate displayed high level at dark time and low at light time in SD rats (P<0.05),and urine sodium and chloride excretion rate also showed the trend(P>0.05).Clock gene CLOCK,BMAL1,Per1,Per2,Cry1,Cry2(P<0.05)and kidney specific clock-controlled gene NHE3, αENaC, NCC, Ptges, V1aR, V2R (P<0.05)mRNA expression showed circadian pattern,and the peak times of the genes were in the dark time.

CONCLUSIONUrine volume and urine electrolyte excretion rate which displayed circadian pattern were temporally coupled with the rhythm of expression of clock and clock-controlled genes associated with water electrolyte transportation in rats kidney.