Minimal daily variations of plasma and urinary endothelin-1 in healthy subjects

The daily profiles of both the plasma level and the urinary excretion rate of endothelin-1 were examined in 13 healthy volunteers (9 males and 4 females, aged 22 +/- 1 [SEM]). Plasma endothelin-1 (PET) was measured after a one-hour recumbency every 6 hours at 8 a.m., 2 p.m., 8 p.m. and 2 a.m. and the urinary excretion rate of endothelin-1 (UET) was determined in the urine collected every 6 hours. PET was found to be quite stable throughout the day, being 1.57 +/- 0.25 pg/ml at 8 a.m., 1.88 +/- 0.21 at 2 p.m., 2.2 +/- 0.24 at 8 p.m. and 1.90 +/- 0.20 at 2 a.m. After a one-hour ambulation, PET showed no statistical difference. UET also remained unchanged for each 6-hour collecting period, measuring 4.61 +/- 0.69, 3.98 +/- 0.46, 4.63 +/- 0.73 and 3.42 +/- 0.49 ng/hr, respectively. The absence of any daily variations in either PET or UET thus suggests that apparently no specific considerations need be applied regarding the time of taking samples to measure the plasma and urinary endothelin-1.