Is there circadian variation of plasma endothelin (ET-1) in patients with systemic scleroderma (SSc)?

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Forty-three patients with systemic scleroderma (SSc), 10 with non-SSc (6 cases of systemic lupus erythematosus and 4 cases of dermatomyositis), 14 cases of mild- or non-sclerotic type of scleroderma with capillaroscopic abnormalities of nailfolds (SSD; scleroderma spectrum disorders) and 10 healthy volunteers (HC) were subjected to examination of plasma levels of endothelin-1 (ET-1). The sex ratios (male/female) in the patients with SSc, non-SSc and HC were 7:36, 4:6 and 0:10, and the ranges of their ages were 22–74, 19–78 and 33–62 years old, respectively. The plasma levels of ET-1 in SSD, SSc (Barnett I;15), SSc (Barnett II;16), SSc (Barnett III;12 cases), non-SSc and HC were 1.67±0.37, 2.04±0.58, 2.04±0.68, 1.85±0.41, 1.91±0.7 and 1.31±0.34 pg/ml, respectively, confirming previous results from other laboratories. The plasma levels of ET-1 statistically differ between each collagen disease (SSD, SSc and non-SSc) and HC using Student's t-test ( P<0.05). Although a statistically significant difference was obtained in the plasma levels of ET-1 between the SSc group (6 cases) and HC (6 cases) measured at 06:00, 12:00, 18:00 and 24:00 h, there was no significant circadian variation of plasma levels of ET-1 at these times in both the SSc group and HC. The present study revealed that (1) the ET-1 level in HC showed no circadian fluctuation, and remained at a low level (0.8–1.6 pg/ml). (2) When compared to HC, ET-1 in blood plasma of patients with SSc was elevated (0.3–3 pg/ml) throughout the day and night ( P<0.05). (3) ET-1 tended to increase more at midnight (24:00 h) in the SSc group without PSL treatment, though no statistical significance was obtained. (4) TAT showed a significant increase at noon (12:00 h) suggesting coagulation activity in patients with SSc, but PIC did not show a significant increase compared to HC. In conclusion, the observed increase of vasoconstrictive ET-1 in the patients with SSc throughout the day and night may make maintenance of peripheral blood flow more difficult, may have some biological origin and should be further investigated.