[The circadian cycle of endothelin-1 in healthy persons]

The possible circadian rhythmicity of endothelin-1 was investigated. Radioimmunoassay method was used in 5 clinically healthy male subjects aged 24-32 years. Blood samples were collected at 4-hour intervals over a period of 24 hours. Data for ET-1 were fitted to a 24-hour cosine curve. Statistically significant curves were found in two subjects (maximum at 4 p.m. and minimum at 10 p.m.), one did not yield a statistically significant curve and in two subjects despite the fact that the curves were not presented. Nevertheless, the circadian rhythmicity in our study was not confirmed according to our results it could not be excluded. (Fig. 2, Tab. 2, Ref. 23.)