Circaoctohoran (about 8-hourly) chronome component of circulating human endothelin-1 in health

Endothelin-1 (ET-1) is a very potent vasoconstrictor. A study of 72 subjects sampled every 4 hours for 24 hours failed to reveal a circadian variation for ET-1, but an about-half-weekly component, assessed transversely, was found for ET-1. As a follow-up, plasma ET-1 was measured around the clock at 20-min intervals for 24 hours on a clinically healthy man, 27 years of age, while atriopeptin (AP) was determined on every fourth sample (at 80-min intervals). An about-8-hour component suspected but not assessable in the larger study is validated, whereas a circadian is demonstrated for atriopeptin. The different circaoctohoran versus circadian prominent frequencies of two related hormones suggest the operation of multiple mechanisms in circulatory coordination, rather than a master circadian oscillator.