Differential circadian expression of endothelin-1 mRNA in the rat suprachiasmatic nucleus and peripheral tissues

The vasoconstrictor endothelin-1 (ET-1) is implicated in normal neuronal functions. Here we show the circadian expression of ET-1 mRNA in the rat suprachiasmatic nucleus (SCN) that is considered to be the location of the central circadian pacemaker, as well as in peripheral tissues including the brain, heart, and lungs. The expression of ET-1 in the SCN oscillated with a peak at Zeitgeber time (ZT) 4 under light-dark conditions. A significant number of cells in the SCN was stained with ET-1 probe during circadian time (CT) 6, but there was no significant staining at CT18 by mRNA in situ hybridization. The circadian rhythm of ET-1 mRNA in the whole brain also oscillated, but peaked at ZT20. Endothelin-1 expression in the lungs and heart peaked at ZT12 and ZT20, respectively. The results are the first description of the circadian expression of ET-1 mRNA. The diversity of rhythmic expressions among the SCN, whole brain, lungs and heart suggests that ET-1 has different functions in these tissues.