DAILY CYCLE OF BHLH-PAS PROTEINS, AH RECEPTOR AND ARNT, IN MULTIPLE TISSUES OF FEMALE SPRAGUE-DAWLEY RATS

The aryl hydrocarbon receptor (AhR) shares a common PAS domain with a number of genes that exhibit a pronounced circadian rhythm, Therefore, this study examined the daily cycle of AhR and AhR nuclear translocat or (Arnt) protein expression in multiple tissues of female Sprague-Daw ley rats. Rats were euthanized at 4, 7, and 11 AM and 4, 7, and 11 PM after which whole tissue homogenates were made from multiple tissues. Western blot analysis showed that the daily cycle of relative AhR prot ein expression exhibits a similar oscillation pattern in the liver, lu ngs, and thymus. The daily cycle of relative Arnt protein expression e xhibits a similar oscillation pattern in the liver and lungs. The appa rent daily cycle of AhR and Amt protein expression in multiple tissues was not observed within the spleen. This preliminary report is the fi rst study to suggest that the PAS proteins, AhR and Amt, exhibit a dai ly oscillation pattern within multiple target tissues which may give i nsight into the tissue-specific toxic and biochemical responses mediat ed through this dimerization pair, as well as the physiological functi on of these proteins. (C) 1998 Academic Press.