Effect of angiotensin II on rhythmic per2 expression in the suprachiasmatic nucleus and heart and daily rhythm of activity in Wistar rats

Abstract

Endogenous daily rhythms are generated by the hierarchically organized circadian system predominantly synchronized by the external light (L): dark (D) cycle. During recent years several humoral signals have been found to influence the generation and manifestation of daily rhythm. Since most studies have been performed under in vitro conditions, the mechanisms employed under in vivo conditions need to be investigated. Our study focused on angiotensin II (angII)-mediated regulation of Per2 expression in the suprachiasmatic nuclei (SCN) and heart and spontaneous locomotor activity in Wistar rats under synchronized conditions. Angiotensin II was infused (100 ng/kg/min) via subcutaneously implanted osmotic minipumps for 7 or 28 days. Samples were taken in 4-h intervals during a 24 h cycle and after a light pulse applied in the first and second part of the dark phase. Gene expression was measured using real time PCR. Locomotor activity was monitored using an infrared camera with a remote control installed in the animal facility. Seven days of angII infusion caused an increase in blood pressure and heart/body weight index and 28 days of angII infusion also increased water intake in comparison with controls. We observed a distinct daily rhythm in Per2 expression in the SCN and heart of control rats and infused rats. Seven days of angII infusion did not influence Per2 expression in the heart. 28 days of angII treatment caused significant phase advance and a decrease in nighttime expression of Per2 and influenced expression of clock controlled genes Rev-erb alpha and Dbp in the heart compared to the control. Four weeks of angII infusion decreased the responsiveness of Per2 expression in the SCN to a light pulse at the end of the dark phase of the 24 h cycle. Expression of mRNA coding angiotensin-converting enzyme (ACE) and angiotensin-converting enzyme 2 (ACE2) showed a daily rhythm in the heart of control rats. Four weeks of angII infusion caused a decrease in amplitude of rhythmic expression of Ace, the disappearance of rhythm and an increase in Ace2 expression. The Ace/Ace2 ratio showed a rhythmic pattern in the heart of control rats with peak levels during the dark phase. Angiotensin II infusion decreased the mean Ace/Ace2 mRNA ratio in the heart. We observed a significant daily rhythm in expression of brain natriuretic peptide (BNP) in the heart of control rats. In hypertensive rats mean value of Bnp expression increased. Locomotor activity showed a distinct daily rhythm in both groups. Angiotensin II time dependently decreased ratio of locomotor activity in active versus passive phase of 24 h cycle. To conclude, 28 days of subcutaneous infusion of angII modulates the functioning of the central and peripheral circadian system measured at the level of Per2 expression and locomotor activity.