Aims: 

Circadian system consisting from central and peripheral oscillators employs several pathways to achieve optimal phase relationships between biological rhythms inside the body. TGR (mREN – 2)27 rats exerting normal rhythm of the heart rate and locomotor activity are characterized by gradual development of inverted blood pressure (BP) profile. Our study was aimed on possible involvement of melatonin and/or angiotensin II in this process.

Methods: 

TGR and control rats were synchronized to the light:dark cycle 12:12. Angiotensin II receptors AT1 mRNA expression was measured in the SCN, nucleus of the solitary tract (NTS) and area postrema. Melatonin was administered in a rhythmic manner and effect of its amplified rhythm on clock gene expression in the suprachiasmatic nucleus (SCN) and paraventricular nucleus (PVN) was investigated. Brain nuclei were isolated by punching technique and gene expression was measured by real time PCR.

Results: 

Melatonin administration caused increase in per2 expression in SCN at the end of the night in TGR as well as control rats. In PVN effect of melatonin on per2 expression was detectable only in control rats. Expression of AT1 mRNA was increased in the area postrema and NTS in TGR rats in comparison with control.

Conclusion: 

Effect of melatonin on clock gene expression seems to be tissue specific. This phenomenon may reflect melatonin receptor distribution. Increased expression of AT1 receptors in the brainstem indicates involvement of angiotensin II in generation of inverted BP in TGR rats that have up regulated rennin – angiotensin system.

Research was supported by grants APVV – 20 – 022704, VEGA 1/ 4328/ 07, VEGA 1/ 4343/ 07.