Effects of acute stressors on the expression of oxytocin receptor mRNA in hearts of rats with different activity of HPA axis.

Objectives: Cardiovascular system is regulated by a diverse array of hormones, neurotransmitters and neuropeptides. Oxytocin and its receptors (OTR) were also shown to regulate cardiovascular functions and this hormone was even called cardiovascular hormone. In recent publication, we demonstrated the expression of mRNA of OTR by real-time quantitative PCR (RT qPCR) in all rat heart compartments. The aim of this study was to investigate the effects of acute restraint stress on OTR mRNA expression in two rat strains with different activity of HPA axis.

Methods: Adult male Sprague-Dawley and Lewis rats, the latter strain reported to have lower HPA activity, were used in RT qPCR studies and Wistar rats in immunofluorescent ones. Both acute restraint (IS) and this stress combined with the immersion of rats in water (ICS) lasted 60 min. Gene expression of OTR mRNA was estimated in all heart compartments after 1 or 3 hours after stress termination (IS1, IS3, ICS1, ICS3). The relative expression was calculated using 2(-ΔΔC)T method. In immunofluorescent studies we used commercial specific OTR antibodies.

Results: In RT qPCR studies we found higher expression of OTR mRNA in atria than in ventricles and no statistical differences between Sprague-Dawley and Lewis rats under basal conditions. Relative expression of OTR mRNA after 60 min lasting stress exposure differed in dependence on the stress type and partly on the time interval after the stress termination. When compared to controls, in rat left atria both stressors caused inhibition of OTR mRNA expression in both rat strains. In rat ventricles, which have very low OTR mRNA expression, there was a significant difference in the effect of two stressors. In most groups ICS displayed the increase of OTR mRNA expression if compared to IS groups. Immunofluorescent studies revealed changes induced by acute restraint stress in all heart compartments. The immunofluorescent studies suggested that acute stress induces higher colocalization of OTR with the nuclei than it was observed in the controls.

Conclusions: The expression of OTR mRNA in all heart compartments of controls as well as after stress exposure in Sprague-Dawley and Lewis rats support the notion that OTR plays a regulatory role in the cardiovascular system and is also involved in the regulations in the heart after stress. The immunofluorescent observation that OTRs coexpress in areas of cell nuclei in certain heart compartments and after acute stress, compared to controls, requires further studies.