The effect of instability stress and exogenous oxytocin on the number of the natural killer cells in peripheral blood and spleen in male rats

  Social stresses which affect the immune system and the physiological features of the organs, cause a range of disorders, as well as psychopathological deficits such as depression and anxiety. The oxytocin hormone which is produced in the central nervous system and some tissues plays an important role in reducing anxiety and depression caused by stress. Also, social stress affects the natural killer lymphocytes of the innate immune system that play an important role in defense against tumor and viral infections. The purpose of this study was to investigate the effect of unstable stress and extracellular oxytocin on the number of natural killer cells in rats exposed to this stress.

Wistar rats were subjected to instability stress for 21 days, hence their cage-mate were changed every three days. From the 11th day, a group of rats received 20 microliter and the other group received 40 microliter of 1 mg/ml oxytocin and the control group received normal saline by intranasal rout and there was a healthy control group without any injections. At the end of study, the animals were anesthetized and then were killed. Blood sample and spleen tissue were obtained and the number of NK cells was counted by flow cytometry with CD3-CD161+ markers.

The number of NK cells in peripheral blood in the instability stress groups treated with 20 and 40 μL doses of oxytocin (3.6 ± 1.8, 4.4 ± 0.9) compared with healthy controls (4.5 ± 2.1) did not have a significant difference. In the spleen, the number of NK cells in the instability stress group treated with doses of 20 and 40 μL was (4.4 ± 1.6, 4.7 ± 1.1), which was significantly higher than the control group (2.2 ± 0.6) (P value = 0.025 and P value = 0/008, respectively).

Instability stress combined with treatment with 20 and 40 μL of oxytocin increases the number of NK lymphocytes in the spleen of the rats, which in fact indicates that this synergistic effect puts the immune system in a precautionary state to confront infections and cancer