Assessment the effect of NO inhibition on hippocampal normetanephrine level in stress and non-stress conditions in adult male rats

Nitric oxide (NO) has a role in the regulation of neurotransmitters release such as norepinephrine, in the hippocampus.Normetanephrine (NMN) is a metabolite of norepinephrine created by action of catechol-O-methyl transferase (COMT) on norepinephrine. Several studies have shown that various stresses increased release of norepinephrine and its metabolites. Therefore in the present study, the role of Nitric oxide in regulation of norepinephrine release and its metabolism was investigated by administration of L-NAME (NO synthase inhibitor) in stressed and non-stressed rats. For this purpose, 50 adult rats were divided into 10 groups, of which 5 groups were exposed to restraint stress while another 5 groups were without stress. These two set of groups included intact, saline and L-NAME (20, 40, 80 mg/kg). Thirty minutes after intraperituneal injection of L-NAME, brains removed, the hippocampus dissected, weighed, homogenized and centrifuged then amount of NMN measured by ELISA kit. The results showed that in non-stressed condition amount of NMN were significantly increased in group that received L-NAME (80 mg/kg) in comparison with other groups but in stress condition, amount of NMN was significantly decreased in groups that received L-NAME (20,40,80 mg/kg), in comparison with control and saline groups. Comparison between stress and non-stressed groups showed that stress alone cause an increase in amount of NMN in control and saline groups. In conclusion, NO synthesis inhibition produced opposite responses with respect to NMN amount in the presence or absence of stress, and probably L-NAME preventing the effect of stress on increasing NMN levels mediated by nitrergic pathway.