Circadian rhythm neuropeptide levels among bipolar disorder patients

Objective: According to the previous studies, it has been noted many times that circadian rhythm is disrupted in bipolar disorder. This suggests that BPD may also have circadian rhythm disorders in the etiology. We aimed to investigate somatostatin (SST), neuropeptide-Y (NPY), arginine vasopressin (AVP), vasoactive intestinal peptide (VIP) and cortisol levels, which are known as neuropeptide markers related to circadian rhythm in patients with bipolar disorder euthymic period. Method: Thirty nine patients diagnosed as bipolar disorder euthymic episode according to DSM-5 and 38 healthy controls enrolled into the study. Serum somatostatin (SST), neuropeptide-Y (NPY), arginine vasopressin (AVP), vasoactive intestinal peptide (VIP) and cortisol measurements were done in biochemistry laboratory of Gaziantep University. Results: When SST, NPY, VIP, AVP and cortisol levels were compared between bipolar disorder euthymic episode patients and control group; SST, NPY, VIP and cortisol levels were significantly lower in the patient group than the control group (p=0.001, p =0.001, p=0.001, p=0.001). According to the correlation analysis, SST levels were found to have a high linear correlation in the positive direction with VIP and AVP (r=0.777, p=0.001 for VIP; and r=0.574, p=0.001 for AVP). Conclusion: SST, NPY, VIP, AVP and cortisol levels were lower in bipolar disorder euthymic episode patients when compared with controls in concordance with many of the previously conducted studies. In the earlier studies, data have been obtained about the effects of neuropeptide markers related to circadian rhythm on behavior, sleep, anxiety and relevant hypotheses have been established. In the light of these studies in the literature, our study suggests that bipolar disorder may be associated with a decrease in circadian rhythm-related neuropeptide levels in one of the causes of behavioral and sleep disturbances seen in the clinical features of patients with bipolar disorder euthymic episode. Our study is the first one to examine SST, NPY, VIP, AVP and cortisol levels in euthymic episode of bipolar disorder together, therefore it may significantly contribute to the literature.