Although it has been reported that oxytocin stimulates lipolysis in adipocytes, changes in the expression of oxytocin receptor (OTR) mRNA in adipogenesis are still unknown. The present study aimed to investigate the expression of OTR mRNA during adipocyte differentiation and fat accumulation in adipocytes. OTR mRNA was highly expressed in adipocytes prepared from mouse adipose tissues compared to stromal-vascular cells. OTR mRNA expression was increased during the adipocyte differentiation of 3T3-L1 cells. OTR expression levels were higher in subcutaneous and epididymal adipose tissues of 14-week-old male mice compared to 7-week-old male mice. Levels of OTR mRNA expression were higher in adipose tissues at four different sites of mice fed a high-fat diet than in those of mice fed a normal diet. The OTR expression level was also increased by refeeding for 4 h after fasting for 16 h. Oxytocin significantly induced lipolysis in 3T3-L1 adipocytes. In conclusion, a new regulatory mechanism is demonstrated for oxytocin to control the differentiation and fat accumulation in adipocytes via activation of OTR as a part of the hypothalamic-pituitary-adipose axis.

Chemerin was identified as a novel adipokine highly expressed in adipose tissue, suggesting that it plays a role in the pathophysiology of obesity. Chemerin actions are primarily mediated through binding to receptor expressed in several tissues. Likewise, chemerin expression has been detected in a variety of extra adipose tissues, including liver and pituitary. However, the expression and regulation of chemerin and its receptor mRNA in the liver and pituitary as a link in the lipid metabolism were not cleared. Chemerin function at the liver and pituitary was assessed by analyzing the expressions of both chemerin and chemerin receptor gene. The levels of chemerin and chemerin receptor mRNA was not changed in the liver in mice fed high fat diet compared with normal diet. However, these genes were upregulated in the adipose tissue in mice fed high fat diet. Chemerin mRNA expression was down‐regulated in pituitary gland in mice fed high fat diet, however chemerin receptor was not changed. Chemerin gene expression was up‐regulated in pituitary during 12 h of fasting, while chemerin receptor was not affected. Insulin and glucose treatment for 6h in HepG2 cells increased chemerin gene expression. These results suggest that that chemerin, either locally produced from the liver and pituitary, may play an endocrine role in the control of lipid metabolism via its own receptor.