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1 Physiology & Pharmacology, University of Western Ontario, London, ON, Canada
* To whom correspondence should be addressed. E-mail: Morris.Karmazyn{at}fmd.uwo.ca.
Leptin, the 16kDa peptide hormone product of the ob gene, is produced primarily by adipocytes and was initially thought to exert its effects exclusively through actions on the hypothalamus via distinct leptin receptors termed OB-R. However, recent data shows that leptin is produced elsewhere and that receptors are present in many other tissues. Using real time PCR, we determined whether leptin and its receptors are present in the rat heart, and demonstrated regional distribution patterns, gender differences as well as the effect of ischemia and reperfusion. Gene expression of leptin and its receptors (OB-Ra, OB-Rb and OB-Re) was identified in both myocytes and whole heart homogenates from all regions of the heart of both male and female rats with highest abundance in the left atria and right atria of male and female rats, respectively. No differences in regional distribution of OB-R were evident in male rat hearts. In females, expression was highest in the right atria for all 3 isoforms and was significantly greater than in males. Ischemia and reperfusion significantly down regulated leptin and OB-R expression although this was more pronounced in male rat hearts. Leptin release in the coronary effluent was also detected using ELISA although this was generally unaffected by global ischemia and reperfusion. Our results demonstrate for the first time the presence of the leptin system, including the peptide and its receptors, in all regions of the rat heart. In view of emerging evidence for cardiac effects of leptin it is proposed that the heart is a target for leptin action and that the peptide modulates function through a paracrine- or autocrine-dependent manner.
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