Detection and distribution of opioid peptide receptors in porcine myocardial tissue

There is growing evidence that opioid peptide receptors (OPRs) play an important role in cardiovascular function. Many studies have been conducted in swine, in view of their anatomic and physiologic similarities to humans. Until now, the presence and particularly distribution of OPRs has been unclear. Porcine myocardial tissue was obtained from both the left and right atria and ventricles. Expression of mRNA for mu-, delta- and kappa-OPR was determined by reverse transcription PCR. OPR proteins were detected by Western blot, distribution and cellular location were identified using immunohistochemistry. Homogenous expression of mRNA and protein for delta- and kappa-OPRs were demonstrated in all porcine myocardial tissue tested, whereas expression of mu-OPR mRNA was not demonstrated in any of the tissues tested. This study demonstrates the expression of delta- and kappa-OPRs in porcine myocardial tissue. No differences in distribution of delta- and kappa-OPRs were found between the four heart cavities. Modulation of cardiac function by delta- and kappa-OPR agonists or antagonists is therefore possible, while mu-OPR-mediated direct cardiac effects appear unlikely, due to nonexpression of the receptor. This study demonstrates that porcine studies can further elucidate the role of OPRs in cardiac (patho-)physiology. (C) 2014 Elsevier Ltd. All rights reserved.