TISSUE DISTRIBUTION OF OPIOID RECEPTOR GENE-EXPRESSION IN THE RAT

The endogenous opioid peptides have multiple physiological actions at both a central and peripheral level which are mediated by 3 main class es of opioid receptors, mu, delta and kappa. The rat mu, delta and kap pa opioid receptors have recently been cloned and their distribution o f expression in the central nervous system has been mapped. In these s tudies we have used the reverse transcriptase polymerase chain reactio n and Southern blotting to determine the distribution of expression of the mu, delta and kappa opioid receptors in the peripheral tissues of the rat. All 3 opioid receptors were found to be widely expressed in several peripheral tissues including the small intestine, large intest ine, adrenal, kidney, lung, spleen, testis, ovary and uterus. In the s tomach, delta and kappa but not mu opioid receptor transcripts were de tected. Predominantly delta transcripts were detected in the heart, wi th no mu and only a weak signal for the kappa receptor. In the liver m u and delta but not kappa transcripts were present. Opioid receptor ex pression was not detected in endothelium or synovium. There is therefo re a broad, but tissue specific distribution of opioid receptor expres sion in the periphery of the rat, suggesting that the endogenous opioi d peptides play an endocrine, paracrine, or autocrine role in the regu lation of physiology at a peripheral as well as central level. (C) 199 6 Academic Press. Inc.