Original Article

Kappa-opiate receptor in blood vessels

Feng-yan Sun, Gui-hua Yu, An-zhong Zhang


[3H]etorphine was used in Scatchard analysis and displacement studies on membrane preparations from both rat brain and rabbit mesentery and aorta (adventitia stripped off). Scatchard plots revealed an affinity constant, KD. for rat brain of 0.30 nM and a maximum binding. Bmax of 12 fmol/mg tissue. Rabbit blood vessel had a higher KD of 0.61 nM and a much lower Bmax of 0.17 fmol/mg tissue. The subtypes of opiate receptors were analysed with Tyr-Pro-NMePhe-D-Pro-NHz (a specific mu agonist). D-Ala2-D-Leu6-enkcphalin (delta agonist). Dynorphinl-13 (kappa agonist). and Met6-enkephalin-Arge-Pher (an opioid peptide distributes in some peripheral tissues with concentrations much higher than that in the brain). Their IC60 for displacing [3H]etorphine binding in the brain were 820, 82, 12, and 34 nM respectively. But in the blood vessel, only dynorphin could displace [3H] etorphine binding with an IC60 of 20+5.5 nM (SD) while the other 3 opioid peptides showed very weak inhibition (IC60>1000 nM). These results suggest an existence of opiate receptor in blood vessels which is different from that in the brain. and is mainly kappa in nature.

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