Opiate binding in rat hearts: modulation of binding after hemorrhagic shock

[3H] Diprenorphine was used to measure binding in sectioned rat hearts. Saturable binding for concentrations up to about 20 nM was obtained in the right atrium and ventricle. Unlabeled diprenorphine displaced bound [3H] diprenorphine most effectively in the right atrium (up to 55%), as compared to less than 27% in the right ventricle and the remaining parts of the heart. Scatchard analysis of the binding in the right atrium revealed cooperative binding. The delta agonist [D-Ala2,D-Leu3] enkephalin, the kappa agonist ethylketocyclazocine, and levorphanol, but not the mu agonist [D-ala2,MePhe4,Gly-(ol)5] enkephalin or dextrophan competed variably with [3H]diprenorphine for the binding in the right atrium and ventricle. A significant decrease in binding was observed in the right atrium (-66%) and ventricle (-45%) of hearts removed from rats 2 h after hemorrhagic shock; 24 h after shock, recovery of binding was found. This novel observation suggests that the diprenorphine binding sites in the heart may be physiologically active receptors, involved in regulation of peripheral cardiovascular processes.