[Alpha interferon interaction with opiate receptors in the rat brain].

The preferential interactions of alpha-interferon (alpha-IFN) with delta and mu opiate receptors were studied. alpha-IFN (specific antiviral activity 2 X 10(3) U/mg protein) was shown to inhibit in the competitive manner 3H-naloxone and 3H-D-ala2, D-leu5-enkephalin (3H-DADL) specific binding to opiate receptor subpopulations. alpha-IFN was much more effective in decreasing 3H-DADL than 3H-naloxone binding in opiate receptors: K1 values averaged 160 +/- 30 and 1150 +/- 80 U/ml, respectively. IFN effective concentrations inhibiting 50% of 3H-naloxone opiate receptor binding in the absence or presence of 100 mmol/l NaCl were similar, and the "sodium shift" value was equal to 1. The independence of alpha-IFN activity of the presence of NA+ cations suggests the antagonist character of alpha-IFN interaction with opiate receptors. Thus, alpha-IFN employed appears to be an alpha-selective ligand displaying the in vitro properties of "pure" morphine antagonists.