Differential effects of sodium on two types of opiate binding sites.

Effects of Na⁺ on saturable naloxone binding were studied $\text{in vitro}$ using particulate fractions obtained from rat brain homogenates. Na⁺ stimulated the saturable naloxone binding in thalamus-hypothalamus regions, but inhibited it in cerebellum. These findings strongly support the hypothesis that two types of naloxone binding sites exist in brain tissues.