Characterization of [3H]Mazindol Binding in Rat Brain: Sodium‐Sensitive Binding Correlates with the Anorectic Potencies of Phenylethylamines

Abstract

Saturable low-affinity binding sites for [³H]mazin-dol have been demonstrated in crude synaptosomal membranes from rat brain using both a centrifugation and a fil-tion assay. Studies on the regional distribution of these binding sites revealed that the hypothalamus and brainstem had the highest density of sites. Kinetic analysis of the binding of [³H]mazindol to hypothalamic membranes demonstrated a single class of noninteracting binding sites with an apparent affinity constant (K_D) of 10.2 ± 0.7 μM and maximal number of binding sites (B_max) of 786 ± 94 pmol/mg of protein. Specific [³H]mazindol binding was rapidly reversible, temperature sensitive, labile to pretreatment with proteolytic enzymes, and inhibited by physiological concentrations of sodium. In most peripheral tissues, such as the liver and kidney, very low levels of binding were observed; however, the adrenal gland had a relatively high density of sites. The potency of a series of anorectic drugs in inhibiting specific [³H]mazindol binding to hypothalamic membranes was highly correlated with their anorectic potencies in rats, but not with their motor stimulatory effects. These results suggest the presence of a specific drug recognition site in the hypothalamus that may mediate the anorectic activity of mazindol and related phenylethylamines.