Autoradiographic localization of [3H]-pinoline binding sites in mouse tissues

Pinoline (6-methoxy-1,2,3,4-tetrahydro-beta-carboline) has been found in similar concentrations to those of melatonin in various mammalian tissues. The present study investigates the subcellular distribution of in vivo administered [3H]-pinoline in mouse tissues using light and electron microscopic autoradiography. The antioxidative capacity of pinoline was determined in vitro and compared with that of the structurally similar pineal hormone melatonin. Autoradiograms revealed that [3H]-pinoline was present in all tissues studied 30 min after administration, but in most tissues binding was nonspecific. Adrenal glands showed the highest specific binding for [3H]-pinoline 0.5-1 h after administration of the labelled compound. In all tissues a large amount (approximately 40%) of radioactivity was located in nuclei of cells. Specific nuclear binding was the highest in adrenal glands and cerebral cortex. Both pinoline and melatonin potently inhibited lipid peroxidation. Therefore, we suggest that pinoline may act in cells and nuclei as an antioxidant. Direct genomic effects of pinoline cannot be excluded.