Stress increases endogenous benzodiazepine receptor ligand-monoamine oxidase inhibitory activity (tribulin) in rat tissues.

The presence of both MAO and benzodiazepine (BZ) receptor binding inhibitory activities in rat tissues has been reported previously. The two activities were similarly and unevenly distributed in the tissues. This dual inhibitory activity has been termed tribulin. We report here the effect of 1 1/2 hrs cold restraint stress on tribulin activity in rat tissues together with biochemical evidence to support the concept of a physiological role of tribulin. Stress induced a significant increment of both activities in heart and kidney while no significant changes were observed in the other tissues studied. Hearts and kidneys from stressed rats also showed a significant decrease of MAO activity, a significant increase of dopamine content and a significant decrease of the binding of 3H-Ro 5-4864 to peripheral BZ receptors. Scatchard analysis of the saturation curves carried out using 3H-Ro 5-4864 (0.4-10 nM) showed significant Bmax decreases in both organs. No significant change in either of these inhibitory activities was observed in the other tissues studied. These data provide support for a role of tribulin in the biochemical response to stress.