Effect of biogenic amines on the contractile activity of visceral muscles in the beetle Tenebrio molitor

Biogenic amines are biological active compounds that play a significant role in regulation of animal physiology. In insects, the main amines are trace amines like octopamine and tyramine. Those two amines seem to be a partial counterparts of epinephrine and norepinephrine present in vertebrates. Little is known about activity of those compounds in beetles, hence we examined effects of 4 amines on the heart, hindgut and oviduct contractile activity of Tenebrio molitor L. (Coleoptera Tenebrionidae). The results showed that in vivo tyramine and octopamine caused a cardioinhibitory effect on 0-1-day old pupae and similar effects of these compounds were observed in vitro in adults beetles. Dopamine decreased weakly the frequency of heart rate in pupae but increased it in adult beetles at the highest concentration tested while epinephrine caused no changes in both stages. Tyramine and octopamine showed dose-dependent and organ-specific activity on T. molitor hindgut and oviduct. In vitro, they inhibited contractile activity of hindgut whereas on oviduct they acted as myostimulators. Dopamine and epinephrine caused stimulation of contractile activity of muscles of both organ studied. The pharmacological experiments suggest possible modulation of an endogenous mechanism generating muscle contractions via the adrenergic system and indicate the presence of adrenergic receptor(s) in the visceral organs of the beetle T. molitor.