[Melatonin effect on the regeneration of the flatworm Girardia tigrina].

ABSTRACT

The melatonin effect on the anterior and posterior ends of a free-living flatworm Girardia tigrina was studied, as well as the variability of the mitotic activity of the stem cells (neoblasts) in the anterior and posterior postblasteme. This hormone may inhibit the regeneration of the anterior end of the animal in the physiologic-friendly concentrations of 10(-10)-10(-15) M by suppressing the mitotic activity of the neoblasts. This hormone does not affect the posterior end's regeneration; thus, its regeneration effect is significantly elective.