Supplemental melatonin increases clonal lifespan in the protozoan Paramecium tetraurelia.

The hypothesis that melatonin supplementation can increase the lifespan of a single-celled organism was tested by the administration of melatonin to the ciliated protozoan Paramecium tetraurelia. Melatonin supplementation in dim red light at a dose of 0.043 mM (10 mg/L) of nutrient media (bacterized Cerophyl) per day, followed by incubation for 23 hr in darkness, increased the mean clonal lifespan of Paramecium tetraurelia in days by percentages ranging from 20.8% (P < 0.01, two-tailed t-test) to 24.2% (P < 0.01, ANOVA) over controls. Maximum clonal lifespan in days was also increased in melatonin-supplemented cells, from 14.8% to 24.0% over controls. Mean clonal lifespan in fissions was not significantly greater in melatonin-supplemented cells, with values ranging from 6.0% to 15.5% over controls. Maximum clonal lifespan in fissions did not differ appreciably, with values ranging from 1.0% to 9.1% over controls, except in the case of cells selected for rapid division rates, in which melatonin-supplemented cells (393 fissions) lived 20.9% longer than controls (325 fissions) in terms of cumulative cell doublings during the clonal lifespan. The finding that melatonin supplementation increased clonal lifespan in Paramecium tetraurelia, an aerobic, single-celled organism, suggests that the mechanism of melatonin's longevity-promoting effects may be intracellular.