Heavy water slows biological timing processes

Abstract

Deuterium oxide lengthens the period of the endogenous tidal activity rhythm of the sand-beach isopod, Excirolana chiltoni. Heavy water has also been shown to retard the circadian rhythm of deer mice, when added to the animals' drinking water. The average dosage dependence of the effect can be estimated with high precision for both isopod and mouse, and the two values are indistinguishable. A similar slowing of circadian rhythms, due to D2O, has also been reported for an alga, a higher plant, two species of birds and three other rodents. Although data permitting reliable estimates of dosage dependence have not been published for these latter cases, the effect is apparently also of about the same magnitude. This evidence suggests fundamental similarities in the rhythmic mechanisms. Heavy water also produces a reversible slowing of several biological rhythms with periods in the millisecond range: the electric-organ discharge of a gymnotid fish (Stenarchus albifrons); the respiratory cycle of goldfish, as well as of an amphipod (Paraphoxus) and an isopod (Excirolana); and the cardiac cycle of a clam (Donax) and a crab (Emerita). Since these high-frequency rhythms originate in pacemakers dependent on diffusion processes, the experimental results suggest the possibility that long-period biological clocks are also based on diffusion-dependent pacemakers.