The occurrence and functions of ultradian rhythms

Area of Science:

• Chronobiology
• Biochemistry
• Physiology

Background:

• Ultradian oscillations (periods 5 min - 4 h) are observed in various biological systems, from cell-free extracts to whole organisms.
• While some systems like glycolysis may rarely show ultradian behavior in vivo, others in lower eukaryotes function as timekeeping rhythms.
• Ultradian rhythms in oxygen consumption and carbon dioxide production (10 min - 20 h) are documented in endotherm animals, influenced by environmental and other biological rhythms.

Purpose of the Study:

• To explore the prevalence and potential functions of ultradian rhythms in biological systems.
• To investigate the endogenous and genetic basis of these rhythms.
• To propose a role for temporal organization in optimizing organismal maintenance and adaptation.

Main Methods:

• Literature review and synthesis of existing studies on ultradian oscillations.
• Analysis of data from cell-free extracts, single-celled eukaryotes, cultured cells, embryos, and endotherm animals.
• Comparative analysis across species and strains to infer endogenous and genetic origins.

Main Results:

• Ultradian oscillations are widespread, occurring in diverse organisms and biological contexts.
• In lower eukaryotes, ultradian rhythms appear to serve timekeeping functions.
• In endotherm animals, ultradian rhythms in gas exchange are influenced by environmental factors and other biological rhythms.
• Interspecies and interstrain variations strongly indicate an endogenous, genetic basis for these rhythms.

Conclusions:

• Ultradian rhythms are fundamental biological phenomena with likely timekeeping roles.
• These rhythms are endogenously controlled and have a genetic basis.
• Temporal organization via ultradian rhythms optimizes physiological processes for thermodynamic maintenance and adaptation.
• Ultradian rhythms contribute to an organism's ability to adapt to environmental fluctuations and may play a role in genetic selection.