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Mitotic Activity in Mice is Suppressed by Energy Restriction-Induced Torpor¹

Akio Koizumi, Mikako Tsukada, Yasuhiko Wada, Hirotake Masuda^* and Richard Weindruch

Department of Hygiene ^* Department of Pathology, Akita University School of Medicine, Akita 010, Japan Department of Medicine, University of Wisconsin, Madison, WI 53706

We monitored core body temperatures by telemetry in energy-restricted (201 kJ/wk) and control (397 kJ/wk) C57BL/6 and SHN/C3H F1 mice to determine whether torpor may be involved in the suppression of mitotic activities resulting from energy restriction. The energy restriction regimen employed inhibited the development of cancer and greatly extended longevity in both these mouse strains. Male and female C57BL/6 mice subjected to energy restriction from 4 wk of age and tested at 3 mo of age became torporific (body temperature <31°C) at ambient air temperatures of 20–22°C, whereas control animals stayed euthermic (>35°C). Energy restriction also induced torpor in 3- and 13-mo-old SHN/C3H F1 female mice, whereas 3-, 13- and 24-mo-old control mice were euthermic. Energy restriction decreased mitotic activities to 30% of control values in both jejunum and epidermis in 3-mo-old female C57BL/6 mice maintained at 20–22°C. However, this suppression of mitotic activities was antagonized by housing the energy-restricted mice at 30°C for 2 wk, indicating that torpor plays a substantial role in suppressing mitotic activities in energy-restricted mice.

KEY WORDS: • mice • energy restriction • torpor • mitotic activity

¹ Supported by grants from the Ministry of Education and Welfare of the Japanese Government (no. 03670259, 1991), the Uehara Memorial Foundation, 1992 and Choju Kagaku to A. K., and from the American Cancer Society (no. CN-57) to R. W.

Manuscript received 27 December 1991. Revision accepted 28 February 1992.

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