Seasonal Changes in Heart Weights of Wild Wood Mice Apodemus speciosus

Abstract

Total 182 wild wood mice, Apodemus speciosus, were collected with snap traps during the period from August 1981 to January 1983 at Miasa village (alt. 830 m) in Nagano Prefecture. Their hearts were dissected and separated into the right (RVW) and the left (LVW) ventricular walls. Ratio of the right ventricular weight against the total ventricular weight (RVW/TVW) was obtained and used as an index of the right ventricular hypertrophy. The values seemed to be related to the seasonal changes of air temperature in the animal habitat.
The results are as follows : TVW, LVW, RVW and RVW/TVW of the wood mice collected in late autumn and winter were apparently greater than those collected in summer. From this study, it became clear that the cause of hypertrophy in cold seasons was the ventricular hypertrophy in both sides, particularly, hypertrophy was more progressed in the right ventricles.
Those changes of weight are considered to be a physical aspect caused by the metabolic adaptation to the seasonal temperature changes, especially to the low temperature in late autumn and winter.