Cardiorespiratory and metabolic reactions during entrance into torpor in dormice, Glis glis

Abstract

Dormice voluntarily enter torpor at ambient temperatures ranging between 0-28°C. This study describes heart rate, ventilation frequency, O 2 -consumption (defined as metabolic rate), CO 2 -production and body temperature during entrance into torpor. Their temporal relationship was analysed during the time course of metabolic depression at different ambient temperatures. Body temperature and heart rate were measured in unrestrained dormice with implanted transmitter. Ventilation frequency was monitored by total body plethysmography or infrared video monitoring. To compare entries into torpor at different T a these periods were distinguished into four different phases: the resting phase prior to torpor, the phase of pre-torpor adjustments, the reduction phase and the phase of steady state torpor. In the pre-torpor phase, dormice increased their ventilation, metabolic rate and heart rate, indicating that the torpid state is initiated by an enhanced metabolic activity for about an hour. This was followed by a rapid reduction of ventilation, metabolism and heart rate, which reached their minimum values long before body temperature completed its decline. The results of the present study show that the entrance into torpor is caused by an active respiratory, cardiac and metabolic depression.

Metabolic Flexibility: Hibernation, Torpor, and Estivation

“…However recent studies demonstrate significant temperature-independent suppression of mitochondrial oxidative metabolism in daily torpor (40,167). Moreover, there are significant reductions in MR during fasting-induced daily torpor in golden spiny mice (Acomys russatus) at thermoneutral temperatures with virtually no change in T b (123), a similar result to earlier studies on the edible dormouse, Glis glis (90). Under these conditions, thermogenic metabolism should be minimal, but during entrance, MR declines below basal levels even before T b falls.…”

Heart rate as a predictor of metabolic rate in heterothermic bats

“…Minimum mean f H (8 beats min −1 ) in particular was well below values reported for unrestrained northern hemisphere bats of a similar mass (40 beats min −1 ) (Kulzer, 1967). Moreover, the absolute minimum of 5 beats min −1 was similar to that measured in much larger hibernators such as woodchucks (Marmota monax, 3-5 kg) (Lyman, 1958) and dormice (Glis glis, ~150 g) (Elvert and Heldmaier, 2005).…”

Integrative Physiology of Fasting

“…For birds and mammals that experience hibernation or daily torpor, entrance into torpor is accompanied by reductions in cardiac, ventilatory, and metabolic activity and a subsequent fall in T b that lags behind these parameters (151,208,232,255,526). However, after metabolism is actively suppressed by cardiopulmonary and metabolic adjustments, the passive fall in T b likely contributes to further reductions in metabolic rate until a minimum T b is reached (208,255).…”