Relationships between Respiratory Quotient and Metabolic Rate during Entry to and Arousal from Daily Torpor in Deer Mice (Peromyscus maniculatus)

Abstract

Retention ofCO2 and respiratory acidosis have previously been reported to accompany entrance to hibernation, with acid-base and CO, balance returning to normal upon arousalfrom hibernation. The present study indicates that these alterations are not limited to species which have the ability to undergo deep hibernation, but are also involved in another mammalian dormancy state, daily torpor. Deer mice (Peromyscus maniculatus) were used to examine the time course of changes in respiratory quotient (RQ), metabolic rate (MR), and body temperature (Tb) during daily torpor at an ambient temperature of 10" C For several hoursprior to daily torpor, RQ steadily declinedfrom 0.92 to 0. 74, indicating a shift in primary metabolic substratefrom carbohydrate tofat, while MR andTb remained constant at 4.23 + 0 44 mL 02/g . h and 36 6' + 0. 9" C, respectively. Entrance to daily torpor involved a transitory decrease in RQ (0. 74-0 63-0 73) that lasted less than 12 min and reflected C02 retention and accompanying respiratory acidosis. This was subsequentlyfollowed by a rapid drop in MR andTb. Respiratory quotient remained stable during steady-state torpor (0. 74 0. 02). Metabolic rate and Tb in daily torpor were 1.12 + 0. 35 mL O/g . h and 21. 6' 1. 6 C, respectively. A transitory increase in RQ (0. 76-0.96-0. 76) was associated with arousal, signifying release of the excess C2O,, with MR and then Tb increasing after the RQ change. The order of change in the measuredparameters suggests that adjustments in the CO, content of the body contribute to the induction and termination ofdaily torpor in deer mice.

Pathophysiology of white-nose syndrome in bats: a mechanistic model linking wing damage to mortality

“…Dehydration and hypovolaemia can cause metabolic acidosis due to anaerobic lactic acid production in tissues with reduced blood flow. Plasma pH was not significantly reduced with infection probably owing to buffering by bicarbonate and the quick response by peripheral chemoreceptors to acidosis triggering an increase in respiration rate to off-load CO 2 [19]. This is consistent with the decreased pCO 2 we observed.…”

Hibernating above the permafrost: effects of ambient temperature and season on expression of metabolic genes in liver and brown adipose tissue of arctic ground squirrels

“…RQ levels can be depressed as CO 2 accumulates in the blood during torpor re-entry (e.g. Malan et al, 1985;Nestler, 1990), but we are unaware of a mechanism for shifts in P CO2 that could cause prolonged increases in RQ throughout steady-state torpor maintained over several weeks.…”

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

“…Bickler (1984) and Malan (1988) observed that the entrance into daily torpor or hibernation is accompanied by a falling respiratory exchange rate und suggested that this contributes to a CO 2 retention. Drops of RQ at the beginning of entry into torpor have been observed for several other species (Snapp and Heller, 1981;Bickler, 1984;Malan, 1986;Nestler, 1990). Hence, inhibitory effects of CO 2 retention and respiratory acidosis on thermoregulatory structures, glycolysis, neural activity and brown fat thermogenesis have been discussed .…”