Metabolic, respiratory and haematological adjustments of the little pocket mouse to circadian torpor cycles

Abstract

Metabolic, respiratory and haematological parameters were investigated for the Little Pocket mouse during circadian torpor cycles. The rate of O 2, consumption decreased from 7.04 to 0.05 ml O 2· g −1· hr −1, with a corresponding decrease in respiratory minute volume from 49.4 to 0.9 ml · min −1 during torpor at an ambient temperature of 10 C. No changes in haemoglobin concentration (19.7 g/100 ml), haematocrit (54 %), red blood corpuscle count (12.4 10 6/μl), mean corpuscular volume (43.6 μm 3), mean corpuscular haemoglobin content (16.2 pg), mean corpuscular haemoglobin concentration (37.4 %) and [2,3-DPG] (9.6 μmol/g Hb) were observed during torpor cycles. The half saturation tension of P. longimembris haemoglobin was 41 mm Hg (37 C, pH = 7.28) and 19.7 mmHg (10 C, pH = 7.51).The effect of temperature on P 50was Δlog P 50/ C = + 0.0106(pH = 7.4). Venous blood parameters were: euthermic mice (37 C); P CO 2 = 36.8 mm Hg, P O 2 = 49.5 mm Hg, pH = 7.28,[HCO 3 −] = 17.3mmol/l ; torpid mice (10 C) ; P CO 2 = 14.6,P O 2 = 35.7,pH = 7.51,[HCC3] = 18.8. These data indicate a new, relatively acidotic acid-base status during torpor, characterised by a higher H +/OH − ratio. The respiratory sensitivity to inspired CO 2 of pocket mice was, despite their being semi-fossorial, typical of other mammals. High concentrations of CO 2, did not induce, or facilitate, entry into torpor.