Metabolism and ventilation in acute hypoxia: a comparative analysis in small mammalian species

Abstract

O2 consumption (VO2), CO2 production (VCO2), and minute ventilation (VE) have been measured during normoxia and hypoxia (10-20 min in 10% O2) in specimens of 27 species from 6 mammalian orders, ranging in body mass (M) from a few grams to several kilograms. In normoxia, both metabolism and VE scaled close to M3/4, VE/VO2 and VE/VCO2 therefore being independent of M. In hypoxia, VE/metabolism increased in all species (on average greater than 100%), mostly because of a drop in VO2. On average, VE was 23% above the normoxic value but in some species decreased below normoxia. VO2 dropped in all but one species, on average 35%. Body temperature decreased by variable amounts, usually more in the smallest species. The decrease in metabolism during hypoxia was positively correlated with the resting metabolic rate of the species in a manner very similar to what can be calculated from data of previously studied newborn mammals. Hence hypoxia may decrease metabolic rate by decreasing thermogenesis, with larger effects in smaller animals, whether newborns or adults, because of their higher thermogenic requirements. We conclude that 1) hypoxic hypometabolism is a general characteristic of the mammalian response to hypoxia and cannot be neglected in the interpretation of ventilatory and cardiovascular responses and 2) its magnitude is inversely related to the resting VO2 of the species and therefore could be less prominent or possibly absent in adults of larger species.

Adenosine receptors mediate the hypoxic ventilatory response but not the hypoxic metabolic response in the naked mole rat during acute hypoxia

“…Furthermore, we utilized a smaller chamber with a lower flow rate than the earlier study, which would reduce the rate of animal-generated heat loss from the chamber via thermal convection. To our knowledge, naked mole rats are the only mammals studied to date that exhibit such a robust metabolic depression in acute hypoxia without a concomitant decrease in T b and entry into a torpor-like state [34]. These unique responses may be due to the warm and consistently hypoxic environment in which naked mole rats live.…”

“…(c) The naked mole rat hypoxic ventilatory response is mediated by adenosine receptors Naked mole rats exhibit a robust decrease in _ V E when exposed to hypoxia for 1 h, which is atypical of mammals [4,34]. Instead, a hypoxia-mediated increase in _ V E is rspb.royalsocietypublishing.org Proc.…”

Circadian pattern of ventilation during acute and chronic hypercapnia in conscious adult rats

“…V O2 was measured by the open-flow method (11). The inflowing and outflowing gas concentrations were monitored by a calibrated polarographic O2 analyzer (OM-11, Beckman) and by an infrared CO 2 analyzer (CD-3A, Applied Electrochemistry or LB-2, Beckman).…”

NMDA receptor-mediated modulation of ventilation in obese Zucker rats

“…Oxygen consumption (V Ç O 2 ) and carbon dioxide production (V Ç CO 2 ) was calculated from the difference between O 2 and CO 2 in¯ow and out¯ow multiplied by the gas¯ow, neglecting the small error introduced by the respiratory quotient less than unity. 21 Data are presented at standard temperature and pressure under dry conditions (STPD), corrected for the effective body mass and expressed in kilograms (kg) to the power of 0.75 (ml O 2 STPD kg 0.75 min 71 ). 22 Effective body mass (EBM) was calculated as 1.00 M 0.75 and 0.86 M 0.75 for lean and obese animals respectively.…”