Ventilatory and metabolic responses to hypoxia in the smallest simian primate, the pygmy marmoset

Milsom

2003

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SUMMARY The hypoxic metabolic response of mammals involves a reversible metabolic suppression, possibly brought about by a reduction in the body temperature set-point. In the present study we tested the hypothesis that this is accompanied by a transient increase in heat loss that facilitates the decline in body temperature and metabolic rate. Peripheral heat distribution was assessed using infrared thermography to measure the surface temperatures of the golden-mantled ground squirrel at three different ambient temperatures (10, 22 and 30°C). During early hypoxic exposure, surface temperatures increased dramatically in the feet, ears and nose, and this increase was more dramatic and prolonged at 22°C than at the other two temperatures. These increases were associated with a fall in metabolic rate. Following this initial increase, surface temperatures decreased back to control values, and at 10°C, the surface temperatures of the eyes and body decreased below normoxic levels. Subsequent normoxic recovery was not accompanied by transient changes in surface temperatures, despite large increases in metabolic rate associated with post-hypoxic shivering and thermogenesis. The temporal changes in surface temperature suggest that peripheral blood flow is initially increased during hypoxia, shifting heat away from the core to the periphery and thus facilitating cooling. These results are consistent with the hypothesis that hypoxia leads to a regulated fall in body temperature.

Section: Co∑supporting

confidence: 80%

Transient peripheral warming accompanies the hypoxic metabolic response in the golden-mantled ground squirrel

Milsom

2003

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“…In other words, oxygen impacts differently on the various thermoregulatory pathways in the bumblebee and thermolysis occurring prior to metabolic downregulation. This situation is similar to what has been observed in small mammals (Tattersall et al, 2002;Tattersall and Milsom, 2009). Exposure to low O 2 levels, however, does not appear to have a long-term consequence in terms of thermoregulatory ability.…”

Section: Effects Of Oxygen On Body Temperaturesupporting

confidence: 91%

Fluctuations in oxygen influence facultative endothermy in bumblebees

Dzialowski

Nicol

et al. 2014

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Bumblebees are facultative endotherms, having the ability to elevate thorax temperature above ambient temperature by elevating metabolism. Here, we investigated the influence of hypoxia on metabolic demands and thermoregulatory capabilities of the bumblebee Bombus terrestris. We measured thorax temperature, rates of oxygen consumption and carbon dioxide production, and abdominal pumping rates of bees randomly exposed to oxygen levels of 20, 15, 10 and 5 kPa at 26°C. Under normoxia, bumblebees maintained an elevated mean thorax temperature of 35.5°C. There was no significant change in thorax temperature at 15 kPa O 2 (33.4°C). Mean thorax temperature decreased significantly at 10 kPa O 2 (31.6°C) and 5 kPa O 2 (27.3°C). Bees were able to maintain an elevated metabolic rate at 15 and 10 kPa O 2 . In normoxia, endothermic bees exhibited periods of rapid abdominal pumping (327 min −1 ) interspaced by periods of no abdominal pumping. At 10 kPa O 2 , abdominal pumping rate decreased (255 min −1 ) but became more continuous. Upon exposure to 5 kPa, metabolic rate and abdominal pumping rate (152 min −1 ) decreased, although the animals continued abdominal pumping at the reduced rate throughout the exposure period. Bumblebees are able to meet the energetic demands of endothermy at 15 kPa O 2 , but become compromised at levels of 10 kPa O 2 and below.

“…Animals from the summer phase showed a hypoxic response similar to that observed in other mammals; decreases in metabolic rate and T b in hypoxia became larger as T a and oxygen levels decreased (Hiestand et al, 1950;Wood, 1995;Barros et al, 2001;Tattersall et al, 2002;Scott et al, 2008). The relationship between T a , metabolic rate and T b is consistent with a reduction in thermogenesis in hypoxia, accompanied by a selection of lower temperatures, leading to a temperature-dependent decrease in T b .…”

Section: Discussionsupporting

confidence: 71%

“…Hibernating species are known to survive periods of anoxia for longer than nonhibernating species (Lutton, 1982) and have a more moderate physiological response when confronted with a hypoxic stress (Faleschini and Whitten, 1975). A common hypoxic response that small mammals and other vertebrates exhibit, whether they hibernate or not, is a rapid and reversible decrease in body temperature (T b ) and metabolic rate (Wood, 1995;Wood and Gonzales, 1996;Tattersall et al, 2002;Tattersall and Milsom, 2003). The higher tolerance to hypoxia in hibernators does not necessarily dictate the magnitude of this thermoregulatory response to hypoxia.…”

Section: Introductionmentioning

confidence: 99%

Seasonal changes in thermoregulatory responses to hypoxia in the Eastern chipmunk (Tamias striatus)

Levesque

2009

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SUMMARYMammalian heterotherms are known to be more tolerant of low oxygen levels than homeotherms. However, heterotherms demonstrate extreme seasonality in daily heterothermy and torpor expression. Because hypoxia depresses body temperature (T b ) and metabolism in mammals, it was of interest to see if seasonal comparisons of normothermic animals of a species capable of hibernation produce changes in their responses to hypoxia that would reflect a seasonal change in hypoxia tolerance. The species studied, the Eastern chipmunk (Tamias striatus, Linnaeus 1758), is known to enter into torpor exclusively in the winter. To test for seasonal differences in the metabolic and thermoregulatory responses to hypoxia (9.9 kPa), flow-through respirometry was used to compare oxygen consumption, minimum thermal conductance and T b under fixed ambient temperature (T a ) conditions whereas a thermal gradient was used to assess selected T a and T b in response to hypoxia, in both summer-and winteracclimated animals. No differences were observed between seasons in resting metabolism or thermal conductance in normoxic, normothermic animals. Providing the animals with a choice of T a in hypoxia attenuated the hypoxic drop in T b in both seasons, suggesting that the reported fall in T b in hypoxia is not fully manifested in the behavioural pathways responsible for thermoregulation in chipmunks. Instead, T b in hypoxia tends to be more variable and dependent on both T a and season. Although T b dropped in hypoxia in both seasons, the decrease was less in the winter with no corresponding decrease in metabolism, indicating that winter chipmunks are more tolerant to hypoxia than summer animals.