Mario Rosenmann

Seasonal Changes in the Metabolic Capacity of Red-Backed Voles

By the use of helium-oxygen mixtures it is possible to elicit maximum metabolic effort from small mammals under modest cold stress without training or injury. By this means, levels ranging from 5 to 8 times the standard metabolism (met) have been observed in various captive rodent species. These values are lower than those of 15 to more than 20 met observed in larger mammals such as dogs, man, and horses which can be systematically trained to exercise (Rosenmann and Morrison 1974). However, wild individuals may have greater metabolic demands at times, particularly in winter. The present study examines the influence of seasonal cold on unconfined individuals of a subarctic species in its natural habitat. Besides the maximum metabolism (Mmax), other bioenergetic parameters of interest include body temperature (TB), basal metabolism (MB), thermal conductance (C), low lethal temperature [TB (Mmax/C)], low critical temperature [TB (MB/C)], metabolic expansivity (MmaxMB), and metabolic reserve (Mmx M).

Metabolic response of highland and lowland rodents to simulated high altitudes and cold

Abstract 1. 1. The metabolic response to hypoxia at moderate O 2 demand was measured in seven highland and fifteen lowland species and races of small mammals. 2. 2. The critical ambient p O 2 for reducing O 2 uptake was lower in the highland group (110 vs 122 torr). 3. 3. Below this p O 2 the further metabolic reduction was also lower in the highland group (0·49 vs 0·75%/torr). 4. 4. The metabolic expansivity at 755 torr O 2 was larger in the three highland species tested than in four lowland ones (4·0 vs 2· met), representing a reduction in the normoxic maximums of 36 vs 54 per cent. 5. 5. In normoxia the respiratory frequency for both highland and lowland species followed the function W −0·21 . The hypoxic increase of respiratory frequency at a p O 2 of 68 torr was lower in the highland forms (35 vs 81 per cent).

Oxygen uptake and temperature regulation of young harbor seals (Phoca vitulina richardi) in water.

Abstract o 1. Oxygen uptake and body temperatures were measured in two young harbor seals at water temperatures between 5 and 37°C. 2. Basal metabolic rates of both animals were approximately 0·74 u O2g−1hr−1 or about 2·6 times the value expected for an adult terrestrial mammal of the same weight. Lower critical temperature was 12°C in one animal and 19°C in the other. 3. A surprising tolerence to high water temperatures was demonstrated and thermal and metabolic equilibrium could be established with only a 2°C difference between deep body and water temperature. 4. It is concluded that water at temperatures typically encountered by newborn of the northern harbor seal imposes only a modest cold stress requiring, at most, a 2-fold increase in metabolism over the basal rate.

Seasonal sympatho-adrenal and metabolic responses to cold in the Alaskan snowshoe hare (Lepus americanus macfarlani)

Abstract 1. 1. Winter-acclimatized snowshoe hares achieved a significantly greater maximum metabolic response to cold (Mmax) than summer hares. 2. 2. Summer hares exposed to +13°C and winter hares to −20°C excreted similar levels of urinary norepinephrine (NE) and epinephrine (E). 3. 3. Cold exposure of summer hares to −20°C and winter hares to −45°C (conditions which elicit the same metabolic rate in both groups) caused significantly greater NE and E excretion in summer hares. 4. 4. The results suggest that seasonal acclimatization involves enhanced non-shivering thermogenesis, increased sensitivity to NE and increased Mmax in winter hares which enables retention of a constant annual metabolic range for activity.

Metabolic level and limiting hypoxia in rodents.

Abstract 1. 1. Limiting (lethal) values for pO2 (Pc) ranging from 15 to 44 torr were measured at thermoneutrality for eighteen rodent species, 2. 2. The final level of oxygen consumption (M) showed a direct relationship: Pc = 27 M Deviations from this mean curve reflect transport effectiveness with indices ranging from 0·029 to 0·050 met/torr (1 met = 3·8W0·73 cm3 O2/hr). 3. 3. Four highland species suppressed their metabolism under hypoxia (0·56–0·74 met) and showed corresponding low critical values (15–21 torr). 4. 4. Pyrogenic agents (2, 4-DNP) increased both metabolism and Pc.

Some effects of water deprivation in reindeer.

MAMMALS living in hot, dry climates show adaptations in terms of temperatu e regulation and water balance as compared to mammals from temperate regions. Thus, when dehydrated, the camel allows its body temperature to rise rather than evaporate water to dissipate heat, and also spares the circulating plasma at the expense of tissue water (Schmidt-Nielsen et al., 1957). The guanaco, however, regulates its temperature closely under heat stress despite severe dehydration and only maintains the fluidity of the circulating medium by virtue of the close packing of hemoglobin in the erythrocytes (Rosenmann and Morrison, 1963). Sheep and cattle in tropical or hot, arid lands are adapted to heat as compared to their temperate relatives (Macfarlane, 1964). The question may now be asked: What is the response to dehydration and heat in arctic forms whose primary adaptation may be toward severe winter cold? Ungulates in the arctic and subarctic seem always to have abundant water, and only rarely to be exposed to high ambient temperature. However,

Thermoregulation in the Testes of Octodon degus: A Nonscrotal Rodent

In the rodent Octodon degus the testes are located inside the abdomen even during the breeding season, and their temperature is only 0.9 C lower than body temperature (36.8 C). The cauda epididymides are located in the cremasteric sacs, and their temperature is 4.8 C lower than body temperature even though they are in a nonscrotal position. Compared to the testes, the cauda epididymides are insulated from body core and are more thermally conductive to the environment. Factors reducing thermal conductance from body core to cauda epididymides are the location of the cauda epididymides outside the abdominal cavity in the cremasteric sac, a fat body interposed between the cauda epididymis and the body core, and a reduced blood supply. The higher conductance of the cauda epididymides to the environment is mainly due to their location under a perianal circle, a region devoid of hair with a greater thermal conductance than adjacent regions covered by hair.