Changes in plasma glucose, FFA, corticosterone, and thyroxine in He-O2-induced hypothermia

Unanesthetized, male rats were exposed to normal air (NA), or NA and a 4 h-exposure of He-O2 (79% helium, 21% oxygen) at ambient temperature (Ta) of 22 or - 10 degrees C. Blood samples from each individual were taken from a chronically implanted carotid cannula at 1) preexposure, 2) during exposure, 3) 2.5 h after exposure, and 4) 19-20 h after exposure. Exposure to He-O2 at 22 degrees C caused an increase in plasma free fatty acids (FFA) and corticosterone of 45% and 49%, respectively, with little change in plasma glucose and thyroxine. Exposure to He-O2 at 10 degrees C for 3 h invariably induced hypothermia with body temperature (Tb) decreased to 23.7 +- 0.5 degrees C (N = 10). During hypothermia, plasma glucose, FFA, and corticosterone were significantly higher (P LESS THAN 0.05) than those at preexposure and those after exposure to NA at -10 degrees C. During spontaneous recovery from hypothermia, at Ta = 19 degrees C and NA, glucose, corticosterone, and thyroxine returned to normal, but FFA remained significantly higher than at preexposure. The ability of animals to rewarm spontaneously from hypothermia and the quick return of metabolic substrates and hormones to normal after rewarming indicates the preservation of regulatory mechanisms for metabolism at depressed Tb when hypothermia is induced by He-O2 and cold.

Metabolic and respiratory responses during Helox-induced hypothermia in the white rat

Unanesthetized and unrestrained rats, chronically cannulated in the carotid artery, were exposed to normal air (NA) and Helox (21% O2, 79% He) at ambient temperatures (Ta) of 22 and -10 degrees C. In Helox at Ta = 22 degrees C, the Vo2 was 1.39 ml O2/g-h and the Vco2 0.98 ml CO2/g-h, 145 and 126%, respectively, of the values in NA at Ta = 22 degrees C. The arterial Pao2, Paco2, and pH were comparable in Helox and NA at Ta = 22 degrees C. In Helox at Ta = -10 degrees C, rats invariably became hypothermic after exposure of 0.75 to 1.5 h. During the induction of hypothermia the decrease of Vo2 and Vco2 was oscillatory, Pao2 and pH increased, and Paco2 decreased significatnly (P less than 0.05). Minimum Vo2 and Vco2 during hypothermia averaged 0.71 ml O2/g-h and 0.50 ml CO2/g-h, 23 and 22%, respectively, of the values in normothermic animals at Ta = -10 degrees C. Minimum body temperature during hypothermia was clamped at 21.7 +/- 0.3 degrees C (X +/- SE) by increasing Ta to 19 degrees C. When Helox was replaced by NA, hypothermic rats rewarmed spontaneously, returning to normothermia within 4 h. The data suggest that hypothermia induced by Helox plus cold does not seem to be due to respiratory failure, as systemic hypoxia or hypercapnia were not observed. The controlled hypothermia cycle reported here provides a model for dynamic studies of thermogenic mechanisms both at the normothermic and hypothermic states without the interference of drugs and other nonphysiological treatments.

Behavioral thermoregulation in the pika Ochotona princeps: a field study using radiotelemetry

When either the level or duration of spontaneous activity is increased over an ambient temperature range of 2–28C, the body temperature of the pika shows a slight increase; the maximum fluctuation observed was 1.0C. However, none of the changes in body temperature proved to be significantly different from that of the resting state (P < 0.05).In nature, pikas avoid hyperthermia by means of precise behavioral thermoregulation in which both duration and level of activity are regulated. A negative correlation was observed between the duration of lime spent on the surface of the rocks, and the surface ambient temperature, over a range of 3–27C. Between 0930 and 1930 h, as the surface ambient temperature increased, the percentage of observations in which the pika was below the rocks increased, and vice versa. By engaging in short bursts of surface activity (usually less than a 3.5-min duration) followed by retreat to the cooler microclimate beneath the rocks, pikas are able to regulate their body temperature precisely at a level only 2–3C below the upper lethal temperature.

Adaptation to cold: energy metabolism in an atypical lagomorph, the arctic hare (Lepus arcticus)

Unlike other lagomorphs or any other mammals living in a cold environment, the basal metabolic rate of the arctic hare, Lepus arcticus monstrabilis (0.36 cm3 O2/g per hour) was only 62–83% of the values predicted from its body weight. The minimum thermal conductance (0.010 cm3 O2/g per hour per degree centigrade) was also reduced to only 51–59% of its weight-specific value (0.019–0.017 cm3 O2/g per hour per degree centigrade). The normal body temperature (38.9C), however, was comparable to that of other lagomorphs. The daily energy consumption between ambient temperatures of −24 and 12.5C was between 262 and 133 kcal, which is 6–43% above the minimum resting values at corresponding ambient temperatures.It is concluded that the reduction of surface area to volume ratio and the effectiveness of its insulation are sufficient compensations so that the arctic hare can maintain a normal body temperature with a depressed basal metabolic rate. Such a reduction of metabolism is energetically adaptive for a species living exclusively in a cold and relatively barren habitat.

Soybean polyamines: separation and characterization of cadaverine

Cadaverine in soybeans was separated by ion exchange chromatography from other polyamines previously identified. Identification of cadaverine was based on ion exchange separation, thin layer chromatography, paper electrophoresis, mass and nuclear magnetic resonance spectral analyses. Since the molecules of putrescine and cadaverine are so similar, separation and identification of the two components are difficult. Their R(F) values on thin layer chromatography are close, although cadaverine produces a bluish purple color when sprayed with ninhydrin reagent, while putrescine forms a purple color. Separation likewise is poor by paper electrophoresis, gas chromatography, and gel filtration. The mass spectra of cadaverine and putrescine have m/e peaks at 30, 43, 45, 56, 73, 85, 102 and 30, 43, 59, 71, 88, respectively. The m/e peaks differentiate one compound from the other. Nuclear magnetic resonance spectra and their integration curves show that cadaverine contains two types of methylene protons (10 total) in 3:2 ratio while putrescine produces two types (8 total) in 1:1 ratio. Polyamines occur at levels of micrograms per gram of soybeans with spermidine present in the largest quantity.

Physiology of thermoregulation in the pika, Ochotona princeps

The mean body temperature of pika measured by radiotelemetry under field and laboratory conditions was 40.1 °C (range = 37.9–42.7) over an ambient temperature range of −9.3 to 24 °C. The maximum daily fluctuation in any one individual was less than 2.6 °C and no seasonal difference in the level of body temperature maintained was observed. Hyperthermia and death occurred after a 2-h exposure to ambient temperatures higher than 28 °C, inclusive.The basal metabolic rate was 1.53 cc O2/g h and the thermal conductance was between 0.096 and 0.050 cc O2/gh °C, 143% and 101–53%, respectively, of their predicted weight-specific values. The relatively high body temperature of pika is attributed to its high basal metabolic rate and good insulation. The low thermal conductance, which indicates a reduction of energy consumption at ambient temperatures below the lower critical temperature (21 °C), favors the overwinter survival of this species when only limited food storage is available.

Polyamines in soybeans

Putrescine, spermidine, and spermine were three main polyamines isolated from soybeans and partially characterized. Occurrence of polyamines in soybeans was established by separating trichloroacetic acid extracts of soybeans by cationic exchange column chromatography, identification with thin layer chromatography, paper electrophoresis, mass spectral analysis, reactions with ninhydrin and Dragendorff reagents, and spectrophotometric characteristics. Soybeans contained a minimum of 29.0 micrograms of polyamines per gram of full-fat flour. The alcohol-soluble fraction of soybeans contained polyamines also. Resting seeds contained spermidine in higher concentration than either putrescine or spermine. Spermine appeared to be present in lowest concentration. Preliminary experiments suggested that some polyamines were possibly in bound forms.