Period Of Cold Exposure Research Articles

Comparative effects of temperature exposure on mass and oxidative enzyme activity of brown fat in insectivores, tupaiads and primates.

AbstractA study has been made to see if hyperplastic and biochemical responses similar to those which occur in temperature‐exposed rodents also occur in insectivores, protoprimates and primates. Representative insectivores included the shrewsSuncus murinus andCryptotis parva. The representative prottoprimate wasTupaia chinensis. The representative primate wasMacaca mulatta. Both shrews show a striking thermogenic response in the brown fat with respect to increased specific activity of α‐glycerophosphate oxidase and succinoxidase.Suncus also showed an increase in brown fat mass following cold exposure. In both shrews cold caused the brown fat to become darker in color.Cryptotis did not show a significant increase in brown fat mass, but this may be due to the fact that the cold exposure period was only four days. Thus the shrews appear to be rodent‐like with respect to effects of cold on brown fat. In the Tupaiads the ratio of brown fat to body weight is not nearly as high as in rodents nor is there a striking hyperplasia with cold exposure. Thus the brown fat would seem to be of less importance to the Tupaiads than to rodents and shrews and the Tupaiads appear to be intermediate in this respect between the insectivores and the true primates. AdultMacaca, in spite of eight months of cold exposure at about 4–6 C, showed no hyperplasia of the brown fat and no increase in oxidative enzyme levels. Thus in adult primates so far studied, the evidence indicates that brown fat does not play an important role in homeothermy as it does in rodents.

Effect of varying periods of cold exposure on the action and metabolism of hexobarbital

This study compares the hypnotic effect of hexobarbital with its rate of metabolism in vitro in the rat exposed to cold (5°) for varying periods of time. Whereas the 25° control rats showed a decrease in sleep time that was most pronounced after 1–3 weeks of exposure and which corresponded with an increased rate of metabolism, the cold-exposed rats showed longer sleep times than their age-matched controls as early as 3 days after exposure which persisted for the 7 weeks of the experiment. The rate in vitro of hexobarbital metabolism of the cold-exposed groups did not vary significantly from the zero day control level during the entire experiment. Brain levels of hexobarbital upon awakening were the same for control rats as for rats exposed to 5° for 3 days. A seasonal effect to the hypnosis is suggested, since rats subjected to 3 days of cold exposure in April exhibited a changed dose-response curve from that of their warm controls, but this did not occur for similar groups tested in November.

Calculation of mean body temperature.

Four young male subjects were exposed for 1 h to environmental temperatures of 8.5 °C, 14.0 °C, and 20.0 °C while lying on a rope mesh cot. During exposure they wore swimming trunks only. Heat production, skin temperature at seven locations, and rectal temperature were measured. Mean body temperatures (MBT) and heat debts were calculated from Burton's equations and also from equations determining radiative, convective, and evaporative heat losses. It was found that a linear equation with constant coefficients, such as Burton's, for measuring MBT does not allow for the fact that in the non-steady state the body continues to lose heat even though the skin temperature is relatively constant. During the initial period of cold exposure the coefficient of skin temperature when calculating MBT should be much smaller than at later stages in the cooling.

Effect of a short period of cold exposure on plasma FFA level in lean and obese humans

Plasma FFA level rose in normal weight control and to a lesser degree in obese women when they were exposed to cold at 4–6°C for a period of 30 minutes. This rise, in lean subjects, of plasma FFA was eliminated by pretreatment with either nicotinic acid or propranolol. The response to cold was a biphasic one with an early fall in plasma FFA level followed by a rise. The rise in plasma FFA appears to be catecholamine induced, and the absence of significant change in blood glucose would suggest that norepinephrine may be the stimulus. The biphasic nature of the response to cold suggests a favoring of utilization to mobilization of FFA early and the reverse later. The difference in the response noted in obese women may represent a decreased responsiveness, but possibly may be due to an insulating effect of adipose tissue mass.

Effect of cold exposure on serum lipids and lipoproteins in the rat.

The effect of cold exposure for 1–52 days on the concentration and composition of the serum lipids and lipoproteins in male Wistar rats was studied. Serum lipoproteins were separated by preparative ultracentrifugation into three density classes, very low density (d < 1.006), low-density (d, 1.006–1.070), and high-density (d, 1.070–1.218). On the first day of cold exposure, total serum lipids were reduced by 20–25%, this decrease occurring mainly in the triglyceride fraction. Although the low-density and high-density lipoproteins were not affected by cold exposure, the concentration of the very low density lipoproteins fell markedly to 70–75% below normal levels. These alterations in the pattern of serum lipids and lipoproteins persisted throughout the cold-exposure period. Sex or prior feeding of a high-fat, high-carbohydrate, or high-protein diet did not modify these cold-induced changes. The response of the very low density lipoproteins to cold was immediate and rapid, the rate and degree of change being greatest in the first 4 hours of exposure. Conversely, the recovery of the very low density fraction to normal after removal of the rats from the cold was slow and depended upon the period of prior exposure. Animals exposed to 4 °C for 4 days required 3 days at 22 °C for the very low density lipoproteins to return to normal, and the recovery period was twice as long for cold-acclimatized (4 weeks) animals. The role of the triglyceride-rich very low density lipoproteins as a readily available energy source in the animals is discussed in the light of these results.

AN ANALYSIS OF DNA LOSS AND SYNTHESIS IN THE RAT ADRENAL MEDULLA NUCLEI UPON COLD STIMULATION

The peculiar changes previously observed in DNA content of rat adrenal medulla cell nuclei upon intermittent cold exposure (15 hr at +4 degrees C followed by 9 hr at room temperature) have been further studied with the aid of Feulgen histophotometry and H(3)-thymidine radioautography. The amount of DNA decreases progressively with increasing length of cold exposure until 300 hr (-32%). Later a rapid change takes place, whereby DNA content per nucleus returns to values which are slightly, but consistently lower than normal. At termination of a period of cumulative exposure to cold, an analysis of a whole-day experimental cycle shows that the DNA decrease is due to loss of DNA during cold exposure and that DNA synthesis occurs upon return to room temperature. The balance between these two processes can be divided into three stages: (a) loss of DNA up to 300 hr of cumulative cold exposure; (b) marked increase in DNA by 350 hr; (c) oscillation around zero or slightly negative at 400 hr and beyond. These variations are due to: (1) the extension of DNA synthesis into the period of cold exposure as clearly demonstrated by radioautography (stage b), and (2) a later still greater DNA loss (stage c) which partly offsets the increased synthesis. A complex pattern of adaptation of the adrenal medulla cells, as regards DNA content, to the repetitive cold stimulus is thus demonstrated.

VARIATION OF PLASMA KETONES AND FREE FATTY ACIDS DURING ACUTE COLD EXPOSURE IN MAN.

We have studied the magnitude of ketosis induced during acute cold exposure. Plasma and urinary ketone bodies and plasma free fatty acids (FFA) were followed in four healthy young men at rest during a 90-min period of seminude exposure to 0 C in still air. This period was followed by 4 hr of recovery at 25 C. Each subject served as his own control throughout an experimental sequence in which one cold-exposure and corresponding control period (25 C) were experienced each week for 3 successive weeks. The subjects were in a fasting state but with water ad libitum beginning 12 hr prior to the experiment. Light weight clothing was worn during recovery and control periods. The combined group data show a significant increase in plasma FFA during cold exposure as compared with similar control periods. Although true hyperketonemia or hyperketonuria did not develop, the levels of plasma ketones are elevated in the cold-exposure period of the first week. During the second and third week there is no difference between the cold and control plasma ketone concentration. The data suggest that FFA is mobilized as a metabolic substrate during cold exposure and that efficient peripheral utilization of the elevated plasma FFA concentration minimizes hyperketogenesis. ketone bodies; metabolism; nonesterified fatty acids Submitted on April 27, 1964

Responses of Captive Common Vampires to Cold and Warm Environments

When exposed to a cold environment (3°–5°C) common vampires quickly respond by increasing their food consumption and muscular activity. Both functions return promptly to normal levels when the ambient temperature is again raised. During relatively brief periods of cold exposure the animals remain normally alert and responsive, showing no evidence of induced torpor. They die, however, from within a few hours to three days when they are continuously exposed to temperatures of 3°–5°C. The great individual variation in the tolerance of cold observed among the experimental animals may indicate a capacity for physiological acclimation in captive specimens; nevertheless, the vampire's inability to withstand prolonged periods of cold exposure undoubtedly places a physiological limitation on its capacity to extend its range into more temperate latitudes. Collectively the observations suggest that the vampire bat is homeothermic. It raises its heat production by increasing metabolism and muscular activity when exposed to cold. Incidental observations upon vampires in warm environments indicate that the upper critical environmental temperature lies in the range of 27°–30°C.

Effects of oxygen inhalation on responses to cold exposure.

The effects of oxygen inhalation on shivering and thermal and metabolic responses to exposure to cold (10 C) were determined in ten healthy male subjects. The results showed that oxygen breathing reduced shivering and promoted a feeling of greater comfort. The ventilatory response to cold was diminished, and oxygen consumption was significantly lower during the later periods of the cold exposure. Carbon dioxide production was reduced and the mobilization of nitrogen during the initial periods of cold exposure was also noted. Since body temperatures and their rates of fall were not significantly altered by oxygen inhalation, a shift to more efficient metabolic heat production seems indicated. Submitted on February 6, 1961

Effects of oral glycine during cold exposure in man.

Six male human subjects were given 30 gm oral glycine. Oxygen consumption, skin and rectal temperatures, and forefinger blood flows were measured during an interval in a warm room and then during 75 minutes cold exposure (0°F). The same subjects receiving 30 gm glucose served as controls. Glycine increased heat production at rest in a warm room and also during cold exposure. The subjects when receiving glycine had a slightly higher rectal temperature and higher skin temperatures in areas other than fingers during the cold exposure period. Submitted on August 1, 1958

Effect of extreme cold exposure on adrenocortical function in the unanesthetized dog.

Unanesthetized dogs with polyethylene cannulas in the right lumboadrenal vein were subjected to environmental temperatures of –46 to –50°C for 2–28 hours and –75 to –79°C for 4–5 hours. Adrenal venous blood samples were collected prior to, and during the periods of cold exposure, and analyzed for 17-hydroxycorticosteroids. In both temperature ranges, a marked increase in adrenal steroid output occurred soon after the onset of exposure in the 10 dogs studied. In 9 of the 10 animals, this response persisted for 1–3 hours after which adrenal steroid secretion returned to control, pre-exposure levels, despite continued cold exposure. The intravenous administration of 40 iu of ACTH produced a subsequent increase in adrenal 17-hydroxycorticosteroid output. Healthy dogs exposed to temperatures of –47°C for 28 hours and –79°C for 5 hours did not become hypothermic.

Effect of the posterior pituitary hormone on the function of the thyroid gland.

1. In male albino rats, adapted to live at29.5°C. for a period of more than 8weeks, and then exposed to cold environmental temperature between10°and 15°C. for 10 days, a rise in oxygen consumption occurred. The histological picture of the thyroid indicated hyperactivity of the gland. However, change in the level of PBI was small.2. In the heat adapted rats, which were successively given vasopressin or oxytocin, there was no significant change in oxygen consumption. However, the level of PBI became lower in the case of vasopressin but not in the case of oxytocin. Histological picture indicated a slightly depressed activity of the thyroid after vasopressin and also after oxytocin.3. Rats were adapted to live at29.5°C. for the same time and then exposed to cold temperature between10°C and15°C. for10days and they were successively administered with the posterior pituitary hormone during a period of cold exposure. In the case of vasopressin the rate of rise in oxygen consumption and the level of PBI were remarkably lower than that of control ones which were exposed to cold but not given any vasopressin. Histological examination also showed an evidence of inhibitory effect on increasing of thyroid activity due to cold exposure. In the case of oxytocin these effects were hardly found.

Hematological Changes Influenced by Short and Long Exposure to Gold

SummaryMice were exposed to cold (5°C) for periods of 15 minutes and 5 days and the effect on erythrocyte number, hemoglobin concentration and blood sugar level determined. The only significant change occurred in the blood sugar level during the short period of cold exposure. Statistically this change had a P value of <.001. Possible physiological changes are discussed.

Decreased Resistance of Pyridoxine-Deficient Rats to Gold Exposure.

Immature rats were fed a purified ration containing all the known B vitamins in synthetic form and a similar diet with pyridoxine omitted. Tests were conducted in which rats fed the above diets were exposed to cold (2 ± 1.5°C) from the first day of feeding or after an experimental period of 80 days. 68.8% of the pyridoxine-deficient rats in the latter group succumbed during a 20 day period of cold exposure in contrast to a 0% mortality for animals fed a similar diet supplemented with pyridoxine hydrochloride. In the group exposed to cold from the first day of feeding mortality was 25.0% and 18.7% respectively for rats fed the pyridoxine-deficient and control ration for a period of 100 days.