Metabolic responses of chicken embryos to graded, prolonged alterations in ambient temperature

1. Chicken embryos aged 12, 16, 18 and 20 (externally pipped) days of incubation were exposed to graded reductions (2 degrees C) in ambient temperature from 38 to 28 degrees C, exposure to each temperature lasting up to 9 hr. 2. Oxygen uptake was measured first at 38 degrees C and then in the quasi-equilibrium state at lowered temperatures. The temperature coefficient (Q10) was calculated for each egg. 3. For mild cooling (32 degrees C), the Q10 in 18-day-old embryos was about 1.5, while 12- and 16-day-old embryos had a Q10 value of about 2, indicating that a feeble homeothermic metabolic response to cooling appears in late prenatal embryos. It became more marked in externally pipped embryos and further augmented in hatchlings.     

Thermal and metabolic responsiveness of Japanese quail embryos following periodic exposure to 2,450 MHz microwaves

Two studies were performed to determine if repeated exposure of the avian egg to microwaves can alter metabolism, temperature, and growth rate of embryos. Another aim was to supplement conventional heating with microwave heating and provide an optimal temperature for growth. Japanese quail (Coturnix coturnix japonica) eggs were exposed from day 1 through 15 of incubation (8 h/day) to sham or microwave (2,450 MHz) irradiation. Microwave exposures were at two power densities, 5 or 20 mW/cm2, and at three ambient temperatures (Tas), 30.0, 33.1, or 35.4 degrees C. Specific absorption rates for unincubated and 15-day-old incubated eggs were, respectively, 0.76 and 0.66 W kg-1 mW-1 cm-2 (i.e., 3.8 and 3.3 W/kg at 5 mW/cm2 and 15.2 and 13.2 W/kg at 20 mW/cm2). Eggs were concurrently sham exposed at each of five Tas, ranging from 27.9 to 37.5 degrees C. Tests were conducted during the 16th day of incubation (i.e., 1 day post-treatment), in the absence of microwaves, to determine metabolic rate of embryos and internal and external egg temperatures at different Tas. Repeated exposures to microwaves at 5 and 20 mW/cm2 at the same Ta (30 degrees C) increased wet-embryo mass on the 16th day by an average, respectively, of 9% and 61% when compared with predicted masses for embryos exposed at the same Ta in the absence of microwave radiation. There was no reliable indication, from post-treatment tests and comparisons with control embryos of similar mass, that repeated exposure to microwave radiation resulted in abnormal physiological development. Microwave radiation can be used to increase egg temperature and embryonic growth rate at Tas below normal incubation level without altering basic metabolic and thermal characteristics of the developing bird.     

Tolerance of chick embryos to low temperatures in reference to the heart rate

Ten-day-old embryos were exposed to 28, 18 and 8 degrees C environments and their electrocardiograms (ECG) monitored. Embryos in 28 and 18 degrees C environments maintained a constant heart rate averaging 97 and 25 beats/min, respectively, followed by arrhythmias and cardiac arrest at 101 and 59 hr. Embryos in an 8 degrees C environment went into cardiac arrest after 2-4 hr, but recovered 20 hr later upon rewarming to 38 degrees C. Six to 20-day-old embryos exposed to 8 degrees C were examined for tolerance time after cardiac arrest. The younger the embryo the longer its tolerance to prolonged cardiac arrest.     

The storage of cow eggs at room temperature and at low temperatures.

The survival and development of cow eggs in the rabbit oviduct after storage at room temperature and after cooling and storage at 0-7-5 degrees C was examined. In PBS medium at room temperature 88% of Day-5 and 85% of Day-3 eggs showed normal development, but in TCM 199, 71% of Day-5 and only 49% of Day-3 eggs showed normal development. Duration of storage (1 1/2-2 hr or 6 1/2-7 1/2 hr) and cleavage stage before storage had no appreciable effect on development. Some retardation of development occurred in Day-3 eggs after 96 hr in the rabbit oviduct when compared to Day-5 eggs after 48 hr. Cooling of Day-5 and Day-6 eggs to 0-7-5 degrees C resulted in degeneration of a large proportion of eggs. Of the factors examined, storage medium (PBS or PBS+20%FCS), storage time (2 min, 24 hr) and storage temperature (0, 2, 5 or 7-5 degrees C) had little effect, but slower cooling rates tended to improve survival of eggs although the differences were not significant. More morulae (greater than 32 cells) than 8-to 24-celled eggs developed normally.     

Teratogenic effects of sinusoidal extremely low frequency electromagnetic fields on morphology of 24 hr chick embryos

To examine the potential teratogenicity of electromagnetic fields (EMF; sinusoidal and rectangular) on development of chick embryos (white leghorn), 221 freshly fertilized chicken eggs (55-65 g) were exposed during first 24 hr of postlaying incubation (38 degrees +/- 0.5 degree C) to 24 different EMFs, with 50Hz repetition rate and 8.007-10.143 mT flux density. Following exposure, the exposed fertilized chicken eggs (n = 8-10) and sham-exposed fertilized chicken eggs (n = 15) were incubated simultaneously for 8 more days and unexposed control fertilized chicken eggs (n = 20) for 9 days in absence of EMFs. The embryos were removed from egg shells and studied blind. All 24 EMF exposed-groups (inside the coil with exposure) showed an increase in the percentage of developmental anomalies compared to sham-exposed (inside the coil with no exposure) and control groups (outside the coil). Further, egg's weight was evaluated on day 9. This variable did not show significant difference between control and exposed-groups. The investigation also covered the measurement of body weight, length of crown to rump, length of tip of the beak to occipital bone, heart and liver weight. Statistical comparison between sham-exposed and control values did not show significant differences, but comparison between 8.007, 8.453 and 8.713 mT exposed-groups and control groups showed significant differences; in other exposed-groups, the changes were not significant. These results revealed that 50 Hz electromagnetic fields can induce irreversible developmental alterations in 24 hr chick embryos and confirm that its strength could be a determinant factor for the embryonic response to extremely low frequency electromagnetic fields (window effects).     

Expression of heat shock protein in broiler embryo tissues after acute cold or heat stress

This study evaluated the expression of heat shock protein 70 kD (hsp70) in broiler chicken embryos subjected to cold (Experiment I) or high incubation temperature (Experiment II). In each experiment, fertile eggs were distributed in three incubators kept at 37.8 degrees C. At day 13 (D13), D16, and D19 of incubation, the embryos were subjected to acute cold (32 degrees C) or heat (40 degrees C) for 4-6 hr. Immediately after cold or heat exposure, samples from the liver, heart, breast muscle, brain, and lungs of 40 embryos were taken per age and treatment (control or stressed embryos). A tissue pool from 10 embryos was used as 1 replication. The levels of hsp70 in each tissue sample was quantified by Western blot analysis. The data were analyzed in a 3 x 2 factorial arrangement of treatments with four replications. hsp70 was detected in all embryo tissues, and the brain contained 2- to 5-times more hsp70 protein compared to the other tissues in either cold or heat stressed embryos. hsp70 increases were observed in the heart and breast muscle of cold stressed embryos at D16 and D19, respectively. Heat stressed embryos showed an increase of hsp70 in the heart at D13 and D19, and in the lung at D19 of incubation. Younger embryos had higher hsp70 synthesis than older embryos, irrespective of the type of thermal stressor. The results indicate that the expression of hsp70 in broiler chicken embryos is affected by cold and heat distress, and is tissue- and age-dependent.     

Thermal, metabolic, and cardiovascular responses to various degrees of cold stress.

The metabolic, thermal, and cardiovascular responses of two male Caucasians to 1 2 h exposure to ambient temperature ranging between 28 degrees C and 5 degrees C were studied and related to the respective ambient temperatures. The metabolic heat production increased linearly with decreasing ambient temperature, where heat production (kcal times m- minus 2 times h- minus 1) = minus 2.79 Ta degrees C + 103.4, r = -0.97, P smaller than 0.001. During all exposures below 28 degrees C, the rate of decrease in mean skin temperature (Tsk) was found to be an exponential function dependent upon the ambient temperature (Ta) and the time of exposure. Reestablishment of Tsk steady state occurred at 90-120 min of exposure, and the time needed to attain steady state was linearly related to decreasing Ta. The net result was that a constant ratio of 1.5 of the external thermal gradient to the internal thermal gradient was obtained, and at all experimental temperatures, the whole body heat transfer coefficient remained constant. Cardiac output was inversely related to decreasing Ta, where cardiac output (Q) = minus 0.25 Ta degrees C + 14.0, r = minus 0.92, P smaller than 0.01. However, the primary reason for the increased Q, the stroke output, was also described as a third-order polynomial, although the increasing stroke volume throughout the Ta range (28-5 degrees C) was linearly related to decreasing ambients. The non-linear response of this parameter which occurred at 20 degrees C larger than or equal to Ta larger than or equal to 10 degrees C suggested that the organism's cardiac output response was an integration of the depressed heart rate response and the increasing stroke output at these temperatures.     

Thermoregulatory responses of the immature rat following repeated postnatal exposures to 2,450-MHz microwaves

This study was designed to determine the changes that occur in the thermoregulatory ability of the immature rat repeatedly exposed to low-level microwave radiation. Beginning at 6-7 days of age, previously untreated rats were exposed to 2,450-MHz continuous-wave microwaves at a power density of 5 mW/cm2 for 10 days (4 h/day). Microwave and sham (control) exposures were conducted at ambient temperatures (Ta) which represent different levels of cold stress for the immature rat (ie, "exposure" Ta = 20 and 30 degrees C). Physiological tests were conducted at 5-6 and 16-17 days of age, in the absence of microwaves, to determine pre- and postexposure responses, respectively. Measurements of metabolic rate, colonic temperature, and tail skin temperature were made at "test" Ta = 25.0, 30.0, 32.5, and 35.0 degrees C. Mean growth rates were lower for rats exposed to Ta = 20 degrees C than for those exposed to Ta = 30 degrees C, but microwave exposure exerted no effect at either exposure Ta. Metabolic rates and body temperatures of all exposure groups were similar to values for untreated animals at test Ta of 32.5 degrees C and 35.0 degrees C. Colonic temperatures of rats repeatedly exposed to sham or microwave conditions at exposure Ta = 20 degrees C or to sham conditions at exposure Ta = 30 degrees C were approximately 1 degrees C below the level for untreated animals at test Ta of 25.0 degrees C and 30.0 degrees C. However, when the exposure Ta was warmer, rats exhibited a higher colonic temperature at these cold test Ta, indicating that the effectiveness of low-level microwave treatment to alter thermoregulatory responses depends on the magnitude of the cold stress.     

Susceptibility of Lasioderma serricorne (Coleoptera: Anobiidae) life stages to elevated temperatures used during structural heat treatments

Heat treatment of food-processing facilities involves using elevated temperatures (50-60 degrees C for 24-36 h) for management of stored-product insects. Heat treatment is a viable alternative to the fumigant methyl bromide, which is phased out in the United States as of 2005 because of its adverse effects on the stratospheric ozone. Very little is known about responses of the cigarette beetle, Lasioderma serricorne (F.) (Coleoptera: Anobiidae), a pest associated with food-processing facilities, to elevated temperatures. Responses of L. serricorne life stages to elevated temperatures were evaluated to identify the most heat-tolerant stage. Exposure of eggs, young larvae, old larvae, and adults during heat treatment of a food-processing facility did not clearly show a life stage to be heat tolerant. In the laboratory, exposure of eggs, young larvae, old larvae, pupae, and adults at fixed times to 46, 50, and 54 degrees C and 22% RH indicated eggs to be the most heat-tolerant stage. Time-mortality responses at each of these three temperatures showed that the time for 99% mortality (LT99) based on egg hatchability and egg-to-adult emergence was not significantly different from one another at each temperature. Egg hatchability alone can be used to determine susceptibility to elevated temperatures between 46 and 54 degrees C. The LT99 based on egg hatchability and egg-to-adult emergence at 46 degrees C was 605 and 598 min, respectively, and it decreased to 190 and 166 min at 50 degrees C and 39 and 38 min at 54 degrees C. An exponential decay equation best described LT99 as a function of temperature for pooled data based on egg hatchability and egg-to-adult emergence. Our results suggest that during structural heat treatments eggs should be used in bioassays for gauging heat treatment effectiveness, because treatments aimed at controlling eggs should be able to control all other L. serricorne life stages.     

Effect of high and low temperatures on the drugstore beetle (Coleoptera: Anobiidae)

The drugstore beetle, Stegobium paniceum (L.) (Coleoptera: Anobiidae), is a pest of stored medicinal and aromatic plants. Generally, mortality of each stage increased with an increase of temperature and exposure time. Heat tolerance for different stages from highest to lowest was young larvae, old larvae, eggs, adult, and pupae. The mortality after 7 h at 42 degrees C for young larvae, old larvae, eggs, adults, and pupae, respectively, was 16 +/- 5, 31 +/- 6, 48 +/- 3, 63 +/- 8, and 86 +/- 2% (mean +/- SEM). Similar trends for stage specific mortality were seen with the lethal time for 90% mortality (LT90) at 42 degrees C; 773, 144, 12, and 11 h for old larvae, eggs, adults, and pupa respectively. Mortality was too low with young larvae to estimate LT90. The LT90 for young larvae at 42, 45, 50, 55, and 60 degrees C was 25, 20, 3.9, 0.18, and 0.08 h, respectively. The cold tolerance of different stages at 0 degree C from highest to lowest was adults, old larvae, young larvae, pupae, and eggs. The LT90 at 0 degrees C was 298, 153, 151, 89, and 53 h, respectively. The LT90 for adults at 5, -5, -10, and -15 degrees C was 792, 58, 2, and 0.8 h, respectively. The supercooling point of adults was -15.2 +/- 2 degrees C; young larvae, -9.0 +/- 0.8 degrees C; old larvae, -6.5 +/- 0.5 degrees C; and pupae, -4.0 +/- 1.4 degrees C. Heat treatments that control young larvae should control all other stages of S. paniceum. Cold treatments that control adults should control all other stages of S. paniceum. Dried plants stored at 5 degrees C for 45 d or 42 degrees C for 30 h and then kept below 18 degrees C throughout the rest of the year, should remain pest-free without any chemical control.     

Development of calcium reabsorption by the allantoic epithelium in chick embryos grown in shell-less culture

The allantoic sac of the chick embryo functions as a primitive urinary bladder, storing and modifying the excretory fluid produced by the embryo. We have used chick embryos grown in shell-less culture to study the in situ handling of Ca2+ by the allantoic epithelium. Between Days 8 and 13 of incubation (38 degrees C, 5% CO2), the [Ca2+] of the allantoic sac fluid declines from about 1.5 mM to less than 0.3 mM, with most of this Ca2+ reabsorption occurring between Days 10 and 11. In 13-day-old embryos, the allantoic epithelium reabsorbs within 24 hr 85-92% of 45Ca2+ injected into the allantoic sac, while in 9-day-old embryos 45Ca2+ reabsorption is less than 40% by 24 hr. This is evidence for the developmental onset of a Ca2+ reabsorption process in the allantoic epithelium. The allantoic fluid Ca2+ is reabsorbed into the embryo's blood in which the serum [Ca2+] is about 1.5 mM. Also, electrical potential profiles reveal that the serosal (mesenchymal) side of the allantoic epithelium is 15-30 mV positive compared to the mucosal (luminal) side. Thus, by electrochemical criteria this reabsorption process appears to be active.     

Two-step freezing of two-cell rabbit embryos after partial dehydration at room temperature

The effect of rapid freezing and thawing on the survival of 2-cell rabbit embryos was examined. When embryos in 2.2 M-propanediol were directly plunged from room temperature to liquid nitrogen some of them survived after thawing (8%) but only if they had been pretreated by exposure to an impermeable solute, sucrose, that makes the blastomeres shrink osmotically before cooling. High survival (77-88%) in vitro was obtained when pretreated embryos were first held at -30 degrees C for 30-240 min before immersion into liquid nitrogen. Transfer of such frozen-thawed embryos gave a survival rate to live young similar to that obtained with controls (26% and 32% respectively). DMSO was less effective than propanediol; only 2 out of 38 sucrose-pretreated frozen-thawed embryos developed in vitro. The present work shows that a combination of partial dehydration of blastomeres at room temperature with their permeation by a cryoprotective agent offers a simple method for successful rapid freezing and thawing of rabbit embryos.     

Induced thermotolerance in bovine two-cell embryos and the role of heat shock protein 70 in embryonic development

Induced thermotolerance is a phenomenon whereby exposure to a mild heat shock can induce heat shock proteins (HSP) and other cellular changes to make cells more resistant to a subsequent, more severe heat shock. Given that the 2-cell bovine embryo is very sensitive to heat shock, but can also produce HSP70 in response to elevated temperature, experiments were conducted to test whether 2-cell embryos could be made to undergo induced thermotolerance. Another objective was to test the role of the heat-inducible form of heat shock protein 70 (HSP70i) in development and sensitivity of bovine embryos to heat shock. To test for induced thermotolerance, 2-cell bovine embryos were first exposed to a mild heat shock (40 degrees C for 1 hr, or 41 degrees C or 42 degrees C for 80 min), allowed to recover at 38.5 degrees C and 5% (v/v) CO2 for 2 hr, and then exposed to a severe heat shock (41 degrees C for 4.5, 6, or 12 hr). Regardless of the conditions, previous exposure to mild heat shock did not reduce the deleterious effect of heat shock on development of embryos to the blastocyst stage. The role of HSP70i in embryonic development was tested in two experiments by culturing embryos with a monoclonal antibody to the inducible form of HSP70. At both 38.5 degrees C and 41 degrees C, the proportion of 2-cell embryos that developed to blastocyst was reduced (P < 0.05) by addition of anti-HSP70i to the culture medium. In contrast, sensitivity to heat shock was not generally increased by addition of antibody. In conclusion, bovine 2-cell embryos appear incapable of induced thermotolerance. Lack of capacity for induced thermotolerance could explain in part the increased sensitivity of 2-cell embryos to heat shock as compared to embryos at later stages of development. Results also implicate a role for HSP70i in normal development of bovine embryos.     

Core temperature is regulated, although at a lower temperature, in rats exposed to hypergravic fields

1. In rats acclimated to 23 degrees C (RT rats) or 5 degrees C (CA rats), core temperature (Tc), tail temperature (Tt) and oxygen consumption (VO2) were measured during exposure to a hypergravic field. 2. Rats were exposed for 5.5 h to a 3 g field while ambient temperature (Ta) was varied. For the first 2 h, Ta was 25 degrees C; then Ta was raised to 34 degrees C for 1.5 h. During this period of warm exposure, Tc increased 4 degrees C in both RT and CA rats. Finally, Ta was returned to 25 degrees C for 2 h, and Tc decreased toward the levels measured prior to warm exposure. 3. In a second experiment at 3 g, RT and CA rats were exposed to cold (12 degrees C) after two hours at 25 degrees C. During the one hour cold exposure, Tc fell 1.5 degrees C in RT and 0.5 degree C in CA rats. After cold exposure, when ambient temperature was again 25 degrees C, Tc of RT and CA rats returned toward the levels measured prior to the thermal disturbance. 4. Rats appear to regulate their temperature, albeit at a lower level, in a 3 g field.     

Characterization of intracellular ice formation in Drosophila melanogaster embryos

Cryomicroscopy and differential scanning calorimetry (DSC) were used to characterize the incidence of intracellular ice formation (IIF) in 12- to 13-hr-old embryos of Drosophila melanogaster (Oregon-R strain P2) as influenced by the state of the eggcase (untreated, dechorionated, or permeabilized), the composition of the suspending medium (with and without cryoprotectants), and the cooling rate. Untreated eggs underwent IIF over a very narrow temperature range when cooled at 4 or 16 degrees C/min with a median temperature of intracellular ice formation (TIIF50) of -28 degrees C. The freezable water volume of untreated eggs was approximately 5.4 nl as determined by DSC. IIF in dechorionated eggs occurred over a much broader temperature range (-13 to -31 degrees C), but the incidence of IIF increased sharply below -24 degrees C, and the cumulative incidence of IIF at -24 degrees C decreased with cooling rate. In permeabilized eggs without cryoprotectants (CPAs), IIF occurred at much warmer temperatures and over a much wider temperature range than in untreated eggs, and the TIIF50 was cooling rate dependent. At low cooling rates (1 to 2 degrees C/min), TIIF50 increased with cooling rate; at intermediate cooling rates (2 to 16 degrees C/min), TIIF50 decreased with cooling rate. The total incidence of IIF in permeabilized eggs was 54% at 1 degree C/min, and volumetric contraction almost always occurred during cooling. Decreasing the cooling rate to 0.5 degree C/min reduced the incidence of IIF to 43%. At a cooling rate of 4 degrees C/min, ethylene glycol reduced the TIIF50 by about 12 degrees C for each unit increase in molarity of CPA (up to 2.0 M) in the suspending medium. The TIIF50 was cooling rate dependent when embryos were preequilibrated with 1.0 M propylene glycol or ethylene glycol, but was not so in 1.0 M DMSO. For embryos equilibrated in 1.5 M ethylene glycol and then held at -5 degrees C for 1 min before further cooling at 1 degree C/min, the incidence of IIF was decreased to 31%. Increasing the duration of the isothermal hold to 10 min reduced the incidence of IIF to 22% and reduced the volume of freezable water in embryos when intracellular ice formation occurred. If the isothermal hold temperature was -7.5 or -10 degrees C, a 10- to 30-min holding time was required to achieve a comparable reduction in the incidence of IIF.     

Factors affecting survival of mouse blastocysts vitrified by a mixture of ethylene glycol and dimethyl sulfoxide

The present study was conducted to determine suitable conditions for mouse blastocysts vitrified by a solution containing 25 % v/v (4.5M) ethylene glycol and 25% v/v (3.4M) dimethyl sulfoxide (VSi). In Experiment 1, blastocysts were exposed to 50% diluted VSi (50% VSi) for 10 minutes then to VSi for 0.5 minutes at room temperature (22 approximately 24 degrees C) or at 4 degrees C, followed by vitrification. The survival rates of these embryos exposed at each temperature were not significantly different. In Experiment 2, embryos were exposed directly to VSi for various time periods at room temperature and diluted in mPBS with 0.5 M sucrose without vitrification. The viability of embryos decreased after more than a 3 minute exposure. When the embryos were exposed to VSi for 0.5, 1, 1.5 and 2 minutes followed by vitrification, the survival rates were 78, 80, 76 and 50%, respectively. In Experiment 3, embryos were vitrified after exposure to 50% VSi for various time periods and then to VSi for 0.5 minutes at room temperature. One minute exposure to 50% VSi resulted in the highest survival rate. In Experiment 4 and 5, the cooling rate (from approximately 70 to approximately 2500 degrees C/minute), sucrose concentration (0, 0.5 and 1 M) of dilution solution, and dilution time (1 or 5 minutes) did not affect the viability of the vitrified embryos. Following exposure to 50% VSi for 1 minute and to VSi for 0.5 minutes at room temperature, embryos were cooled 1) at approximately 2500 degrees C/minute and diluted in 0.5 M sucrose in mPBS after warming or 2) at approximately 200 degrees C/minute and diluted in mPBS. In vivo development rates after the transfer to recipients were 38 and 42%, respectively. These values were similar to that of fresh control embryos.     

Survival of 4-cell mouse embryos derived from in vitro fertilization after ultrarapid freezing and thawing

Four-cell mouse embryos obtained by fertilization in vitro were frozen ultrarapidly, immediately after one-step exposure to a highly concentrated solution (modified VS1) at room temperature, and later thawed in a 37 degrees C waterbath. The proportion of morphologically normal embryos on thawing was 95.7% (198/207), and 83.8% (166/198) of these embryos developed to morulas and early blastocysts after 24 hr in culture. All frozen-thawed embryos that developed to morulas and early blastocysts were transferred to the uterine horns of recipients on day 3 of pseudopregnancy and 47.0% (78/166) of transferred embryos developed to normal young.     

Effects of hypoxia and cold acclimation on thermoregulation in the rat.

The effects of hypoxia (inspired O2 fraction = 0.12) on thermoregulation and on the different sources of thermogenesis were studied in rats before and after periods of 1-4 wk of cold acclimation. Measurements of metabolic rate (VO2) and body temperature (Tb) were made at 5-min intervals, and shivering activity was recorded continuously in groups of rats subjected to three protocols. In protocol 1, rats were exposed to normoxia to an ambient temperature (Ta) of 5 degrees C for 2 h. In protocol 2, at Ta of 5 degrees C, rats were exposed for 30 min to normoxia, then for 45 min to hypoxia, and finally for 30 min to normoxia. In protocol 3, in the non-cold-acclimated (NCA) rats, Ta was decreased from 30 to 5 degrees C in steps of 5 degrees C and of 30-min duration while in cold-acclimated (CA) rats at 5 degrees C for 4-wk, Ta was increased from 5 to 30 degrees C in steps of 5 degrees C and of 30-min duration. Recordings were made in normoxia and in hypoxia on different days in the same animals. The results showed that 1) in NCA rats, cold exposure in normoxia induced increases in VO2 and shivering that were proportional to the decrease in Ta; 2) in CA rats in normoxia, for a given Ta, VO2 and Tb were higher than in NCA rats, whereas shivering was generally lower; and 3) in both NCA and CA rats, hypoxia induced a transient decrease in shivering and a sustained decrease in nonshivering thermogenesis associated with a marked decrease in Tb that was about the same in NCA and CA rats. We speculate that hypoxia acts on Tb control to produce a general inhibition of thermogenesis. Nonshivering thermogenesis is markedly sensitive to hypoxia, especially demonstrable in CA rats; a recovery or even an increase in shivering can compensate for the decrease in nonshivering thermogenesis.     

Hyperthermia in radiofrequency-exposed rhesus monkeys: a comparison of frequency and orientation effects

To compare the effects of exposure to a near-resonant frequency of microwaves at two orientations with a higher frequency exposure, five rhesus monkeys were exposed for 4 hr to 225 MHz, electric field oriented parallel to the long axis of the body (225 MHz-E), and to 225 MHz, magnetic field orientation (225 MHz-H), or to 1290 MHz, electric field orientation. On a separate occasion, the monkeys were exposed at night to 225 MHz-E. Exposures were conducted with the animal chair restrained in an anechoic chamber with rectal temperature continuously monitored. Blood samples were taken hourly during the 225-MHz-E exposures for cortisol analysis. The power densities used were 0, 1.2, 2.5, 5.0, 7.5, 10.0, and 15.0 mW/cm2 for 225 MHz-E (day), 0 and 5 mW/cm2 (225 MHz-E night and 225 MHz-H), and 0, 20, 28, and 38 mW/cm2 (1290 MHz). The monkeys were unable to tolerate exposure at power densities equal to or greater than 7.5 mW/cm2 (5.1 W/kg) at 225 MHz-E for longer than 90 min. The criterion for tolerance was that the rectal temperature would not exceed 41.5 degrees C. Average rectal temperature increases for day exposure to 225 MHz-E were 0.4 and 1.7 degrees C for 4-hr exposures to 2.5 and 5.0 mW/cm2 (1.7 and 3.4 W/kg). No changes in circulating cortisol levels occurred during any exposures to 5 mW/cm2 or less. Night exposures to 5 mW/cm2 (3.4 W/kg) at 225 MHz-E raised mean rectal temperature 2.1 degrees C. Exposure to 5 mW/cm2 (1.2 W/kg) at 225 MHz-H for 4 hr resulted in a 0.2 degree rise in mean rectal temperature. For 4 hr of 1290-MHz exposure to 20, 28, or 38 mW/cm2 (2.9, 4.0, and 5.4 W/kg), the mean body temperature increases were 0.4, 0.7, and 1.3 degrees C, respectively. The degree of hyperthermia caused by radiofrequency (rf) exposure was shown to be frequency and orientation dependent for equivalent power densities of exposure.