Measurement of mean arterial pressure in rats by a tail-cuff method with sensitive photoelectric sensors

We evaluated a recently developed tail-cuff apparatus containing sensitive photoelectric sensors in the measurement of arterial pressure in rats. A total of 48 male Wistar rats were used in the study. The indirect mean arterial pressure (MPi) was determined from the cuff pressure when the pulse volume oscillations were maximal. To create sufficiently large pulse volume oscillations, we heated the rats for about 12 minutes at 38 degrees C prior to recording the pressure. The heating increased the mean arterial pressure by an average of 4 +/- 2 mmHg, as indicated by direct measurement of pressure. Three different sizes of cuffs were tested, with the result that the indirect measurements were nearly identical to those obtained directly when an appropriate cuff size was selected. The MPi was well correlated with the direct measurement of mean arterial pressure before (r = 0.918, p less than 0.001) and during (r = 0.903, p less than 0.001) elevation of arterial pressure via norepinephrine infusion. These results indicate that the MPi determined at maximum pulse volume oscillations coincides fairly well with the true mean arterial pressure.     

Telemetric Blood Pressure Assessment in Angiotensin II-Infused ApoE-/- Mice: 28 Day Natural History and Comparison to Tail-Cuff Measurements

Abdominal aortic aneurysm (AAA) is a disease of the aortic wall, which can progress to catastrophic rupture. Assessment of mechanical characteristics of AAA, such as aortic distensibility, may provide important insights to help identify at-risk patients and understand disease progression. While the majority of studies on this topic have focused on retrospective patient data, recent studies have used mouse models of AAA to prospectively evaluate the evolution of aortic mechanics. Quantification of aortic distensibility requires accurate measurement of arterial blood pressure, particularly pulse pressure, which is challenging to perform accurately in murine models. We hypothesized that volume/pressure tail-cuff measurements of arterial pulse pressure in anesthetized mice would have sufficient accuracy to enable calculations of aortic distensibility with minimal error. Telemetry devices and osmotic mini-pumps filled with saline or angiotensin-II were surgically implanted in male apolipoprotein-E deficient (ApoE^-/-) mice. Blood pressure in the aortic arch was measured continuously via telemetry. In addition, simultaneous blood pressure measurements with a volume/pressure tail-cuff system were performed under anesthesia at specific intervals to assess agreement between techniques. Compared to controls, mice infused with angiotensin-II had an overall statistically significant increase in systolic pressure, with no overall difference in pulse pressure; however, pulse pressure did increase significantly with time. Systolic measurements agreed well between telemetry and tail-cuff (coefficient of variation = 10%), but agreement of pulse pressure was weak (20%). In fact, group-averaged pulse pressure from telemetry was a better predictor of a subject’s pulse pressure on a given day than a simultaneous tail-cuff measurement. Furthermore, these approximations introduced acceptable errors (15.1 ± 12.8%) into the calculation of aortic distensibility. Contrary to our hypothesis, we conclude that tail-cuff measures of arterial pulse pressure have limited accuracy. Future studies of aneurysm mechanics using the ApoE^-/-/angiotensin-II model would be better in assuming pulse pressure profiles consistent with our telemetry findings instead of attempting to measure pulse pressure in individual mice.     

Absence of selective brain cooling in pyrogen-induced fever in rabbits

In 9 rabbits the effect of intravenous administration of E. coli pyrogen 0.5 microgram/kg on the reaction of selective brain cooling was studied at ambient temperatures of 20, 30 and 40 degrees C. In the freely moving animals the temperatures of the brain, carotid artery and nuchal muscles were measured with an accuracy down to 0.05 degree C and the temperatures of the ear pinna and nasal mucosa were measured accurate to 0.5 degree C. The respiratory rate was measured as well. It was found that the spontaneous febrile reaction without the component of passive hyperthermia failed to cause selective brain cooling, even if its temperature reached higher values than in case of brain temperature rise caused only by high ambient temperature. On the other hand, when the high ambient temperature caused thermal panting, pyrogen administration at an ambient temperature of 30 degrees C could reduce panting, while at an ambient temperature of 40 degrees C intense panting initiated prior to the appearance of the febrile reaction and was associated with the fever and outlasted it.     

Reversal of depressed miduterine arterial flow during hyperthermia-induced respiratory alkalosis

The influence of ambient and arterial PCO2 on miduterine arterial flow of pregnant sheep acutely exposed to hot environments was investigated. Five mixed-breed ewes between 120 and 130 days of gestation were subjected to hot environments (increasing from thermoneutral 23 to 40 degrees C), and arterial blood pH, PCO2, and PO2 were determined at 5-min intervals. Respiratory rate, heart rate, rectal temperature, blood pressure, and miduterine arterial flow were continuously monitored prior to and during elevation of ambient air temperature. When miduterine arterial flow had decreased to 50% of thermoneutral control levels, ambient air CO2 was increased to 2.5%. Elevated ambient inspired CO2 caused a reversal in arterial pH and PCO2 to near thermoneutral levels. Miduterine arterial flow increased to 77% of the control levels following the elevated ambient PCO2 period. Respiratory rate also decreased when ambient CO2 was increased but remained 136% greater than the thermoneutral control level. All other parameters remained near their heat stress (40 degrees C) level during the elevation of ambient CO2. These data indicate that heat-stress-induced depression of miduterine arterial flow is vasoactively regulated, and cause-effect related to both arterial pH and PCO2, and thermoregulatory shunting of blood to heat-dissipating surfaces.     

The structure and insulation properties of the reindeer fur

The structure of the fur of the reindeer (6 adults, 4 calves) was studied with light and scanning electron microscopy and skin and rectal temperatures were measured in 216 living animals at varying ambient temperatures (-28 to +15 degrees C) and also on excised skin samples in the laboratory (temperature range -20 to +20 degrees C, wind 0 or 10 m/sec, 5 different directions). Guard hair count and length varied according to the site of excision and were on average 2000/cm2 and 12 mm on the foreleg, 1000/cm2 and 30 mm on the abdomen and 1700/cm2 and 30 mm on the back. The corresponding counts in the calves were higher but the hairs were shorter. The rectal temperatures ranged from 38 to 40 degrees C independently of the ambient temperature. The dependence of the skin temperature on the ambient temperature was complex in living animals. The dependence was strongest in the legs. The skin temperature of the excised samples depended rather linearly on the ambient temperature. It is concluded that the reindeer can maintain its body temperature also in severe cold although the extremities show characteristics of heterothermia.     

Evaluation of miniature data loggers for body temperature measurement during sporting activities

We recorded body temperatures in four runners, two squash players and one swimmer at 1-min intervals using miniature data loggers. These single-channel loggers are small and light (25 g), and were easily carried by the athletes during their sporting activities. Wide-range loggers (-37 degrees C to +46 degrees C), which had a temperature resolution of 0.4 degrees C, were used to measure thigh skin temperature. Auditory canal temperature and rectal temperature were measured with narrow-range loggers (+34 degrees C to + 46 degrees C) which had a considerably higher resolution (0.04 degrees C). With the aid of visual analogue scales subjects reported that the thermometric equipment caused very little discomfort or impairment of exercise performance. Loggers connected to uncoated bead thermistors (used for skin and auditory canal temperatures) had a thermal time constant of 0.4 s, and that of the coated thermistors (rectal probes) was 6 s. We were able to waterproof the equipment and measure rectal temperature in a swimmer. Hot (35 degrees C) or cold (5 degrees C) ambient temperatures had an insignificant effect on the intrinsic accuracy of the data loggers, even when used without recalibration at those temperatures. We believe that miniature temperature loggers are convenient and accurate thermometers for use during sporting activities and may provide new insights into thermoregulation during exercise.     

Metabolic effects of exposure to hypoxia plus cold at rest and during exercise in humans

To determine effects on metabolic responses, subjects were exposed to four environmental conditions for 90 min at rest followed by 30 min of exercise: breathing room air with an ambient temperature of 25 degrees C (NN); breathing room air with an ambient temperature of 8 degrees C (NC); hypoxia (induced by breathing 12% O2 in N2) with a neutral temperature (HN); and hypoxia in the cold (HC). Hypoxia increased heart rate (HR), systolic blood pressure (SBP), pulmonary ventilation (VE), respiratory exchange ratio (R), blood lactate, and perceived exertion during exercise while depressing rectal temperature (Tre) and O2 uptake (VO2). Cold exposure elevated SBP, diastolic blood pressure (DBP), VE, VO2, blood glucose, and blood glycerol but decreased HR, Tre, and R. Shivering and DBP were higher and Tre was lower in HC compared with NC. HR, SBP, VE, R, and lactate tended to be higher in HC compared with NC, whereas VO2 and blood glycerol tended to be depressed. These results suggest that cold exposure during hypoxia results in an increased reliance on shivering for thermogenesis at rest whereas, during exercise, heat loss is accelerated.     

Respiratory enthalpy changes in mine rescue workers exercising under heat stress

Respiratory enthalpy change, rectal temperature, and heart rate of mine rescue workers exercising at a metabolic energy production rate of 4 met (1 met-58.15 W.m-2) in a 40 degrees C saturated environment, wearing closed-circuit breathing apparatus, were continuously measured in 10 volunteer subjects. The effects of using liquid O2 and compressed O2 apparatus were compared in each subject. Evaporative heat exchange was much greater with the liquid O2 type of apparatus, causing a significantly lower rate of rise of rectal temperature and heart rate. Convective heat exchange was negligible. Mean values for evaporative heat loss (maximum) were 61 +/- 16 (SD) W with liquid O2 and 20 +/- 18 W with compressed O2 (P less than 0.0001, 2-sided t test). Mean values for rectal temperature (rate of increase) were 0.022 +/- 0.009 (SD) degrees C.min-1 for liquid O2 and 0.036 +/- 0.015 degrees C.min-1 for compressed O2 (P less than 0.005, 2-sided paired t test). Mean values for heart rate (rate of increase) were 2.64 +/- 0.74 (SD) min-2 for liquid O2 and 3.27 +/- 0.89 min-2 for compressed O2 (P less than 0.02, 2-sided paired t test). This study quantifies, for the first time, the respiratory enthalpy change in exercising heat-stressed mine rescue workers and shows, from a physiological point of view, that the liquid O2 apparatus is clearly superior to the compressed O2 apparatus.     

Heat exchange of the rat in thermoneutral zone temperature and comparison with heat exchange in ambient temperature over and under it

With the help of thermonetry and general calorimetry body temperature and heat production in ambient temperatures 20 degrees C, 28 degrees C, 33 degrees C were recorded. The experiments showed, that at the temperature 20 degrees C the rectal temperature was changing very little. But in ambient temperature 33 degrees C the rectal temperature was 40.5 +/- 0.1 degrees C.     

Comparison of simultaneous measurement of mouse systolic arterial blood pressure by radiotelemetry and tail-cuff methods

Radiotelemetry of mouse blood pressure accurately monitors systolic pressure, diastolic pressure, heart rate, and locomotor activity but requires surgical implantation. Noninvasive measurements of indirect systolic blood pressure have long been available for larger rodents and now are being reported more frequently for mice. This study compared mouse systolic arterial blood pressure measurements using implanted radiotelemetry pressure transducer with simultaneous tail-cuff measurements in the same unanesthetized mice. The pressure range for comparison was extended by inducing experimental hypertension or by observations of circadian elevations between 3 AM and 6 AM. Both trained and untrained tail-cuff operators used both instruments. Every effort was made to follow recommended manufacturer's instructions. With the initial flow-based tail-cuff instrument, we made 671 comparisons (89 sessions) and found the slope of the linear regression to be 0.118, suggesting poor agreement. In an independent assessment, 277 comparisons (35 sessions) of radiotelemetry measurements with the pulse based tail-cuff instrument were made. The slope of the linear regression of the simultaneous measurements of systolic pressures was 0.98, suggesting agreement. Bland-Altman analysis also supported our interpretation of the linear regression. Thus although reliable systolic pressure measurements are possible with either tail-cuff or radiotelemetry techniques, in our hands some tail-cuff instruments fail to accurately detect elevated blood pressures. These data, however, do not distinguish whether this instrument-specific tail-cuff failure was due to operator or instrument inadequacies. We strongly advise investigators to obtain an independent and simultaneous validation of tail-cuff determinations of mouse blood pressure before making critical genotyping determinations.     

Blood gas analysis: effect of air bubbles in syringe and delay in estimation.

Two common sources of error in blood pH and blood gas analysis were studied. The effect of delay in estimation was studied in 10 volunteers and 40 patients. Syringes were stored at 0 degree C, (crushed ice), 4 degrees C (refrigerator) and 22 degrees C (room temperature). The pressure of oxygen (PO2) fell significantly by 20 minutes at 4 degrees C and 22 degrees C but did not change significantly at 0 degree C for up to 30 minutes. Blood pH, pressure of carbon dioxide (PCO2), and base excess did not change significantly for up to 30 minutes at 4 degrees C and 22 degrees C and up to 60 minutes at 0 degrees C. The effect of air bubbles in the syringe was studied by leaving a single bubble or froth in contact with the blood for one to five minutes in 40 patients. Po2 rose significantly after two minutes'' contact with froth and two minutes'' contact with the air bubble, and PCO2 fell significantly after three minutes'' contact with the air bubble. Size of the bubble had little effect on rates of change. Blood pH, bicarbonate, TCO2, and base excess did not change significantly after up to five minutes'' contact. For accurate estimation of PO2 and PCO2 it is necessary to avoid frothing, to expel all air bubbles within two minutes, and to inject the sample into the machine within 10 minutes or store the syringe in crushed ice. The requirements for blood pH and base excess measurement are less exacting.     

Temperature-triggered periodical thermogenic oscillations in skunk cabbage (Symplocarpus foetidus)

The natural occurrence of temperature-triggered and light-independent thermogenic oscillation in the spadix of skunk cabbage, Symplocarpus foetidus, was discovered. The identified thermogenic oscillator had an accurate periodical cycle (ca. 60 min per cycle) that apparently responded to an increase or decrease in the spadix temperature with a threshold of less than 0.9 degrees C. Neither a constant ambient air temperature nor transient changes in the ambient air temperature within 10 min (19 degrees C --> 15 degrees C --> 19 degrees C) induced the temperature oscillation in the spadix. Moreover, the periodical cycles were independent of the weight of the spadix (2.5-9.2 g) and the amplitudes of the temperature oscillations were correlated with the magnitude of the changes in the spadix temperatures. These results imply that periodical temperature oscillations in the spadix of S. foetidus possess a quantitative regulatory process that involves a temperature sensation and subsequent heat production. Based on these results, we propose a time-dependent thermogenic oscillatory model that acts as a precise thermal regulator under dynamic environmental temperature changes.     

Thermogenic responses of high-altitude adapted rats on low temperatures and low pressures

The male rats were raised in two groups, one at Mt. Yatsugatake (2,100 m above sea level, the average ambient temperature 12.5 degrees C) for 30 days, and the other at a laboratory of Matsumoto (610 m above sea level, the average temperature 20 degrees C). The steady-state oxygen consumptions (VO2) and the rectal temperatures (TR) were measured under exposure conditions of various temperatures combined with different simulated altitudes. The values of VO2 and TR for a control group at 610 m-20 degrees C were regarded as 100% and the relative changes to the control values were obtained at various temperatures in the respective low-pressure condition. When measured at a simulated altitude of 2,000 m on the 2nd day after the rats raised at Mt. Yatsugatake were translocated to Matsumoto, the values at 0 degrees C and 10 degrees C room temperatures, VO2 and TR, were still significantly increased as compared with those of rats raised at Matsumoto. On the 40th day after the translocation from Mt. Yatsugatake, however, the values turned out to exhibit no significant difference in both groups. These results indicated that the greater thermogenesis of high-altitude adapted rats had been established by combined stimuli of low temperatures and low pressures as compared with those of Matsumoto-level adapted rats, but the responses returned to the control level by deadaptation process at 40 days after the translocation.     

Measuring Blood Pressure in Mice using Volume Pressure Recording, a Tail-cuff Method

The CODA 8-Channel High Throughput Non-Invasive Blood Pressure system measures the blood pressure in up to 8 mice or rats simultaneously. The CODA tail-cuff system uses Volume Pressure Recording (VPR) to measure the blood pressure by determining the tail blood volume. A specially designed differential pressure transducer and an occlusion tail-cuff measure the total blood volume in the tail without the need to obtain the individual pulse signal. Special attention is afforded to the length of the occlusion cuff in order to derive the most accurate blood pressure readings. VPR can easily obtain readings on dark-skinned rodents, such as C57BL6 mice and is MRI compatible. The CODA system provides you with measurements of six (6) different blood pressure parameters; systolic and diastolic blood pressure, heart rate, mean blood pressure, tail blood flow, and tail blood volume. Measurements can be made on either awake or anesthetized mice or rats. The CODA system includes a controller, laptop computer, software, cuffs, animal holders, infrared warming pads, and an infrared thermometer. There are seven different holder sizes for mice as small as 8 grams to rats as large as 900 grams.Open in a separate windowClick here to view.^{(51M, flv)}     

Effect of beta-adrenergic blockade on thermoregulation during exercise

To resolve conflicting reports concerning the effects of beta-blockade (BB) on thermoregulatory reflexes during exercise, we studied six fit men during 40 min of cycle ergometer exercise at 60% maximum O2 consumption at ambient temperatures of 22 and 32 degrees C. Two hours before exercise, each subject ingested a capsule containing either 80 mg of propranolol or placebo in single-blind fashion. Heart rate at 40 min of exercise was reduced (P less than 0.01) from 125 to 103 beats min at 22 degrees C and 137 to 104 beats min at 32 degrees C, demonstrating effective BB. After 40 min of exercise, esophageal temperature (Tes) was elevated with BB (P less than 0.05) from 37.66 +/- 0.04 to 38.14 +/- 0.03 and 38.13 +/- 0.04 to 38.41 +/- 0.04 degrees C at 22 and 32 degrees C, respectively. The elevated Tes resulted from a reduced core-to-skin heat flux at both temperatures, indicated by a reduction in the slope of the forearm blood flow (FBF)-Tes relationship, and a decrease in maximal FBF. Systolic blood pressure was decreased 20 mmHg with BB (P less than 0.01), whereas diastolic blood pressure was unchanged, reducing arterial pulse pressure (PP). Because PP was decreased and cardiac filling pressure was presumably not reduced (since cardiac stroke volume was elevated), we suggest that at least a part of the relative increase in peripheral vasomotor tone during BB was the consequence of reduced sinoaortic baroreceptor stimulation.     

Estrogen replacement in middle-aged women: thermoregulatory responses to exercise in the heat.

Thermoregulatory, cardiovascular, and body fluid responses during exercise in the heat were tested in five middle-aged (48 +/- 2 yr) women before and after 14-23 days of estrogen replacement therapy (ERT). The heat and exercise challenge consisted of a 40-min rest period followed by semirecumbent cycle exercise (approximately 40% maximal O2 uptake) for 60 min. At rest, the ambient temperature was elevated from a thermoneutral (dry bulb temperature 25 degrees C; wet bulb temperature 17.5 degrees C) to a warm humid (dry bulb temperature 36 degrees C; wet bulb temperature 27.5 degrees C) environment. Esophageal (Tes) and rectal (Tre) temperatures were measured to estimate body core temperature while arm blood flow and sweating rate were measured to assess the heat loss response. Mean arterial pressure and heart rate were measured to evaluate the cardiovascular response. Blood samples were analyzed for hematocrit (Hct), hemoglobin ([Hb]), plasma 17 beta-estradiol (E2), progesterone (P4), protein, and electrolyte concentrations. Plasma [E2] was significantly (P < 0.05) elevated by ERT without affecting the plasma [P4] levels. After ERT, Tes and Tre were significantly (P < 0.05) depressed by approximately 0.5 degrees C, and the Tes threshold for the onset of arm blood flow and sweating rate was significantly (P < 0.05) lower during exercise. After ERT, heart rate during exercise was significantly lower (P < 0.05) without notable variation in mean arterial pressure. Isotonic hemodilution occurred with ERT evident by significant (P < 0.05) reductions in Hct and [Hb], whereas plasma tonicity remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)     

Metabolic rate and thermoregulation in two species of tuco-tuco, Ctenomys talarum and Ctenomys australis (Caviomorpha, Octodontidae)

1. Resting metabolic rate and body temperature in function of ambient temperature were determined for two species of Ctenomys. 2. Oxygen consumption was lowest between 25 and 30 degrees C and was 0.946 +/- 0.030 and 0.968 +/- 0.022 in Ctenomys talarum (from Mar de Cobo and Necochea, respectively). Resting metabolic rate was 0.343 +/- 0.053 at 30 C in C. australis. 3. Mean rectal temperature at thermoneutrality was 36.1 +/- 0.13 and 37.3 +/- 0.17 in C. talarum and C. australis, respectively. 4. Limited thermoregulation occurred in C. talarum down to 20 degrees C but C. australis maintained body temperature down to 10 degrees C. 5. Both species of tuco-tucos became hyperthermic at ambient temperatures above thermoneutrality.     

Oxygen consumption and body temperature of active and resting honeybees

We measured the energy turnover (oxygen consumption) of honeybees (Apis mellifera carnica), which were free to move within Warburg vessels. Oxygen consumption of active bees varied widely depending on ambient temperature and level of activity, but did not differ between foragers (>18 d) and middle-aged hive bees (7-10 d). In highly active bees, which were in an endothermic state ready for flight, it decreased almost linearly, from a maximum of 131.4 microl O(2) min(-1) at 15 degrees C ambient temperature to 81.1 microl min(-1) at 25 degrees C, and reached a minimum of 29.9 microl min(-1) at 40 degrees C. In bees with low activity, it decreased from 89.3 microl O(2) min(-1) at 15 degrees C to 47.9 microl min(-1) at 25 degrees C and 14.7 microl min(-1) at 40 degrees C. Thermographic measurements of body temperature showed that with increasing activity, the bees invested more energy to regulate the thorax temperature at increasingly higher levels (38.8-41.2 degrees C in highly active bees) and were more accurate. Resting metabolism was determined in young bees of 1-7 h age, which are not yet capable of endothermic heat production with their flight muscles. Their energy turnover increased from 0.21 microl O(2) min(-1) at 10 degrees C to 0.38 microl min(-1) at 15 degrees C, 1.12 microl min(-1) at 25 degrees C, and 3.03 microl min(-1) at 40 degrees C. At 15, 25 and 40 degrees C, this was 343, 73 and 10 times below the values of the highly active bees, respectively. The Q(10) value of the resting bees, however, was not constant but varied in a U-shaped manner with ambient temperature. It decreased from 4.24 in the temperature range 11-21 degrees C to 1.35 in the range 21-31 degrees C, and increased again to 2.49 in the range 30-40 degrees C. We conclude that attempts to describe the temperature dependence of the resting metabolism of honeybees by Q(10) values can lead to considerable errors if the measurements are performed at only two temperatures. An acceptable approximation can be derived by calculation of an interpolated Q(10) according to the exponential function (V(O(2))=0.151 x 1.0784(T(a))) (interpolated Q(10)=2.12).     

Are non-thermal factors important in the cutaneous vascular response to exercise? A proponent's view.

Direct forearm blood flow measurements showed that the threshold for vasodilation is shifted to a higher core temperature and that the slope describing the relationship between skin blood flow and core temperature is reduced during submaximum exercise in comparison with supine resting conditions. These changes in skin blood flow characteristics have been shown to be proportionately related to work load in at least one study, but not in others. With heavy exercise, indirect evidence was obtained for the elicitation of vasoconstriction after body core temperature had attained a level of 39 degrees C; this caused a dramatic rise of T core to above 40 degrees C. In other studies, such terminal vasoconstriction was not observed; the subjects stopped exercising (75 percent VO2 max), independently of its duration, when rectal temperature had reached about 39 degrees C. Such inconsistent results in regard to the importance of extrathermal control of skin blood flow may be traced to variations in the motivational and emotional state; moreover, a phenomenon described as "short-term adaptation" may be responsible for some discrepant results. In conclusion, there is evidence for the concept that blood pressure control by peripheral vasoconstriction may have, under certain circumstances, preference over the demands of temperature regulation.     

The effects of fur on the thermal regulation of mice (Mus musculus)

In order to ascertain the thermal insulation function of fur in mice, food and water intakes and rectal and skin temperatures were observed in Jcl: ICR mice and a group of the same species with their fur clipped, as well as BALB/C nu/+ and nu/nu mice. Food and water intakes increased as the ambient temperature dropped. The rectal temperature remained almost unchanged at ambient temperatures of from 18 to 30 degrees C. Skin temperatures were highest at side of the abdomen, lower at the neck, and lowest at the head. There was a tendency for skin temperatures to increase as the ambient temperature rose. The skin temperatures of mice with fur were higher than those of mice without fur. The thermal insulation of fur was 0.25, 0.14 and -0.06 clo at 18, 22, 26 and 30 degrees C in ICR mice, and 0.36, 0.01, 0.01 and -0.03 clo at 18, 22, 26 and 30 degrees C in BALB/C mice, respectively. These results confirm that heat loss from the skin at low temperatures could be prevented by the presence of fur. It also appeared that the hairless mice mutant had a lower metabolic rate than the animals with their fur clipped.