CHANGES IN THE OXYGEN CONSUMPTION OF NEW-BORN GUINEA-PIGS AND RABBITS ON EXPOSURE TO COLD

Presence of mother prompts dissociation of sickness behavior, fever, and hypothalamic gene expression in lipopolysaccharide-injected guinea pig pups

During infection, sickness behaviors, such as a hunched stance with piloerection, can facilitate host resistance by supporting the generation and maintenance of fever. Fever, in turn, is mediated by hypothalamic neuroimmune signaling. Sickness behaviors, however, can also be influenced by social stimuli. In this study, guinea pig pups were injected with lipopolysaccharide to simulate a bacterial infection and then exposed to a novel, threatening environment while either with their mother or alone. We found that the presence of the mother suppressed sickness behavior, but enhanced fever, and had no measureable effect on gene expression of hypothalamic mediators of fever. This 3-way dissociation induced by the mother's presence is interpreted in terms of the differential adaptive consequences of behavioral and febrile responses for pups in this situation. The results contribute to a growing literature linking immunological and social processes.

The Development of Endothermy during Pouch Life in the Eastern Barred Bandicoot (Perameles gunnii), a Marsupial

Marsupials are born ectothermic and gradually become endothermic during pouch occupancy. In order to study the timing of this transition, we measured the metabolic rates of eight pouch-young eastern barred bandicoots (Perameles gunnii) at 25 degrees C (the thermoneutral zone of adults), at 35 degrees C (pouch temperature), and after injection with norepinephrine. From 5 to 7 wk of age, oxygen consumption (VO(2)) was higher at 35 degrees C than at 25 degrees C. At 8 wk, VO(2) was significantly higher at 25 degrees C than at 35 degrees C. Norepinephrine administration at 5 and 6 wk had no effect on metabolic rate, but at 8 wk, near pouch vacation, it resulted in a significant increase in metabolic rate. Our results indicate that signs of thermoregulation for P. gunnii begin at 7 wk, and at 8 wk the species is endothermic, that is, able to increase heat production in response to both cold and norepinephrine. The appearance of fur, first seen at the age of 6 wk and fully developed at 8 wk, coincides with the onset of endothermy.

Autonomic and behavioral thermoregulation in guinea pigs during postnatal maturation

Serial experiments were carried out on seven chronically instrumented Hartley-strain guinea pigs at 1, 3, and 5 wk of age to define their autonomic and behavioral thermoregulatory profiles and to test the hypothesis that they have the mechanisms in place shortly after birth that allow them to optimize their energy expenditure for thermoregulation by selecting a thermal environment that requires the lowest metabolic oxygen requirements. Each animal was studied in both a thermocline to determine selected ambient temperature and in a metabolic chamber to determine the thermoregulatory response to forced changes in ambient temperature. In the thermocline, the guinea pigs at all postnatal ages selected an ambient temperature that placed core temperature, oxygen consumption, thermal conductance, heart rate, and respiratory rate at levels comparable to those observed at ambient temperatures in which minimal oxygen consumption occurred in the metabolic chamber. Thus our experiments provide evidence that guinea pigs have the neurophysiological mechanisms in place shortly after birth that allow them to optimize their energy expenditure for thermoregulation by selecting a thermal environment that corresponds to the lowest metabolic oxygen requirements.

Thermoregulation in sick foals aged less than one week

Metabolic rate, rectal temperature Tr and respiratory quotient (RQ) were determined in 16 sick foals, aged 0-182 h. The foals were categorized into three groups: premature, dysmature or those suffering from neonatal maladjustment syndrome. The mean metabolic rate of the premature foals was 71 watts per unit area of body surface (W m(-2)), significantly lower than that of the other two groups. The overall mean metabolic rate for the sick foals was 82 W m(-2), about 25% below that of healthy foals of similar age. Air temperature (Ta) was 9.5-26.3 degrees C, and several foals shivered despite the provision of additional 'warmth' and insulation. Values of Tr were below 38 degrees C until after 4 h postpartum. Thereafter, Tr averaged 38.1 degrees C but fluctuated widely. The RQ (mean value 0.83) was not correlated with Ta. The lower critical temperature for the sick foals was estimated at 24 degrees C, on average. Methods to prevent excessive heat loss from sick foals are suggested.

Development of temperature regulation in the common white-toothed shrew, Crocidura russula

1. Body temperature and oxygen consumption were measured during the first month of postnatal life in two litters of Crocidura russula at four different ambient temperatures. 2. Body temperature in the nest varies from 30.5-35.0 degrees C during the first 10 days; afterwards it becomes more constant (35.5-37.0 degrees C). 3. First homoiothermic reactions occur on the 2nd day of life and become effective on the 4th day. 4. In the case of undernourished shrews, torpor is already developed on the 2nd day. 5. After the 7th day torpor is the obligatory reaction in cooling experiments. 6. This discontinuous development of temperature regulation is interpreted as typical for shrews capable of torpor.

Changes in body temperature after administration of acetylcholine, histamine, morphine, prostaglandins and related agents: II

This survey continues a second series of compilations of data regarding changes in body temperature induced by drugs and related agents. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on the presence of special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent. Most of the papers were published since 1979, but data from many earlier papers are also tabulated.

Uptakes and uses of oxygen, from gametes to maturity: an overview

How do rates of oxygen uptakes per unit of body weight change with age in mammals? Marked increases occur, starting on the third day after fertilization; small increases occur just after birth. At birth the factor of body size of the species has a small influence. In the old adult the diminished uptake per unit weight resembles that of the newly fertilized zygote. Special roles of RNA and of mitochondria determine the uses to which energy is put. Anaerobic energy is and can be employed temporarily in embryonic stages. Sensitivities to energy demands are revealed in effects of hypoxia, hyperoxia, low temperatures and norepinephrine. Uses of energy for biosyntheses and active transports change during ontogeny; and differ among the tissues. Strategies of development, and their sequences, appear to supply adequate oxygen throughout prenatal stages.

Changes in body temperature after administration of antipyretics, LSD, delta 9-THC, CNS depressants and stimulants, hormones, inorganic ions, gases, 2,4-DNP and miscellaneous agents

This survey concludes a series of complications of data from the literature, primarily published since 1965, on thermoregulatory effects of antipyretics in afebrile as well as in febrile subjects, LSD and other hallucinogens, cannabinoids, general CNS depressants, CNS stimulants including xanthines, hormones, inorganic ions, gases and fumes, 2,4-dinitrophenol and miscellaneous agents including capsaicin, cardiac glycosides, chemotherapeutic agents, cinchona alkaloids, cyclic nucleotides, cycloheximide, 2-deoxy-D-glucose, dimethylsulfoxide, insecticides, local anesthetics, poly I:poly C, spermidine and spermine, sugars, toxins and transport inhibitors. The information listed includes the species used, route of administration and dose of drug, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary agents.

Hypothalamic sensitivity to leukocytic pyrogen of adult and new-born guinea-pigs

1. Experiments were conducted to localize the hypothalamic site of action of microinjected leucocytic pyrogen and to compare the pyrogenic sensitivity of this locus in adult and new-born guinea-pigs.2. To identify the site reactive to leucocytic pyrogen, bilateral (0.8-1.0 mm from the mid line) injections of 1 microliter were made into conscious adult guinea-pigs via cannulas stereotaxically palced at 0.5 mm intervals and varying depths from the olfactory tegmentum to the mammillary bodies. Injections into the preoptic area produced sharp monophasic fevers with short latencies, whereas injections into circumjacent sites evoked smaller fevers with longer latencies. 3. To assess the ontogeny of the pyrogenic sensitivity of this locus, the febrile response to 1.00, 0.50, and 0.25 microliter leucocytic pyrogen injected bilaterally was compared to 0 to 5-, 6 to 12-, and 13 to 16-day old and in adult guinea-pigs. The minimum pyrogenic dose in both new-born and adult guinea-pigs was 0.25 microliter, but the 0 to 5-day old animals which responded with a fever to this dose were few in number and large in weight; 'small-for age' neonates became hypothermic. 4. The number of febrile animals increased with age; it also could be increased by increasing the dose of leucocytic pyrogen at any age. 5. These results suggest that febrile responsiveness may depend on the stage of development of, presumably, the pyrogen-receptive mechanism. They further imply that the preoptic sites where leucocytic pyrogen acts and thermoafferents are integrated may not be the same, since thermoregulatory capability is fully competent from birth.

Effects of alpha- and beta-adrenergic blockers on the actions of noradrenaline on body temperature in the newborn guinea-pig

The effect of NA injected into the lateral cerebral ventricle on Tc was blocked by alpha-adrenergic receptor blockers, but not by beta-receptor blockers, whereas the effect of systemically administered NA was blocked by i.p. administered beta-receptor blockers, but not by alpha-blockers.

Experimental studies on the pathophysiological responses of the newborn to injury

Experimental studies are reviewed which show that there are significant differences with age in both the local and general responses to injury. The results seem to confirm the belief in the striking ability of the newborn to withstand injury and suggest that one important aspect of this resistance is an increased ability to compensate circulatory hypovolaemia.

Regional distribution of cardiac output in young lambs: effect of cold exposure and treatment with catecholamines

1. Lambs less than 3 days old, exposed to thermoneutral or intensely cold conditions in a respiration chamber, were infused with adrenaline or noradrenaline, 1 or 10 mug/kg.min; and the effects on oxygen consumption, cardiac output and its distribution to skin, skeletal and cardiac muscle, liver, spleen, kidney, gut, brown adipose tissue and brain were determined. Cardiac output was estimated by the Fick and dye dilution methods and the distribution of cardiac output by Sapirstein's method of fractional distribution of indicators.2. Under thermoneutral conditions, metabolic rate was stimulated by both doses of noradrenaline and by the low, but not the high dose of adrenaline. Under cold conditions, the low dose of catecholamines had little effect on the already elevated metabolic rate, but the high doses depressed the metabolic response to cold.3. The low dose of adrenaline increased cardiac output under thermoneutral conditions whereas the high dose decreased cardiac output; the effects of noradrenaline were less marked, in contrast to reported effects in new-born rabbits. The low doses of catecholamine given under cold conditions had little effect on the already elevated cardiac output, but the high doses, particularly of adrenaline, decreased cardiac output.4. Blood flow through the skin of the extremities was markedly reduced by cold exposure, while flow through the peri-renal fat was doubled, flow through the skeletal muscle was quadrupled and flow through the cardiac muscle was trebled. These increases, particularly in skeletal muscle, were due to increased cardiac output and to vasodilation, as indicated by the reduced ratio of blood pressure to blood flow. Results are contrasted with published reports that blood flow through brown fat in new-born rabbits was greatly increased by cold, but muscle flow was scarcely altered.5. In almost all organs examined the high doses of adrenaline infused in either environment markedly reduced blood flow, presumably by generalized vasoconstriction. Changes due to noradrenaline were small under thermoneutral conditions and flow through brown fat was increased by only 60% during infusion of 10 mug/kg.min. Much greater increases have been reported in new-born rabbits. Under cold conditions the high doses of noradrenaline tended to decrease flow in most organs including brown fat and muscle.6. The results provide likely explanations for published reports that adrenaline failed to stimulate non-shivering thermogenesis or suppressed the mobilization of metabolites and the metabolic response to cold.

The redistribution of cardiac output on cold exposure in new-born rabbits

1. In anaesthetized new-born rabbits isotope-labelled microspheres were injected into the left ventricle to investigate the distribution of cardiac output.2. On cold exposure the proportion of radioactivity (and hence of cardiac output) distributed to brown adipose tissue rose from 6 to 19%. Similar results were obtained in ten rabbits in which the distribution of microspheres labelled with two different isotopes was examined both in a neutral thermal and cold environment.3. The perirenal, inguinal, pectoral and axillary adipose tissue deposits showed a trivial increase in the proportion of cardiac output (from 1.2 to 1.9%) on cold exposure as compared with the cervical and interscapular deposits.4. The small intestine of new-born rabbits received 24% of the cardiac output while renal flow was only 8%. There were large changes in the proportions of body weight and in the distribution of cardiac output with age from 1 to 6 days from birth.5. The results support the contention that brown adipose tissue is the principal site of additional thermogenesis in anaesthetized new-born rabbits exposed to cold.

The relation between environmental temperature and oxygen consumption in the new-born baby

1. Oxygen consumption (V(O2)) has been measured serially in sixty-eight infants during the first 10-35 days of life, when naked in a Perspex metabolic chamber, by recording the changes in circulating gas volume. Air speed in the chamber was 4-5 cm/sec, and absolute humidity approximately 18 mm Hg.2. When environmental temperature (T(E)) was 35-38 degrees C minimal V(O2) rose from 5 to 7 ml.O(2)/kg.min during the first 2 days of life in infants weighing over 2.5 kg, and more slowly in the first 7-10 days in infants under 2 kg at birth.3. Physical activity and V(O2) both increased when T(E) fell below 33 degrees C: the increase appeared to be linearly and inversely related to T(E), but the rise in heat production was seldom enough to prevent a fall in rectal temperature. In infants over 2.5 kg at birth the mean increase amounted to 0.56 ml.O(2)/kg.min for each 1 degrees C fall in T(E) when 4-12 hours old, and 1.27 ml.O(2)/kg.min when between 4 and 20 days old. In infants weighing 1-2 kg at birth the mean increase was similar in the first 12 hr, but the coefficient rose more gradually with age.4. The maximum V(O2) in infants over 2.5 kg at birth and over 2 days old was about 2(1/2) times the minimum V(O2); the maximum was rather lower in most infants of low birth weight.5. In seven infants who were motionless and apparently asleep after sedation with chloral hydrate, the increase in V(O2) at low T(E) was reduced but still significant.6. It is concluded that the new-born baby responds to a cool environment with a considerable immediate increase in heat production; visible muscular activity appears to account for only part of this increase.

Shivering and non-shivering therogenesis during summit metabolism in young lambs

1. Summit metabolism of lambs declined steadily from about 3.5 l. O(2)/kg.hr during the first day of life, to about 2.0 l. O(2)/kg.hr at 2 months of age.2. The contributions of shivering and non-shivering thermogenesis to these changes were estimated by three independent methods; non-shivering thermogenesis was stimulated by catecholamines in a thermoneutral environment, shivering was suppressed by curariform drugs during summit metabolism, and an attempt was made to suppress non-shivering thermogenesis during summit metabolism by use of the sympatholytic drugs phentolamine and propranolol. Drugs were given by intravenous infusion during measurement of oxygen consumption in a closed circuit respiration chamber.3. ;Resting' metabolic rate of lambs during the first day of life was increased two to three-fold, from 1 l. O(2)/kg.hr, by either adrenaline or noradrenaline infused at 1-10 mug/kg.min. The increase declined with increasing age of lamb and was virtually absent by 3 weeks. The response to catecholamines appeared maximal at the dose levels used.4. Muscular paralysis induced by suxamethonium or gallamine reduced summit metabolism by about 2 l. O(2)/kg.hr in all lambs examined within the first 2 months of life. The residual metabolic rate, and the metabolic response to catecholamines under thermoneutral conditions, declined with age in the same manner, and their magnitudes were similar.5. Summit metabolism in lambs aged up to 2 months was depressed to varying degrees by the sympathetic inhibitors phentolamine, propranolol and hexamethonium. The depression with propranolol was greater, and the decline with age clearer, than with phentolamine. Hexamethonium and phentolamine depressed blood pressure, propranolol decreased heart rate and phentolamine and propranolol each suppressed shivering in some experiments.6. In 1 day-old lambs estimates of non-shivering thermogenesis, by the various methods, ranged from 0.8 to 1.4 l. O(2)/kg.hr (mean 1.1 l. or 31% of summit metabolism), and the estimates of shivering ranged from 1.3 to 1.9 l. O(2)/kg.hr (mean 1.6 l. or 46% of summit metabolism). However, in lambs 1-month old, estimates of non-shivering thermogenesis from sympathetic inhibition (0.6 and 0.8 l. O(2)/kg.hr) were considerably higher than estimates from muscular paralysis or stimulation by catecholamines (0.2 and 0.1 l. O(2)/kg.hr). It is suggested that the depression of summit metabolism by the sympathetic inhibitors is not solely due to specific inhibition of non-shivering thermogenesis, at least in the older lambs.7. The possession of a non-shivering thermogenic mechanism in addition to shivering is of clear survival value to new-born lambs.

Changes in plasma glucose, lactate and free fatty acids in lambs during summit metabolism and treatment with catecholamines

1. Exposure to cold increased the plasma levels of glucose and lactate in young lambs (< 1-63 days old). Free fatty acid concentrations also increased, the increase being much greater in lambs older than 20 days.2. Intravenous infusions of adrenaline and noradrenaline into lambs under a neutral thermal environment caused large increases in plasma glucose, lactate and free fatty acids.3. Adrenaline and noradrenaline infusions increased the concentration of palmitic, stearic and oleic acids in the plasma of young lambs.4. Treatment of lambs in summit metabolism with either alpha- or beta-adrenergic blocking agents (phentolamine or propranolol, respectively) caused the plasma levels of free fatty acids to fall. Phentolamine hydrochloride decreased the concentration of plasma glucose, but did not change the lactate level. In contrast, propranolol decreased the concentration of both of these metabolites in a significant proportion of the experiments.5. Induction of muscular paralysis by suxamethonium chloride, in lambs exposed to cold, resulted in a rise in plasma free fatty acids, and a fall in glucose and lactate levels.6. These observations suggest that the circulating level of plasma metabolites in young lambs is not the limiting factor in the metabolic response to cold exposure.

Oxygen consumption during pouch development of the macropod marsupial Setonix brachyurus

1. Measurements of O(2) consumption at 9 or 10 temperatures in the 20-40 degrees C ambient temperature range were made on joeys with ages selected to cover the 180-day period of pouch occupancy.2. The rate of O(2) consumption of joeys younger than 100 days increased directly with ambient temperature.3. After 100 days of age the O(2) consumption rate at low temperatures rose and at about 140 days of age a constant rate was maintained over the full ambient temperature range.4. Heat transfer from joey to mother commenced after 100 days of age.5. At 150-180 days of age the rate of O(2) consumption at 20 degrees C was approximately 12 times greater than at ages less than 100 days. A thermal neutral zone was established in the range 32-36 degrees C by joeys older than 150 days.6. At the usual pouch temperature of 36.5 degrees C, O(2) consumption per unit wet body weight rose from 12 ml./kg.min at birth to 17 ml./kg.min at the end of pouch life. On a unit dry body weight basis it fell from 120 to 56 ml./kg.min. This decline parallels the decrease in growth rate.

The blood flow and oxygen consumption of brown adipose tissue in the new-born rabbit

1. A direct method for measuring venous outflow from brown adipose tissue in anaesthetized new-born rabbits is described.2. During noradrenaline infusion the mean blood flow through brown adipose tissue increased from 87 to 360 ml./100 g tissue (wet wt.).min, and the mean rate of oxygen consumption of brown adipose tissue rose from 9.3 to 60 ml. O(2)/100 g tissue.min.3. During cold exposure the mean blood flow through brown adipose tissue increased from 90 to 304 ml./100 g tissue.min.4. The mean cardiac output was 266 ml./kg body weight.min; during noradrenaline infusion it was 405 ml./kg body weight.min. At rest about one tenth, and during noradrenaline infusion about one quarter of the cardiac output went to brown adipose tissue.5. It was calculated that most of the extra oxygen consumed during the metabolic response of the anaesthetized new-born rabbit to noradrenaline infusion or cold exposure was consumed by brown adipose tissue.6. Hypoxia (breathing 10% O(2) in N(2)) greatly reduced the increase in oxygen consumption but not the increase in blood flow in brown adipose tissue caused by noradrenaline infusion.