Energy Conservation Mechanism Research Articles

Adaptive traffic-based control method for energy conservation in wireless devices

Mobile units have many constraints for reliable communication in today’s mobile environments. Unlike wired networks in mobile networks, mobility induces frequent route changes. Energy conservation is an important issue that has to be taken into account for mobile devices. Every infrastructureless network must be adaptively self-configured particularly in terms of energy, connectivity, resource allocation and memory. Efficient utilization of battery power is important for wireless users because due to their movements their energy is fluctuating at different levels during operation mode. Traffic plays a major role for energy consumption because of the unpredictable incoming flow nature. Generally, the minimum transmission power required to keep the network connected achieves the optimal throughput performance in a dynamically changing topology network. In this paper an adaptive traffic-based control method for energy conservation is described and examined, which bounds an asynchronous operation where each node evaluates dissimilar sleep-wake schedules/states based on each node’s incoming sleep-history traffic. Simulation study is carried out for throughput, traffic characterization against performance and energy conservation evaluation of the proposed model taking into account a number of metrics and estimation of the effects of incrementing the sleep time duration to conserve energy. The proposed method could be applied to infrastructureless networks with any underlying routing protocol to provide independency, portability, as well as “fair” collaboration among energy conservation mechanism and routing protocol.

Torpor in Birds: Taxonomy, Energetics, and Ecology

Recent reports on patterns and occurrence of torpor and other natural hypothermic states in birds have prompted a revision of many longstanding opinions. For instance, a larger assortment of birds covering a wider range of body mass than previously recognized uses energy-conserving mechanisms in the face of abundant food supplies. Thus, although acute energetic stress triggers the occurrence of hypometabolic states in many birds, energy deficits can no longer be regarded as the sole stimulus for avian torpor. Additionally, the phenology of this phenomenon (phases, duration, depth) shows more interspecific variation than previously appreciated, and traditional concepts of the phases of torpor are not always adequate. Hence, inclusive definitions of torpor based on physiological and/or behavioral criteria have become more difficult to formulate. However, average nighttime body temperature, which is highly consistent throughout the class Aves (38.54 degrees +/- 0.96 degrees C, n = 202), provides a convenient reference for detecting natural hypothermic states. Of the putative ecological factors associated with avian torpor, food specialization seems a prime candidate as an ultimate factor in the occurrence of this state in birds. With few exceptions, all of these animals capable of torpor are either frugivorous, nectarivorous, or insectivorous, suggesting a correlation between thermoregulatory pattern and predictability of food supply. To date, no clear answer exists as to whether the variety of thermoregulatory patterns evident in birds involves discrete mechanisms or merely steps in a physiological continuum. However, I suggest that the occurrence of differences in torpor patterns among closely related species (e.g., within families) favors the latter interpretation.

Effects of ageing on the energy balance of food-restricted rats.

Age can alter energy balance by decreasing the resting metabolic rate. Food restriction can also change energy balance by decreasing energy expenditure as a mechanism of energy conservation. We investigated the influence of food restriction on the energy balance of rats at different ages. Wistar EPM-1 female rats were used at ages of 3, 9, 15 and 21 months. At each age, two food intake schedules were provided: control (ad libitum) and food restriction (50%). Animals remained under these schedules for 30 days, and throughout this period body weight, food intake, and stool collection were controlled daily. On the 30th day, animals were killed, blood was collected and the carcasses and faeces were processed for analysis by pump calorimetry. Blood glucose, T(3), T(4) and rT(3) levels were determined. Food restriction reduced energy gain and gross food efficiency of animals at different ages, but more so in older animals. Food-restricted rats also had lower energy expenditure than controls. This reduction was about 40% of the energy expenditure of control animals irrespective of age. Water content increased and fat content decreased in the carcass of food-restricted animals. Serum T(3) and T(4) levels were lower in food-restricted animals pointing out to a major role of thyroid hormones in the mechanism of energy conservation exhibited by food-restricted animals. The mechanism of energy conservation takes place in all restricted animals and is very important for survival and for species preservation, mainly in aged animals in which food restriction is frequently aggravated by senescence-related organic disorders.

Neuromodulation of the Perinatal Respiratory Network

Breathing movements are initiated and controlled by a neuronal network within the lower brainstem that is influenced by peripheral and suprapontine inputs. To provide adaptation of breathing to vocalisation, exercise or hypoxia, rhythmogenic neurons of the ventral respiratory group (VRG) within the ventrolateral medulla (VLM) are controlled by numerous neuromodulators. Underlying cellular mechanisms are currently analysed in respiratory active medulla preparations from perinatal rodents. This reveals properties of the perinatal respiratory network pivotal for understanding spontaneous or drug-induced perturbation of breathing in preterm and term infants. Already at birth, ligand-gated anion channels can inhibit VLM-VRG neurons. But impairment of Cl- extrusion by hormones or growth factors may interfere with respiratory functions. During severe hypoxia, resulting in anoxia of the VLM-VRG, perinatal respiratory activity persists for more than twenty minutes, although at a greatly reduced frequency. This frequency depression, associated with a hyperpolarisation of rhythmogenic VLM-VRG neurons, is reversed by K+ channel blockers, thyrotropin-releasing hormone or substance-P, for example. This response may represent an adaptive mechanism for energy conservation during oxygen depletion. Endogenous frequency depression of the normoxic perinatal respiratory rhythm, possibly mediated by endorphins or prostaglandins, may serve to dampen excessive respiratory activity in utero. Opiates and prostaglandins, known to impair breathing in infants during clinical administration, likely act directly to depress rhythmogenic VLM-VRG neurons. Based upon such findings in perinatal rodent models on synaptic inhibition and responses to hypoxia-anoxia or clinically-applicable drugs, novel pharmacological strategies are discussed that aim to stabilise infant breathing by targeting rhythmogenic respiratory neurons.

Group Hibernation Does Not Reduce Energetic Costs of Young Yellow‐Bellied Marmots

We investigated mechanisms of energy conservation during hibernation. The amount of time torpid was significantly less for groups of three young marmots than for marmots hibernating singly. Mean daily mass loss (DML; as mg d(-1) g(-1) immergence mass) averaged 1.33 for single marmots and 1.46 for grouped young. Animals were active 17.3% of the time, which used 82.4% of the energy, and were torpid 82.7% of the time, which used 17.6% of the energy expenditure. During longer torpor bouts, more time was spent in deep torpor, which decreased the hourly cost of a complete bout. Bout oxygen consumption V dot o2, percent time in deep torpor, and body temperature (T(B)) during deep torpor changed seasonally and were curvilinearly related to when in the hibernation period the measurements were made and probably represent a stage in the circannual metabolic cycle. The decrease of environmental temperature (T(E)) to 2 degrees C significantly increased metabolism. Potential costs of low T(E) were reduced by allowing T(B) to decrease, thereby reducing the T(B) to T(E) gradient. Average monthly metabolic rate was high early and late in the hibernation period when time spent euthermic was greater and when VO2 was higher. Over the hibernation period, energy saved averaged 77.1% and 88.0% of the costs for winter and summer euthermic metabolism, respectively. Hibernation costs were reduced by the seasonal changes, the high percentage of time in torpor, the rapid decline in V dot o2 following arousal, and allowing T(B) to decline at lower T(E). Asynchrony in the torpor cycles increased energy expenditures in group hibernators, which negated possible beneficial effects of group hibernation.

Does food quality influence thermoregulatory behavior in the intertidal fish Girella laevifrons?

Algal and invertebrate species are less abundant towards higher zones of the intertidal, where the greatest variations in physical environmental conditions occur. Mobile predators such as fishes that inhabit high intertidal rockpools are thus exposed to wide variations in physical conditions and to a low abundance and quality of food. We used an aquarium with a temperature gradient in the laboratory to assesed whether dietary quality differences modify temperature preferences of Girella laevifrons, one of the most abundant transitory fishes inhabiting rocky shores along the coast of Chile. Our results indicate that food quality clearly modifies temperature preferences in this species. Animals fed on high quality bivalves selected intermediate temperatures (16–18°C) while those fed on lower quality algae selected lower temperatures (10–12°C). Control fish not subjected to the temperature gradient did not select portions of the aquarium differentially. The thermal selectivity of G. laevifrons in relation to the optimization of digestive processes and mechanisms of energy conservation are discussed.

Nocturnal hypometabolism as an overwintering strategy of red deer (Cervus elaphus).

Herbivores of temperate and arctic zones are confronted during winter with harsh climatic conditions and nutritional shortness. It is still not fully understood how large ungulates cope with this twofold challenge. We found that red deer, similar to many other northern ungulates, show large seasonal fluctuations of metabolic rate, as indicated by heart rate, with a 60% reduction at the winter nadir compared with the summer peak. A previously unknown mechanism of energy conservation, i.e., nocturnal hypometabolism associated with peripheral cooling, contributed significantly to lower energy expenditure during winter. Predominantly during late winter night and early morning hours, subcutaneous temperature could decrease substantially. Importantly, during these episodes of peripheral cooling, heart rate was not maintained at a constant level, as to be expected from classical models of thermoregulation in the thermoneutral zone, but continuously decreased with subcutaneous temperature, both during locomotor activity and at rest. This indicates that the circadian minimum of basal metabolic rate and of the set-point of body temperature regulation varied and dropped to particularly low levels during late winter. Our results suggest, together with accumulating evidence from other species, that reducing endogenous heat production is not restricted to hibernators and daily heterotherms but is a common and well-regulated physiological response of endothermic organisms to energetically challenging situations. Whether the temperature of all tissues is affected, or the body shell only, may simply be a result of the duration and degree of hypometabolism and its interaction with body size-dependent heat loss.

A novel membrane-bound Ech [NiFe] hydrogenase in Desulfovibrio gigas

In the present study, we report the identification of an operon with six coding regions for a multisubunit membrane-bound [NiFe] hydrogenase in the genome of Desulfovibrio gigas. Sequence analysis of the deduced polypeptides reveals a high similarity to subunits of proteins belonging to the family of Ech hydrogenases. The operon is organised similarly to the operon coding for the Ech hydrogenase from Methanosarcina barkeri, suggesting that both encode very similar hydrogenases. Expression of the operon was detected by Northern blot and RT-PCR analyses, and the presence of the encoded proteins was examined by Western blotting. The possible role of this hydrogenase is discussed, relating it with a potential function in the H 2 cycling as a mechanism for energy conservation in D. gigas. The present study provides therefore valuable insights into the open question of the energy conserving mechanism in D. gigas.

Stroke frequencies of emperor penguins diving under sea ice.

During diving, intermittent swim stroke patterns, ranging from burst/coast locomotion to prolonged gliding, represent potential energy conservation mechanisms that could extend the duration of aerobic metabolism and, hence, increase the aerobic dive limit (ADL, dive duration associated with onset of lactate accumulation). A 5.6 min ADL for emperor penguins had been previously determined with lactate measurements after dives of <50 m depth. In order to assess locomotory patterns during such dives, longitudinal acceleration was measured with an attached accelerometer in 44 dives of seven adult birds diving from an isolated dive hole in the sea ice of McMurdo Sound, Antarctica. Detection of wing strokes in processed accelerometer data was verified in selected birds with analysis of simultaneous Crittercam underwater video footage. Mean dive duration of birds equipped with the accelerometer and a time-depth recorder (TDR) was 5.7+/-2.2 min; 48% of these dives were greater than the measured 5.6 min ADL (ADL(M)). Highest stroke frequencies (0.92+/-0.31 Hz, N=981) occurred during the initial descent to 12 m depth. Swimming effort was reduced to a mean stroke frequency <0.70 Hz during other phases of the dive (while traveling below 12 m depth, during foraging ascents/descents to and from the sub-ice surface, and during final ascents to exit). The longest stroke interval (8.6 s) occurred during a feeding excursion to the undersurface of the ice. In dives >ADL(M), mean stroke frequency during travel segments was significantly less than that in dives <ADL(M) (P<0.05). Mean stroke frequency of the entire dive correlated inversely (P<0.05) with diving duration (r=-0.67) and with mean dive depth (r=-0.43). Emperor penguins did not exhibit any significant (>10 s) periods of prolonged gliding during these shallow (<60 m) foraging dives. However, a stroke/glide pattern was evident with more than 50% of strokes associated with a stroke interval >1.6 s, and with lower stroke frequency associated with increased dive duration.

Preface

An Advanced FEBS Course “Mitochondria in the Cell Life and Death” has taken place in Moscow on 2–7 September, 2001. Lecturers from 10 countries presented 19 reports to the 64 participants from 11 countries. In addition to the official participants, many students, postgraduates, and researchers of Moscow State University (MSU) attended the meeting and actively participated in discussions. This was facilitated by the fact that the Course was held in the University campus, namely in the new Laboratory Building B, the construction of which was completed quite recently. Here a novel MSU School of Bioengineering and Bioinformatics is located. The following topics were discussed: mechanisms of energy conservation and dissipation, mitochondria and apoptosis, and mitochondria and diseases. Below the readers can find selected minireviews devoted to regulatory and pathological aspects of these topics.

Ecological and Evolutionary Physiology of Desert Birds: A Progress Report

The adaptive significance of mechanisms of energy and water conservation among species of desert rodents, which avoid temperature extremes by remaining within a burrow during the day, is well established. Conventional wisdom holds that arid-zone birds, diurnal organisms that endure the brunt of their environment, occupy these desert climates because of the possession of physiological design features common to all within the class Aves. We review studies that show that desert birds may have evolved specific features to deal with hot desert conditions including: a reduced basal metabolic rate (BMR) and field metabolic rate (FMR), and lower total evaporative water loss (TEWL) and water turnover (WTO).Previous work on the comparative physiology of desert birds relied primarily on information gathered on species from the deserts of the southwestern U.S., which are semi-arid habitats of recent geologic origin. We include data on species from Old World deserts, which are geologically older than those in the New World, and place physiological responses along an aridity axis that includes mesic, semi-arid, arid, and hyperarid environments.The physiological differences between desert and mesic birds that we have identified using the comparative method could arise as a result of acclimation to different environments, of genetic change mediated by selection, or both. We present data on the flexibility of BMR and TEWL in Hoopoe Larks that suggest that phenotypic adjustments in these variables can be substantial. Finally, we suggest that linkages between the physiology of individual organism and its life-history are fundamental to the understanding of life-history evolution.

A method to determine mechanical energy conservation and efficiency in equine gait: a preliminary study.

Metabolic and mechanical energy costs of locomotion can be combined to calculate locomotor efficiency, which is the quotient of the mechanical energy and metabolic costs. The purpose of this pilot study was to evaluate the mechanical and metabolic energy costs of locomotion at a range of 7 trotting speeds (2.5 to 6.2 m/s) on a level treadmill. A single, sound Thoroughbred horse was modelled as a system of 15 linked segments incorporating all 4 limbs, head, neck and trunk. The horse performed a continuous incremental exercise test at increasing trotting speeds while VO2 was recorded using a breath-by-breath gas analysis system. Positional data were recorded concurrently at 100 Hz using a 2-camera infrared kinematic system. Mechanical energy cost was calculated for 3-6 strides per speed increment, and metabolic data were obtained during the last 15 s of each speed step. Mechanical energy cost increased linearly from 3.3 J/kg/m at 2.5 m/s to a value of 5.31 J/kg/m at 6.2 m/s, and the within-subject variability was low at each of the speed steps. This analysis accounted for the important energy-conserving mechanisms of energy exchange within and between segments of the link segment model. Within-segment energy conservation remained approximately constant as speed increased, whereas between-segment conservation increased from 1040 to 4502 J/stride. The combination of both metabolic and mechanical costs of locomotion yielded an inverted bell-shaped curve of 'apparent' efficiency across the speed increments, with the maximum value occurring when metabolic cost was lowest at 3.8 m/s.

Short-term effects of a hypocaloric diet on nitrogen excretion in morbid obese women.

To determine whether the daily pattern of urine excretion of N wastes is affected by obesity and very low-calorie diets (VLCD). The plasma amino acid, urea and other energy parameters, as well as the urinary excretion of total nitrogen, urea and creatinine were studied in obese and normal-weight women. The obese women's data were obtained under hospital basal controlled conditions (8.1 MJ/day) and after 3 days of VLCD diet (1.9 MJ/day) controls were studied only once (5.8 MJ/day). The hourly excretion patterns of total N, urea and creatinine were determined from the composition of each bladder voiding. Twenty morbidly obese and 10 age-matched normal-weight control women. Plasma amino acid levels were higher in obese women, which showed a limited ability to metabolize amino acid hydrocarbon skeletons. Neither differences in the patterns between groups nor total 24 h values for urine volume were found. Total N and urea excretion diminished under VLCD diet. Hourly creatinine excretion showed a flat pattern and was higher in obese women than in the controls, VLCD diet diminished the amount of creatinine excreted in 24 h. The early change in energy availability that the creatinine excretion figures reflect may result from the energy conservation mechanisms induced in response to energy restriction. The early onset of this effect (3 days, and the extent of decrease (approximately 19%) also suggest that the impact of VLCD on the muscle energy budget of the obese is more marked than usually assumed.

Energy expenditure of rats subjected to long-term food restriction

Food restriction, even when expressed per unit of metabolic mass, leads to energy conservation as seen by decreased oxygen consumption. The objective of the present study was to verify whether the energy conservation mechanism reduces energy expenditure for as long as food restriction lasts or whether a return to basal level may occur without realimentation, mainly in mildly food-restricted rats. Wistar rats were brought to the laboratory on weaning. They were then assigned to control group that received ad libitum food intake, R 10 and R 20 groups that received 90 and 80%, respectively, of the food eaten by control group and R M group that received an amount of food enough only to keep body weight. The food restriction period lasted for 3 months and was followed by another month during which all groups received ad libitum food intake. The results showed that even in animals subjected to mild food restriction (10%) there was a sustained decrease in oxygen consumption that lasted until refeeding of the animals. The results led to the conclusion that the energy conservation mechanism is active from little food restriction until more stronger levels of restriction, in a proportional manner, and the decreased energy expenditure is maintained during the whole food restriction period.

Molecular Cloning of the Gene Encoding Flavoredoxin, a Flavoprotein from Desulfovibrio gigas

Sulfate-reducing bacteria are rich in unique redox proteins and electron carriers that participate in a variety of essential pathways. Several studies have been carried out to characterize these proteins, but the structure and function of many are poorly understood. Many Desulfovibrio species can grow using hydrogen as the sole energy source, indicating that the oxidation of hydrogen with sulfite as the terminal electron acceptor is an energy-conserving mechanism. Flavoredoxin is an FMN-binding protein isolated from the sulfate-reducing bacteria Desulfovibrio gigas that participates in the reduction of bisulfite from hydrogen. Here we report the cloning and sequencing of the flavoredoxin gene. The derived amino acid sequence exhibits similarity to several flavoproteins which are members of a new family of flavin reductases suggested to bind FMN in a novel mode.

Daily torpor in the gray mouse lemur (Microcebus murinus) in Madagascar: energetic consequences and biological significance.

Patterns and energetic consequences of spontaneous daily torpor were measured in the gray mouse lemur (Microcebus murinus) under natural conditions of ambient temperature and photoperiod in a dry deciduous forest in western Madagascar. Over a period of two consecutive dry seasons, oxygen consumption (VO2) and body temperature (T b) were measured on ten individuals kept in outdoor enclosures. In all animals, spontaneous daily torpor occurred on a daily basis with torpor bouts lasting from 3.6 to 17.6 h, with a mean torpor bout duration of 9.3 h. On average, body temperatures in torpor were 17.3±4.9°C with a recorded minimum value of 7.8°C. Torpor was not restricted to the mouse lemurs' diurnal resting phase: entries occurred throughout the night and arousals mainly around midday, coinciding with the daily ambient temperature maximum. Arousal from torpor was a two-phase process with a first passive, exogenous heating where the T b of animals increased from the torpor T b minimum to a mean value of 27.1°C before the second, endogenous heat production commenced to further raise T b to normothermic values. Metabolic rate during torpor (28.6±13.2 ml O2 h-1) was significantly reduced by about 76% compared to resting metabolic rate (132.6±50.5 ml O2 h-1). On average, for all M. murinus individuals measured, hypometabolism during daily torpor reduced daily energy expenditure by about 38%. In conclusion, all these energy-conserving mechanisms of the nocturnal mouse lemurs, with passive exogenous heating during arousal from torpor, low minimum torpor T bs, and extended torpor bouts into the activity phase, comprise an important and highly adapted mechanism to minimize energetic costs in response to unfavorable environmental conditions and may play a crucial role for individual fitness.

THERMAL BIOLOGY AND METABOLISM OF THE AMERICAN SHREW-MOLE,NEUROTRICHUS GIBBSII

The American shrew-mole (Neurotrichus gibbsii) seems to occupy an ecological and evolutionary position intermediate to that of shrews and fully fossorial moles. However, because little is known regarding their physiology, we examined the metabolic rate and thermoregulatory competence of 6 shrew-moles exposed to ambient temperatures ranging from 3 to 34°C with flow-through respirometry. The basal rate of metabolism of N. gibbsii (3.94 ml O2 g−1 h−1; 77.90 J g−1 h−1) was 2.32 times greater than predicted for similar-sized placental mammals and close to that of soricine shrews of comparable mass (10–12 g). Over the entire range of test temperatures, mean body temperature (38.4 ± 0.2°C SE) of this small semiterrestrial talpid was higher and more labile than that of other North American moles but within the range typical for north-temperate soricids. With declining ambient temperatures, shrew-moles exhibited gradual reductions in body temperature and minimal whole-body thermal conductance. In 2 instances, shrew-moles were observed to enter an apparent state of hypometabolism. Whether the observed reductions in body temperature and metabolic rate of Neurotrichus exposed to low ambient temperatures are adaptive energy-conservation mechanisms exhibited during periods of prolonged cool wet weather and food deficits in nature, or simply reflect an inability to proficiently thermoregulate after an extended fast, is currently unknown.

Kinetic Characterization of Mitochondrial Complex I Inhibitors Using Annonaceous Acetogenins

The NADH:ubiquinone oxidoreductase (complex I) of the mitochondrial respiratory chain is by far the largest and most complicated of the proton-translocating enzymes involved in the oxidative phosphorylation. Many clues regarding the electron pathways from matrix NADH to membrane ubiquinone and the links of this process with the translocation of protons are highly controversial. Different types of inhibitors become valuable tools to dissect the electron and proton pathways of this complex enzyme. Therefore, further knowledge of the mode of action of complex I inhibitors is needed to understand the underlying mechanism of energy conservation. This study presents for the first time a detailed exploration of the inhibitory action of the Annonaceous acetogenins, the most powerful inhibitors of the mammalian enzyme, taking as the head-series rolliniastatin-1, rolliniastatin-2, and corossolin. Despite their close chemical resemblance, each of them inhibits the complex I with different kinetic features reflecting differential binding to the enzyme.

Bioenergetics of the Archaea.

In the late 1970s, on the basis of rRNA phylogeny, Archaea (archaebacteria) was identified as a distinct domain of life besides Bacteria (eubacteria) and Eucarya. Though forming a separate domain, Archaea display an enormous diversity of lifestyles and metabolic capabilities. Many archaeal species are adapted to extreme environments with respect to salinity, temperatures around the boiling point of water, and/or extremely alkaline or acidic pH. This has posed the challenge of studying the molecular and mechanistic bases on which these organisms can cope with such adverse conditions. This review considers our cumulative knowledge on archaeal mechanisms of primary energy conservation, in relationship to those of bacteria and eucarya. Although the universal principle of chemiosmotic energy conservation also holds for Archaea, distinct features have been discovered with respect to novel ion-transducing, membrane-residing protein complexes and the use of novel cofactors in bioenergetics of methanogenesis. From aerobically respiring Archaea, unusual electron-transporting supercomplexes could be isolated and functionally resolved, and a proposal on the organization of archaeal electron transport chains has been presented. The unique functions of archaeal rhodopsins as sensory systems and as proton or chloride pumps have been elucidated on the basis of recent structural information on the atomic scale. Whereas components of methanogenesis and of phototrophic energy transduction in halobacteria appear to be unique to Archaea, respiratory complexes and the ATP synthase exhibit some chimeric features with respect to their evolutionary origin. Nevertheless, archaeal ATP synthases are to be considered distinct members of this family of secondary energy transducers. A major challenge to future investigations is the development of archaeal genetic transformation systems, in order to gain access to the regulation of bioenergetic systems and to overproducers of archaeal membrane proteins as a prerequisite for their crystallization.

Influence of torpor on milk protein composition and secretion in lactating bats.

In the pipistrelle bat (Pipistrellus pipistrellus), the metabolic load of lactation is not met to any significant extent by increased food intake or mobilization of body reserves, and aerial foraging accounts for most of the animal's energy expenditure even during lactation. Energy conservation must, therefore, play a critical role in maintaining lactation. The principal mechanism for energy conservation appears to be the bat's ability to enter torpor, but this may itself interrupt milk synthesis and secretion unless the pipistrelle mammary gland is adapted to counteract its effect. The effect of torpor on mammary tissue function was studied in mammary tissue explant cultures prepared in weeks 1-3 of lactation, when milk water yield was 0.20, 0.88, and 0.30 mL/d respectively. Protein synthesis measured by incorporation of radiolabeled amino acids was 44% lower (P < 0.001) in bat tissue explants cultured at ambient temperature (22 degrees C) compared with 37 degrees C. The reduction was similar to that observed in mouse mammary tissue (57%) and was unaffected by stage of lactation. Analysis of explant protein after [35S]methionine labelling showed the majority of proteins synthesised in culture to be milk proteins; it also demonstrated that the decrease in protein synthesis at ambient temperature was a general phenomenon: synthesis of both secretory and intracellular mammary proteins was reduced at the lower culture temperature. The results suggest that bat mammary tissue has no mechanism to counteract the effect of reduced body temperature and that periods of lactational torpor are likely to cause a pronounced diurnal variation in the rate of milk secretion.