The adult lifespan of the female honey bee (Apis mellifera): Metabolic rate, AGE pigment and the effect of dietary fatty acids.

Female honey bees can be queens or workers and although genetically identical, workers have an adult lifespan of weeks while queens can live for years. The mechanisms underlying this extraordinary difference remain unknown. This study examines three potential explanations of the queen-worker lifespan difference. Metabolic rates were similar in age-matched queens and workers and thus are not an explanation. The accumulation of fluorescent AGE pigment has been successfully used as a good measure of cellular senescence in many species. Unlike other animals, AGE pigment level reduced during adult life of queens and workers. This unusual finding suggests female honey bees can either modify, or remove from their body, AGE pigment. Another queen-worker difference is that, as adults, workers eat pollen but queens do not. Pollen is a source of polyunsaturated fatty acids. Its consumption explains the queen-worker difference in membrane fat composition of female adult honey bees which has previously been suggested as a cause of the lifespan difference. We were able to produce "queen-worker" membrane differences in workers by manipulation of diet that did not change worker lifespan and we can, thus, also rule out pollen consumption by workers as an explanation of the dramatic queen-worker lifespan difference.

A Comparative Study of Hummingbirds and Chickens Provides Mechanistic Insight on the Histidine Containing Dipeptide Role in Skeletal Muscle Metabolism.

Histidine containing dipeptides (HCDs) have numerous ergogenic and therapeutic properties, but their primary role in skeletal muscle remains unclear. Potential functions include pH regulation, protection against reactive oxygen/nitrogen species, or Ca2+ regulation. In recognition of the challenge of isolating physiological processes in-vivo, we employed a comparative physiology approach to investigate the primary mechanism of HCD action in skeletal muscle. We selected two avian species (i.e., hummingbirds and chickens), who represented the extremes of the physiological processes in which HCDs are likely to function. Our findings indicate that HCDs are non-essential to the development of highly oxidative and contractile muscle, given their very low content in hummingbird skeletal tissue. In contrast, their abundance in the glycolytic chicken muscle, indicate that they are important in anaerobic bioenergetics as pH regulators. This evidence provides new insights on the HCD role in skeletal muscle, which could inform widespread interventions, from health to elite performance.

Cloning and functional characterization of an uncoupling protein homolog in hummingbirds.

The cDNA of an uncoupling protein (UCP) homolog has been cloned from the swallow-tailed hummingbird, Eupetomena macroura. The hummingbird uncoupling protein (HmUCP) cDNA was amplified from pectoral muscle (flight muscle) using RT-PCR and primers for conserved domains of various known UCP homologs. The rapid amplification of cDNA ends (RACE) method was used to complete the cloning of the 5' and 3' ends of the open reading frame. The HmUCP coding region contains 915 nucleotides, and the deduced protein sequence consists of 304 amino acids, being approximately 72, 70, and 55% identical to human UCP3, UCP2, and UCP1, respectively. The uncoupling activity of this novel protein was characterized in yeast. In this expression system, the 12CA5-tagged HmUCP fusion protein was detected by Western blot in the enriched mitochondrial fraction. Similarly to rat UCP1, HmUCP decreased the mitochondrial membrane potential as measured in whole yeast by uptake of the fluorescent potential-sensitive dye 3',3-dihexyloxacarbocyanine iodide. The HmUCP mRNA is primarily expressed in skeletal muscle, but high levels can also be detected in heart and liver, as assessed by Northern blot analysis. Lowering the room's temperature to 12-14 degrees C triggered the cycle torpor/rewarming, typical of hummingbirds. Both in the pectoral muscle and heart, HmUCP mRNA levels were 1.5- to 3.4-fold higher during torpor. In conclusion, this is the first report of an UCP homolog in birds. The data indicate that HmUCP has the potential to function as an UCP and could play a thermogenic role during rewarming.

Development of compensatory thermogenesis in response to overfeeding in hypothyroid rats.

Intact or surgically thyroidectomized (Tx) adult male Wistar rats, weighing 150-200 g, were fed a standard chow diet (approximately 1.8 Cal/g) or a high calorie (approximately 3.8 Cal/g) diet (cafeteria diet) for up to 30 days. Daily energy intake was about 5-fold higher in the rats fed the cafeteria diet regardless of their thyroid status. The cafeteria diet caused the retroperitoneal white fat pad to increase by approximately 2-fold, the volume of isolated white adipocytes to increase by 2-fold, and the total body fat to increase by a factor of approximately 3, again regardless of thyroid status. It also increased basal metabolic rate by about 20% in intact rats and by about 50% in Tx rats. The brown fat thermal response to norepinephrine (NE) infusion was approximately 2-fold increased in the intact rats fed the cafeteria diet. However, in the Tx rats, the brown fat thermal response to NE was blunted regardless of the dietary regimen adopted. In both intact and Tx rats, the cafeteria diet increased total brown fat mitochondria, uncoupling protein percentage, and total brown fat uncoupling protein by about 3-, 2-, and 5-fold, respectively. Serum leptin levels also increased approximately 4-fold in intact rats fed the cafeteria diet. However, in Tx rats, leptin levels did not change significantly during overfeeding. In conclusion, hypothyroidism caused the brown fat to become unresponsive to NE, even after 1 month on the cafeteria diet. However, these rats were able to increase basal metabolic rate and, as assessed by several different parameters, did not gain fat beyond that observed in intact controls kept on a similar overfeeding schedule.

Thermogenesis in birds.

The article discusses the importance of avian skeletal muscle as a source for heat generation by means of both shivering and non-shivering. Non-shivering thermogenesis in birds is still a polemic issue. Recent evidence at the molecular/cellular level indicates, however, that this type of heat generation may also exist among birds. The involvement of the sarcoplasmic reticulum calcium ATPase in non-shivering thermogenesis is discussed in-depth.

Air sac temperature and acid-base balance during thermal panting in ducks.

Ducks become slightly hyperthermic at ambient temperatures (TA) above 35 degrees C, as indicated by cloacal temperature measurements. The air sacs do not represent important sites of evaporation, since their wall and air temperatures are not lower than ambient and body (cloacal) temperatures during thermal panting. Upon exposure to moderate heat loads (TA = 35 degrees C), arterial PO2 and PCO2 are relatively constant, whereas pH increases slightly. During exposure to heavy heat loads (TA = 42 degrees C), however, ducks become alkalotic, as indicated by a significant increase in arterial pH.

Physiological constraints in the aerobic performance of hummingbirds.

Hovering flight has been described as the most energetically expensive form of locomotion. Among the vertebrates, hummingbirds weighing only 1.5-20 g are the elite practitioners of this aerial art. Their flight muscles are, therefore, the most oxygen demanding locomotor muscles per unit tissue mass of all vertebrates. Tissue level functional and structural adaptations for oxygen transport are compared between hummingbirds and mammals in this paper. Hummingbirds present extreme structural adaptations in their flight muscles. Mitochondrial densities greater than 30% are observed in their pectoral muscles, and the surface area of the inner membrane of their mitochondria is twice that of mammals. This doubling of their mitochondrial oxidative capacity is accompanied by a proportional increase in the specific activity (per g tissue) of the mitochondrial manganese superoxide dismutase (SOD-Mn) in their flight muscles, thus indicating that oxygen toxicity is not a constraint in the aerobic performance of hummingbirds during hovering flight. Finally, the liver appears to play a major role in providing the necessary substrates for their high aerobic performance, and also in eliminating the oxygen free radicals formed during oxidative phosphorylation.

Further analysis of open-respirometry systems: an a-compartmental mechanistic approach.

A system is said to be "instantaneous" when for a given constant input an equilibrium output is obtained after a while. In the meantime, the output is changing from its initial value towards the equilibrium one. This is the transient period of the system and transients are important features of open-respirometry systems. During transients, one cannot compute the input amplitude directly from the output. The existing models (e.g., first or second order dynamics) cannot account for many of the features observed in real open-respirometry systems, such as time lag. Also, these models do not explain what should be expected when a system is speeded up or slowed down. The purpose of the present study was to develop a mechanistic approach to the dynamics of open-respirometry systems, employing basic thermodynamic concepts. It is demonstrated that all the main relevant features of the output dynamics are due to and can be adequately explained by a distribution of apparent velocities within the set of molecules travelling along the system. The importance of the rate at which the molecules leave the sensor is explored for the first time. The study approaches the difference in calibrating a system with a continuous input and with a "unit impulse": the former truly reveals the dynamics of the system while the latter represents the first derivative (in time) of the former and, thus, cannot adequately be employed in the apparent time-constant determination. Also, we demonstrate why the apparent order of the output changes with volume or flow.

Ion fluxes and hematological parameters of two teleosts from the Rio Negro, Amazon, exposed to hypoxia.

The aim of this study was to describe the effect of hypoxia on whole body ion fluxes and hematological parameters in two Amazonian teleosts: Serrasalmus eigenmanni and Metynnis hypsauchen. The increase of Na+ and Cl- effluxes on M. hypsauchen exposed to hypoxia may be related to an increase of gill ventilation and effective respiratory surface area, to avoid a reduction in the oxygen uptake, and/or with the decrease of pHe, that could inhibit Na+ and Cl- transporters and, therefore, reduce influx of these ions. Effluxes of Na+ and Cl- were lower in hypoxia than in normoxia for S. eigenmanni, possibly because in hypoxia this species would reduce gill ventilation and oxygen uptake, which would lead to a decrease of gill ion efflux and, consequently, reducing ion loss. The increase on hematocrit (Ht) during hypoxia in M. hypsauchen probably was caused by an increase of the red blood cell volume (MCV). For S. eigenmanni the increase on glucose possibly results from the usage of glucose reserve mobilization. Metynnis hypsauchen showed to be more sensitive to hypoxia than Serrasalmus eigenmanni, since the first presented more significant alterations on these osmoregulatory and hematological parameters. Nevertheless, the alterations observed for both species are strategies adopted by fishes to preserve oxygen supply to metabolizing tissues during exposure to hypoxia.

A morphometric study of the tracheal system of Peripatus acacioi Marcus and Marcus (Onychophora).

Volumes and surfaces of the tracheal system in Peripatus acacioi Marcus and Marcus (Onychophora) were evaluated using stereological techniques. The onychophorans were divided into three portions, arbitrarily denominated lead, body and tail segments. This procedure was used to provide information on the spatial distribution of tracheal tubes along the body. The mean weight specific tracheal volume for a 212 mg animal (average body weight) was 7.27 microliters g-1. Size appears to affect tracheal volume; the surface density of the tracheal system was greater in both lead and tail segments. There appears to be a positive correlation between tracheal surface density and tissue metabolic activity.

The signal in total-body plethysmography: errors due to adiabatic-isothermic difference.

Total-body plethysmography is a technique often employed in comparative physiology studies because it avoids excessive handling of the animals. The pressure signal obtained is generated by an increase in internal energy of the gas phase of the system. Currently, this increase in internal energy is ascribed to heating (and water vapour saturation) of the inspired gas. The standard equation for computing tidal-volume implies that only temperature and saturation differences can be responsible for generating the ventilation signal. In this study, we were able to demonstrate that the difference between the external process of the thoracic expansion, which is adiabatic, and the internal process of it, which is isothermic, is an important factor of internal energy change in the total-body plethysmography method. In other words, organic tissues transfer heat to the entering gas but also to the present gas, in a way that keeps internal expansion an isothermic process. This extra amount of energy was never taken into account before. Therefore, experiments using such a technique to measure tidal-volume should be done using isothermic chambers. Moreover, due to uncertainties of the complementary measurements (ambient and lung temperatures, ambient water vapour saturation) needed to compute tidal-volume using total-body plethysmography, a minimal temperature difference about 15 degrees C between body and ambient should exist to keep uncertainties in tidal-volume values below 5%. However, this limit is not absolute, because it varies as a function of humidity and degree of uncertainty of the complementary measurements.

The oxygen gain of diving insects.

The gas gill of diving insects allows gas exchange with the surrounding water, thus extending diving time. Incompressible gas gills can potentially last indefinitely underwater, but compressible gas gills have a definite lifetime. Theoretical models of a dive event have reached opposite conclusions about the oxygen gain (G, the ratio between the duration of the diving event and the time that the initial oxygen content of the bubble would allow the insect to stay underwater). While some authors claim that G has a fixed value independently of the parameters of the dive (e.g. oxygen consumption rate) others claim the contrary. However, these claims are based on numerical solutions of the models. In this study we offer an analytical solution to the problem. The analysis of a model with constant area for gas exchange demonstrates that G cannot have a fixed value, for a fixed gain would imply in a P(O(2)) inside the bubble different from the one occurring as a result of physical constraints of the gas exchange process.

Structural determinants of maximal O2 transport in muscles of exercising foxes.

The arctic blue fox (Alopex lagopus) has a specific maximal oxygen consumption (VO2 max/Mb = 3.6 ml O2.s-1.kg-1) that is approximately 1.6-fold greater than those of dogs and horses. The fox has one of the highest body mass specific skeletal muscle mitochondrial volumes (V(mt,m)/Mb = 44 cm3.kg-1) among mammalian athletic species matching its higher VO2 max/Mb. The structural components related to capillaries, such as specific capillary length density (J(c)/Mb = 348 km.kg-1) and specific capillary volume (V(c)/Mb = 4.8 ml.kg-1), are not greater in the fox than in the larger athletes. Because a greater specific muscle diffusing capacity for oxygen (DTO2/Mb) is not utilized by the fox to achieve a higher VO2 max/Mb, a higher pressure difference for diffusion in the muscle capillaries is the alternative explanation for the fox's higher VO2 max/Mb. This mechanism is suggested by the fox's higher arterial and mixed venous capillary PO2 (120 mm Hg and 37 mm Hg, respectively) and its shorter mean muscle capillary transit time for blood (tc = 0.28 sec) compared to larger species.

Development of blood pressure and cardiac reflexes in the frog Pseudis paradoxsus.

Systemic arterial blood pressure and heart rate (fH) were measured in unanesthetized, unrestrained larvae and adults of the paradoxical frog, Pseudis paradoxus from São Paulo State in Brazil. Four developmental groups were used, representing the complete transition from aquatic larvae to primarily air-breathing adults. fH (49-66 beats/min) was not significantly affected by development, whereas mean arterial blood pressure was strongly affected, being lowest in the stage 37-39 larvae (10 mmHg), intermediate in the stage 44-45 larvae (18 mmHg), and highest in the juveniles and adults (31 and 30 mmHg, respectively). Blood pressure was not significantly correlated with body mass, which was greatest in the youngest larvae and smallest in the juveniles. In the youngest larvae studied (stages 37-39), lung ventilation was infrequent, causing a slight decrease in arterial blood pressure but no change in heart rate. Lung ventilation was more frequent in stages 44-45 larvae and nearly continuous in juveniles and adults floating at the surface. Bradycardia during both forced and voluntary diving was observed in almost every advanced larva, juvenile, and adult but in only one of four young larvae. Developmentally related changes in blood pressure were not complete until metamorphosis, whereas diving bradycardia was present at an earlier stage.

High rate of O2 consumption in exercising foxes: large PO2 difference drives diffusion across the lung.

The fox has one of the highest mass specific rates of maximal oxygen consumption (VO2max/Mb) that has been measured, yet its specific pulmonary diffusing capacity (DLO2/Mb, measured morphometrically) is similar to that of most mammalian species. It achieves a high O2 flux per unit DLO2 with a large partial pressure difference driving O2 diffusion from alveolar gas to capillary blood (PAO2-PbO2). This paper explores the mechanisms that the fox utilizes to achieve this large pressure difference and the extent to which it exploits its structural diffusing capacity. Foxes were exercised on a treadmill at maximal rates of O2 uptake. The following parameters were measured or calculated: arterial and mixed venous PO2, PCO2, pH and O2 concentration of the blood, cardiac output, hemoglobin concentration and O2 equilibrium curve of the blood, and morphometric estimates of pulmonary capillary volume and pulmonary diffusing capacity for O2. These data were used to calculate pulmonary capillary transit time and the time course of the change in O2 concentration and PO2 of the blood as it transits the lung. The fox has a morphometric pulmonary diffusing capacity of 0.098 ml O2.sec-1.mm Hg-1.kg-1. At VO2 max (3.6 ml O2.sec-1.kg-1) the fox hyperventilates, resulting in a high PAO2 (124 mm Hg); it also maintains a low PbO2 (88 mm Hg) by having a short transit time (0.13 sec) due to a high specific cardiac output (25 ml.sec-1.kg-1). Our calculations indicate that at VO2max the fox uses almost all of the pulmonary capillary transit time for O2 equilibration, in contrast to other species.

Capillary blood transit time in muscles in relation to body size and aerobic capacity.

The mean minimal transit time for blood in muscle capillaries (tc) was estimated in six species, spanning two orders of magnitude in body mass and aerobic capacity: horse, steer, dog, goat, fox and agouti. Arterial (CaO2) and mixed venous (CvO2) blood O2 concentrations, blood hemoglobin concentrations ([Hb]) and oxygen uptake rates were measured while the animals ran on a treadmill at a speed that elicited the maximal oxygen consumption rate (VO2max) from each animal. Blood flow to the muscles (Qm) was assumed to be 85% of cardiac output, which was calculated using the Fick relationship. Total muscle capillary blood volume (Vc) and total muscle mitochondrial volume were estimated by morphometry, using a whole-body muscle sampling scheme. The tc was computed as Vc/Qm. The tc was 0.3-0.5 s in the 4 kg foxes and agoutis, 0.7-0.8 s in the 25 kg dogs and goats, and 0.8-1.0 s in the 400 kg horses and steers. The tc was positively correlated with body mass and negatively correlated with transcapillary O2 release rate per unit capillary length. Mitochondrial content was positively correlated with VO2max and with the product of Qm and [Hb]. These data suggested that Qm, Vc, maximal hemoglobin flux, and consequently tc, are co-adjusted to result in muscle O2 supply conditions that are matched to the O2 demands of the muscles at VO2max.

Ion fluxes and hematological parameters of two teleosts from the Rio Negro, Amazon, exposed to hypoxia / Fluxos iônicos e parâmetros hematológicos em duas espécies de teleósteos do Rio Negro, Amazônia, expostos à hipoxia

The aim of this study was to describe the effect of hypoxia on whole body ion fluxes and hematological parameters in two Amazonian teleosts: Serrasalmus eigenmanni and Metynnis hypsauchen. The increase of Na+ and Cl- effluxes on M. hypsauchen exposed to hypoxia may be related to an increase of gill ventilation and effective respiratory surface area, to avoid a reduction in the oxygen uptake, and/or with the decrease of pHe, that could inhibit Na+ and Cl- transporters and, therefore, reduce influx of these ions. Effluxes of Na+ and Cl- were lower in hypoxia than in normoxia for S. eigenmanni, possibly because in hypoxia this species would reduce gill ventilation and oxygen uptake, which would lead to a decrease of gill ion efflux and, consequently, reducing ion loss. The increase on hematocrit (Ht) during hypoxia in M. hypsauchen probably was caused by an increase of the red blood cell volume (MCV). For S. eigenmanni the increase on glucose possibly results from the usage of glucose reserve mobilization. Metynnis hypsauchen showed to be more sensitive to hypoxia than Serrasalmus eigenmanni, since the first presented more significant alterations on these osmoregulatory and hematological parameters. Nevertheless, the alterations observed for both species are strategies adopted by fishes to preserve oxygen supply to metabolizing tissues during exposure to hypoxia.

O objetivo deste trabalho foi descrever o efeito da hipoxia no fluxo iônico corporal e nos parâmetros hematológicos em duas espécies de teleósteos da Amazônia: Serrasalmus eigenmanni e Metynnis hypsauchen. O aumento dos efluxos de Na+ e Cl- em M. hypsauchen expostos à hipoxia pode estar relacionado ao aumento da ventilação branquial e da eficiência da área da superfície respiratória, a fim de evitar redução na captação de oxigênio; e/ou com a diminuição do pHe, que pode inibir os transportadores de Na+ e Cl- e, então, reduzir o influxo destes íons. Os efluxos de Na+ e Cl- foram menores em hipoxia do que em normoxia para a espécie S. eigenmanni, possivelmente porque esta espécie em hipoxia poderia reduzir a ventilação branquial e a captação de oxigênio, a qual levaria a uma diminuição do efluxo branquial de íons e, conseqüentemente, à redução da perda de íons. O aumento do hematócrito (Ht) durante hipoxia em M. hypsauchen provavelmente foi causado pelo aumento do volume das células vermelhas do sangue (MCV). Para a espécie S. eigenmanni, o aumento da glicose possivelmente foi resultado do uso da mobilização da reserva de glicose. A espécie Metynnis hypsauchen mostrou ser mais sensível à hipoxia do que a espécie Serrasalmus eigenmanni, uma vez que a primeira espécie apresentou mais alterações significativas em seus parâmetros osmorregulatórios e hematológicos. Contudo, as alterações observadas em ambas as espécies são estratégias adotadas pelos peixes a fim de preservar o suprimento de oxigênio para metabolização nos tecidos durante exposição à hipoxia.

Further analysis of open-respirometry systems: an a-compartmental mechanistic approach

A system is said to be "instantaneous" when for a given constant input an equilibrium output is obtained after a while. In the meantime, the output is changing from its initial value towards the equilibrium one. This is the transient period of the system and transients are important features of open-respirometry systems. During transients, one cannot compute the input amplitude directly from the output. The existing models (e.g., first or second order dynamics) cannot account for many of the features observed in real open-respirometry systems, such as time lag. Also, these models do not explain what should be expected when a system is speeded up or slowed down. The purpose of the present study was to develop a mechanistic approach to the dynamics of open-respirometry systems, employing basic thermodynamic concepts. It is demonstrated that all the main relevant features of the output dynamics are due to and can be adequately explained by a distribution of apparent velocities within the set of molecules travelling along the system. The importance of the rate at which the molecules leave the sensor is explored for the first time. The study approaches the difference in calibrating a system with a continuous input and with a "unit impulse": the former truly reveals the dynamics of the system while the latter represents the first derivative (in time) of the former and, thus, cannot adequately be employed in the apparent time-constant determination. Also, we demonstrate why the apparent order of the output changes with volume or flow

Physiological constraints in the aerobic performance of hummingbirds

Hovering flight has been described as the most energetically expensive form of locomotion. Among the vertebrates, hummingbirds weighing only 1.5-20 g are the elite practitioners of this aerial art. Their flight muscles are, therefore, the most oxygen demanding locomotor muscles per unit tissue mass of all vertebrates. Tissue level functional and structural adaptations for oxygen transport are compared between hummingbirds and mammals in this paper. Hummingbirds present extreme structural adaptations in their flight muscles. Mitochondrial densities greater than 30 per cent are observed in their pectoral muscles, and the surface area of the inner membrane of their mitochondria is tvace that of mammals. This doubling of their mitochondrial oxidative capacity is accompanied by a proportional increase in the specific activity (per g tissue) of the mitochondrial manganese superoxide dismutase (SOD-Mn) in their flight muscles, thus indicating that oxygen toxicity is not a constraint in the aerobic performance of hummingbirds during hovering flight. Finally, the liver appears to play a major role in providing the necessary substrates for their high aerobic performance, and also in eliminating the oxygen free radicals formed during oxidative phosphorylation.

Relationship between oxygen consumption and body size of the amphinomid polychaete Eurythoe complanata

The oxygen consumption of young and adult specimens of the opolychaete Eurythoe complanata was determined in relation to body size. The equation Y=0.086 W 0.40, r2= 0.76 (P<0.01) was obtained from polychaetes with body sizes ranging from 0.15-4.74 g, at 20.0 ñ 1 gradfe C and 32 grade /00 salinity. The Q10 value (mean ñ SD) determined between 20.0 ñ 1 grade C and 28.4 ñ 1 grade C was 2.57 ñ 1.07. The metabolic rate obtained for E. complanata was lower than expected for an errant species, reflecting the more sedentary mode of life of the polychaete, and adaptation to an environment in which the animal may be expected to low oxygen availability