Kinetics of homovanillic acid and determination of its production rate in the rhesus monkey.

Homovanillic acid (HVA) labelled with two deuterium atoms (d₂-HVA) was used to label the peripheral body pool of endogenous HVA (d₀-HVA). D₂-HVA was rapidly injected intravenously into Rhesus monkeys and concentrations of both d₂- and d₀-HVA in sequential samples of blood serum and urine determined by gas chromatography-mass spectrometry. Parameters describing the distribution and elimination of HVA, as well as its pool size, turnover, and synthesis rate were then calculated. Results indicate that the decline of serum d₂-HVA concentration with time is multiexponential, with a biological half-life ranging from 35.9 to 102 min in the four monkeys studied. The apparent volume of distribution of d₂-HVA in the body was 0.813–1.17 1/kg. Serum clearance was 7.28–18.2 ml/kg/min. For most animals, only about 50% of the administered dose of d₂-HVA was recovered unchanged in the urine. Renal clearance ranged from 3.79 to 17.0 ml/kg/min, and d₀-HVA excretion rates ranged from 19.5 to 64.1 μg/hr. The size of the peripheral body pool of HVA, calculated from serum kinetic parameters, was 63.3–80.7 μg; HVA turnover was 5.43–13.9 μg/1/hr; and HVA production rate was calculated to be 36.6–84.3 (5.23–12.6 μg/kg/hr).     

Effect of verapamil on glycogenolysis and gluconeogenesis in the perfused rat liver

In perfused livers from fed rats, rates of glucose production (glycogenolysis) were 133 +/- 12 mumol/g/hr. Infusion of 2 microM verapamil into these livers decreased the rates of glucose production significantly to 97 +/- 15 mumol/g/hr within 10 min. Conversely, rates of production of lactate plus pyruvate (glycolysis) of 64 +/- 6 mumol/g/hr were not significantly altered by verapamil (60 +/- 3 mumol/g/hr). When 50 microM verapamil was infused, however, rates of both glycogenolysis and glycolysis were diminished to 56 +/- 11 and 43 +/- 5 mumol/g/hr, respectively. In perfused livers from fasted rats, infusion of 20 mM fructose increased the rates of production of glucose (gluconeogenesis) significantly from 11 +/- 7 to 121 +/- 17 mumol/g/hr. These rates reached 138 +/- 7 mumol/g/hr upon the simultaneous infusion of verapamil (2 microM). In these livers, fructose also increased rates of production of lactate from 6 +/- 2 to 132 +/- 11 mumol/g/hr, which were further increased to 143 +/- 8 mumol/g/hr when 2 microM verapamil was infused. The results show that calcium-dependent processes involved in hepatic carbohydrate metabolism respond differently to the calcium channel blocker verapamil. Low concentrations of verapamil inhibited glycogenolysis significantly while having no effect on either glycolysis or gluconeogenesis. These data suggest that these two processes have different sensitivities to changes in intracellular calcium concentrations and/or different sources of regulatory calcium.     

Overwintering of European hedgehogs<Emphasis Type="Italic">Erinaceus europaeus</Emphasis> in a Danish rural area

Ten radio-tagged hedgehogsErinaceus europaeus (Linnaeus, 1758) were monitored during the winter of 2001/2002 in a Danish rural area. The study was aimed at measuring parameters essential for hibernation success and the fate of the mainly juvenile hedgehogs being recorded. The average duration of hibernation was found to be 179 days for juveniles (n=6) and 198 days for adult females (n=3). The most often used nesting habitat types were forested areas (55%). The hedgehogs typically used 2 nests during the hibernation period, but up to 4 different nests used by one hedgehog were found. Time spent in different nests varied considerably (6-187 days). The average weight loss during hibernation was 22.1% for juveniles and 30.2% for adult females. Minimum body mass sufficient for survival was registered to be 513 g prior to hibernation. Nine of the hedgehogs survived until departure from their hibernacula, while the fate of 1 juvenile is unknown. Indication was thus found that the minimum weight required to survive the winter has previously been overestimated.     

Seasonal variation of cardiovascular function in the marmot, Marmota flaviventris

Monthly measurements of heart rate, mean arterial pressure, and cardiac output were made on active and hibernating marmots from the time of emergence from hibernation through the next hibernation period. From these measurements cardiac index, stroke index, and total peripheral resistance were calculated on the basis of estimated lean body mass. Heart rate was low after emergence (132 +/- 9.5 beats (B)/min), peaked in August (160 +/- 9.3 B/min), and then fell slightly in September and October. During hibernation heart rate fell to 9 +/- 1.1 B/min. Mean arterial pressure, which was low in early spring (101 +/- 6.9 mm Hg), rose to a peak value in June (131 +/- 7.7 mm Hg) and remained essentially unchanged until hibernation when it fell to 52 +/- 4.0 mm Hg. Cardiac index (61 +/- 4.9 ml/kg min) in March rose to a peak in May (83 +/- 8.5 ml/kg min) and fell linearly until October. There was an additional drop in cardiac index during hibernation (7.6 +/- 0.9 ml/kg min). Total peripheral resistance increased linearly from the time of emergence until October. Most of this change was due to the decrease in cardiac index. Stroke index showed no significant changes in the prehibernation period, but increased by 55% during hibernation. Maintenance of arterial pressure in the months preceding hibernation in the face of diminishing cardiac index indicate that alterations in vasomotor tone or shifts in patterns of blood flow occurred prior to the hibernation period.     

Relationship Between Energy Substrate Utilization and Specific Growth Rate in Aspergillus nidulans

The maintenance coefficient of glucose-limited Aspergillus nidulans chemostat cultures at 30 C was 0.018 g per g (dry weight) per hr for glucose and 0.55 mmoles per g (dry weight) per hr for oxygen. These values can only be approximate because melanin was produced by the mold at low growth rates and because it is unlikely that this polymer contributed to the maintenance energy requirement although it contributed to the dry weight. Biomass (defined here as dry weight minus melanin) was used to calculate a more meaningful maintenance coefficient for glucose (0.029 g of glucose per g of biomass per hr). At the highest growth rates examined, a nonlinear relationship between growth rate and glucose utilization rate was obtained, suggesting a qualitative change in the metabolic activities of the mold at high growth rates. The oxidative capacity of the mold was highest at the highest growth rates. This observation indicates that the increased substrate utilization rate observed at the higher growth rates is a reflection of enhanced enzyme synthesis. This hypothesis was verified by assaying the specific activities of several enzymes at different growth rates. However, in contrast to all the other enzymes assayed, the activities of reduced nicotinamide adenine dinucleotide phosphate: (acceptor) oxido-reductases were highest at the lowest growth rates.     

Timing of ovulation and early embryonic development in Myotis lucifugus (Chiroptera: Vespertilionidae) from northern central Ontario

Female Myotis lucifugus lucifugus, obtained from a hibernaculum in northern central Ontario, were aroused during the week that normal departures from hibernation began, maintained in large cages at 28-30 degrees C, and fed mealworms daily. Some bats ovulated less than 24 hr after arousal, and with one exception, all bats with normal, mature follicles ovulated within 72 hr. Histological examination of reproductive tracts from ovulated bats indicated that oviductal transit was completed in 24-48 hr, and that blastocyst formation and implantation occurred 4 and 10 days, respectively, after fertilization. These time intervals were somewhat shorter than those reported in previous studies; however, the differences appeared to be due to the relative accuracy in determining the time of ovulation, not to differences in rates of development among different populations.     

Body temperature patterns before, during, and after semi-natural hibernation in the European ground squirrel

Ground squirrels undergo extreme body temperature fluctuations during hibernation. The effect of low body temperatures on the mammalian circadian system is still under debate. Using implanted temperature loggers, we recorded body temperature patterns in European ground squirrels kept in an enclosure under natural conditions. Although hibernation onset was delayed, hibernation end corresponded closely to that measured in a field population. Circadian body temperature fluctuations were not detected during deep torpor, but indications of circadian timing of arousal episodes at higher temperatures were found at the beginning and end of hibernation. One male exhibited synchronised arousals to a relatively constant phase of the day throughout hibernation. All animals first entered torpor in the afternoon. Daily body temperature fluctuations were decreased or distorted during the first days after hibernation. We hypothesise that hibernation may affect the circadian system by either decreasing the expression of the circadian oscillator, or by decreasing the amplitude of the circadian oscillator itself. possibly due to gradual, temperature dependent, internal desynchronisation. The latter mechanism may be beneficial because it might facilitate post-hibernation re-entrainment rates.     

Studies on gluconeogenesis and protein synthesis in isolated hepatocytes.

Glucose production was studied in isolated hepatocytes using various substrates and with increasing substrate concentrations (0-10 mM). Fructose was the best gluconeogenic substrate while other substrates studied stimulated net glucose production in the following decreasing order: lactate, pyruvate, glycerol, galactose, alanine, and succinate. Studies on oxygen consumption showed that endogenous respiration was linear for 60 min and was not altered by extracellular calcium. Studies on the incorporation of 14C-leucine into protein was linear for only 3-4 hr in cells containing low glycogen. However, cells containing high glycogen incorporated 14C-leucine into protein linearly for 8-10 hr. About 3 mg of protein per g per hr was synthesized by isolated cells when incubated for 4 hr with amino acids mixture, glucose, lactate, and insulin.     

Respiratory organs in wolf spiders: morphometric analysis of lungs and tracheae in Pardosa lugubris (L.) (Arachnida, Araneae, Lycosidae)

The respiratory system of the wolf spider Pardosa lugubris consists of a pair of well-developed lungs and four unbranched tube tracheae. We used stereological morphometric methods to investigate the morphological diffusing capacity of the lungs and of the walls of the tracheae ('lateral diffusing capacity'). We examined three groups of female P. lugubris with different mean body masses. The barrier thickness of the gas-exchange epithelium of the lungs was 0.17 microm for the total diffusion barrier and the calculated oxygen diffusing capacity (D(O2)) for the lungs was between 12.9 and 13.4 microl min(-1)g(-1)kPa(-1). Measured metabolic rates compared with the D(O2) of the lungs result in necessary oxygen partial pressure differences of 0.2 kPa during rest and 2.1 kPa during maximum measured activity. The diffusion barrier of the entire tracheal walls was 0.31-0.50 microm and the calculated lateral D(O2) was 0.05-0.2 microl min(-1)g(-1)kPa(-1). Therefore, tracheae are of no importance for the overall oxygen exchange. However, they might be of some importance in local oxygen supply or in overall carbon dioxide release. The comparison with the respiratory system of the jumping spider Salticus scenicus reveals that the lungs have very similar mass-specific D(O2) in both species, and that, in addition, jumping spiders possess a much better developed tracheal system.     

Metabolic rate of feeding and fasting juvenile midland painted turtles, Chrysemys picta marginata

1. Resting metabolic rates at 25 degrees C were determined for juvenile midland painted turtles that had recently been fed or fasted for 1, 2, 4, 6, 10, 14 or 19 days. 2. Recently fed turtles had an oxygen consumption rate of 211 microliter O2/g/hr. This decreased by 32% on the first day of the fast and by 69% by the 19th day. 3. Mass of the turtles (4.91-14.30 g) did not affect the rate of oxygen consumption (VO2).     

The development of homeothermy in mink (Mustela vison)

In mink (Mustela vison) kits newborn mortality is very high. One of the major causes of death is hypothermia. The objectives of this study were to observe the development of thermoregulation in mink kits, and their ability to maintain their body temperature during the postnatal period (1-50 days of age). Based on the kit's body weight (BW), and rectal and ambient temperature measurements during cold (+4 degrees C) and warm (+40 degrees C) exposures, a homeothermy index (HI) and cooling and warming rates were calculated. No significant differences in the body temperatures were found between the kits and the dam after 36 days of age. The kits were able to maintain homeothermy by 22 days of age (HI 90%). The body cooling rate was 0.88+/-0.04 degrees C min(-1) on day 1 but only 0.35+/-0.03 degrees C min(-1) at 22 days of age. The body WR was lower: day 1, 0.85+/-0.04 degrees C min(-1) and 0.22+/-0.03 degrees C min(-1) at 22 days of age. All measured and calculated thermophysiological variables were significantly influenced by BW and age of the kit.     

Development of homeothermy in the diving petrels Pelecanoides urinatrix exsul and P. georgicus, and the Antarctic prion Pachyptila desolata

Body temperatures of South Georgia diving petrel (P. georgicus) chicks increased from about 37.5 degrees C at hatching to between 38.5 and 39 degrees C within two weeks. Temperatures of common diving petrel P. u. exsul chicks averaged 38.8 degrees C after two weeks of age. Burrow temperatures varied between 5 and 10 degrees C. Measurements of oxygen consumption and body temperature indicated that chicks achieve effective endothermy at 5 degrees C after 9 days in P. u. exsul, 5-6 days in P. georgicus, and 0 days in the Antarctic prion (Pachyptila desolata). The maximum mass-specific, cold-induced oxygen consumption of small chicks that we could measure with our apparatus (ca. 5-6 cc O2/g per hr) was achieved at 5-6 days in P. u. exsul, 3 days in P. georgicus, and 0 days in P. desolata. Mass-specific thermal conductance decreased with age and body size in all 3 species, but was highest in P. u. exsul and lowest in P. desolata. Conductance was similar at the age of effective endothermy in all 3 species (ca. 3 J/g per hr per degrees C). The period required for the development of endothermy is related to age-specific changes in both conductance and capacity for heat production and it closely parallels the length of the brooding period. It is suggested that the length of the period of thermal dependence of the chick is related to the distance between feeding areas and the nesting site.     

Gas Consumption and Growth Rate of Hydrogenomonas eutropha in Continuous Culture

The bacterium Hydrogenomonas eutropha is under consideration for use in a regenerative life-support system for manned space missions of long duration. A 4-liter continuous culture unit containing the organism was operated for a period of 272 days under autotrophic environmental conditions. The best steady-state run achieved with this unit was observed over a 22-day time interval after 181 days of operation. During this time, the culture consumed an average of 22.9 +/- 2.0 ml of carbon dioxide per min, 38.1 +/- 3.3 ml of oxygen per min, and 128.5 +/- 10.6 ml of hydrogen per min. It required 18.7 +/- 1.2 liters of fresh nutrient medium per 24 hr to maintain a constant, preestablished cell population of 1.65 g (dry weight) per liter. The ratio of consumption of carbon dioxide, oxygen, and hydrogen varied from 1:1.2:4.5 to 1:1.9:6.6, with an average of 1:1.7:5.7. Based on these values, approximately 60 liters of the culture would be necessary to balance the gas exchange of one man.     

Hibernation patterns and energy expenditure in hedgehogs from semi-arid and temperate habitats

Summary Hibernation patterns, body temperature (T _b) and oxygen consumption ( ) were measured during hibernation in two hedgehog species, a desert speciesHemiechinus auritus (body mass 367 g) and a temperate habitat speciesErinaceus europaeus (body mass 598 g). A continuous ambient temperature of 11 °C was the only necessary condition for both species to enter hibernation outdoors and in the laboratory. At this temperature, hibernation could be induced at any time of the year. Hibernation bouts ofHemiechinus were regular and short (average 4.8 days), whereas those ofErinaceus lasted 5 to 27 days (average 9.3 days). The frequency of spontaneous arousals was 5.3 and 2.9 per month forHemiechinus andErinaceus, respectively. None of the hedgehogs took any food during arousal periods. Both species had the sameT _b during hibernation (12.5 °C) and during arousal (33 °C). of the hibernatingHemiechinus was twice the rate ofErinaceus (0.050 vs. 0.025 ml g^–1 h^–1), but during arousal it was the same for both. The monthly average energy expenditure for both species was 1,477 kJ per animal, which is 15% of the energy used by non-hibernating hedgehogs. The corresponding amount of fat catabolized was 37 g per month. This mass loss would limit the hibernation inHemiechinus to 3.9 months and inErinaceus to 6.5 months. Although hibernation inHemiechinus does not constitute a special adaptation to hot environments, it significantly improves the hedgehog's energy economy during the desert winter.     

Lactate uptake by the fetal sheep liver

Lactate is produced by the sheep placenta and is an important metabolic substrate for fetal sheep. However, lactate uptake and release by the fetal liver have not been assessed directly. We measured lactate flux across the liver in 16 fetal sheep at 129 (120-138) days gestation that had catheters chronically maintained in the fetal descending aorta, inferior vena cava, right or left hepatic vein, and umbilical vein. Lactate and hemoglobin concentrations and oxygen saturation were measured in blood drawn from all vessels. Umbilical venous, portal venous, and hepatic blood flow were measured by injecting radionuclide-labeled microspheres into the umbilical vein while obtaining a reference sample from the descending aorta. We found net hepatic uptake of lactate (5.0 +/- 4.4 mg/min per 100 g liver). A large quantity of lactate was delivered to the liver (94.2 +/- 78.1 mg/min per 100 g), so that the hepatic extraction of lactate was only 7.7 +/- 6.5%. Hepatic oxygen consumption was 3.18 +/- 3.3 ml/min per 100 g, and the hepatic lactate/oxygen quotient was 2.07 +/- 1.54. There was no significant correlation between hepatic lactate uptake and hepatic lactate or glucose delivery, hepatic oxygen consumption, hepatic blood flow, hepatic glucose flux, total body oxygen consumption, arterial pH, oxygen content, or oxygen saturation. There was, however, a significant correlation between hepatic lactate uptake and umbilical lactate uptake (r = 0.74, P less than 0.005) such that net hepatic lactate uptake was nearly equivalent to that produced across the umbilical-placental circulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Heart-type fatty acid-binding protein reciprocally regulates glucose and fatty acid utilization during exercise

The role of heart-type cytosolic fatty acid-binding protein (H-FABP) in mediating whole body and muscle-specific long-chain fatty acid (LCFA) and glucose utilization was examined using exercise as a phenotyping tool. Catheters were chronically implanted in a carotid artery and jugular vein of wild-type (WT, n = 8), heterozygous (H-FABP(+/-), n = 8), and null (H-FABP(-/-), n = 7) chow-fed C57BL/6J mice, and mice were allowed to recover for 7 days. After a 5-h fast, conscious, unrestrained mice were studied during 30 min of treadmill exercise (0.6 mph). A bolus of [(125)I]-15-(p-iodophenyl)-3-R,S-methylpentadecanoic acid and 2-deoxy-[(3)H]glucose was administered to obtain rates of whole body metabolic clearance (MCR) and indexes of muscle LCFA (R(f)) and glucose (R(g)) utilization. Fasting, nonesterified fatty acids (mM) were elevated in H-FABP(-/-) mice (2.2 +/- 0.9 vs. 1.3 +/- 0.1 and 1.3 +/- 0.2 for WT and H-FABP(+/-)). During exercise, blood glucose (mM) increased in WT (11.7 +/- 0.8) and H-FABP(+/-) (12.6 +/- 0.9) mice, whereas H-FABP(-/-) mice developed overt hypoglycemia (4.8 +/- 0.8). Examination of tissue-specific and whole body glucose and LCFA utilization demonstrated a dependency on H-FABP with exercise in all tissues examined. Reductions in H-FABP led to decreasing exercise-stimulated R(f) and increasing R(g) with the most pronounced effects in heart and soleus muscle. Similar results were seen for MCR with decreasing LCFA and increasing glucose clearance with declining levels of H-FABP. These results show that, in vivo, H-FABP has reciprocal effects on glucose and LCFA utilization and whole body fuel homeostasis when metabolic demands are elevated by exercise.     

The relationship between rate of oxygen consumption, heart rate and thermal conductance of the dik-dik antelope (Rhynchotragus kirkii) at various ambient temperatures

1. The extent of cardiovascular adjustments to heat and cold were investigated between ambient temperatures of 5 and 45 degrees C by measuring conductance and the rates of oxygen consumption and heart beats. 2. Minimum heart rate was observed at 25 degrees C (114 +/- 9 beats/min). In the heat at 45 degrees C heart rate was observed to increase only slightly (127 +/- 12 beats/min) but in the cold -5 degrees C heart rate nearly doubled that at 25 degrees C. 3. Thermal conductance was on average 0.031 mlO2 (g. hr. degrees C)-1 below 25 degrees C but increased by more than 20 times at 40 degrees C. 4. A positive correlation between heart rate and rate of oxygen consumption was demonstrated below 25 degrees C and the relation may be of practical use.     

Effects of changing ambient temperature on metabolic, heart, and ventilation rates during steady state hibernation in golden-mantled ground squirrels (Spermophilus lateralis)

To determine whether metabolic rate is suppressed in a temperature-independent fashion in the golden-mantled ground squirrel during steady state hibernation, we measured body temperature and metabolic rate in ground squirrels during hibernation at different T(a)'s. In addition, we attempted to determine whether heart rate, ventilation rate, and breathing patterns changed as a function of body temperature or metabolic rate. We found that metabolic rate changed with T(a) as it was raised from 5 degrees to 14 degrees C, which supports the theory that different species sustain falls in metabolic rate during hibernation in different ways. Heart rate and breathing pattern also changed with changing T(a), while breathing frequency did not. That the total breathing frequency did not correlate closely with oxygen consumption or body temperature, while the breathing pattern did, raises important questions regarding the mechanisms controlling ventilation during hibernation.     

Glucocorticoids and hypothermic induction and survival in the rat

Glucocorticoids (GC) are important for thermoregulatory responses to low environmental temperatures. Pretreatment of hamsters, which are capable of natural hibernation, with cortisone acetate has been demonstrated to improve carbohydrate homeostasis during hypothermia. The objectives of the current studies were to evaluate the effects of GC pretreatment of a nonhibernator, the rat, on (i) cooling time, (ii) carbohydrate homeostasis (in terms of liver and cardiac glycogen concentrations and plasma glucose concentration), and (iii) duration of survival in hypothermia. In addition, the effects of liver glycogen depletion on cooling times and survival were examined. Hypothermia was induced in rats by exposure to a helium:oxygen (80:20, Helox) atmosphere at 0 degree C. Pretreatment of rats with triamcinolone acetonide (1.5 mg/kg/day, sc, 48, 24, and 1 hr prior to induction) significantly (P less than 0.05) lengthened induction time, while fasting was associated with a significant decrement (25%). While liver and cardiac glycogen levels in control and GC-treated rats fell approximately 45% during cooling, this reduction occurred over a significantly greater period of time in treated rats and suggests a sparing of glycogen or increased capacity for its production in response to GC. Glycogen utilization was accompanied by a hyperglycemia in control, GC-treated, and fasted groups. Survival in hypothermia at a rectal temperature of 14-15 degrees C in GC-treated (9.5 +/- 1.2 hr) and fasted (10.9 +/- 0.9 hr) rats was not significantly different from control (10.5 +/- 1.1 hr) values. These findings suggest that treatment with GC can increase the thermogenic capacity of the rat (as evidenced by an increased induction time) and promote carbohydrate homeostasis, but does not contribute to an enhancement of survival in the hypothermic nonhibernator.