Comparative Biochemistry and Physiology Part A: Physiology最新文献

Overall similarities among all genera and 18 of 20 species of icefishes, family Channichthyidae, were determined based on data of the composition of axial metameric structures (unpaired fins and vertebral column). The results of a cluster analysis are compared with some traditional ideas and the cladistic phylogenetic hypothesis about the interrelationships of icefishes.

We measured metabolic rates of adult male Drosophila melanogaster allowed to evolve in the laboratory at 18 and 25°C and compared these with measurements of metabolic rates of flies collected along a latitudinal gradient in Australia. Metabolic rates of flies that had evolved in the laboratory at low temperature were 5–7% higher than those of flies allowed to evolve at high temperature. Metabolic rates of field collected increased with latitude when measured at 18°C but not at higher temperature (25°C) and were about 9% greater in high latitude (∼41′00) flies than low latitude (16′53) flies. Metabolic rate was strongly influenced by measurement temperature; estimated Q₁₀s ranged from 1.79 to 2.5 for measurements made at 18 and 25°C. Metabolic rate scaled isometrically with body mass; the estimated slope of a ln-ln regression of metabolic rate and body mass was 1.03 ± 0.1. We used our measures of metabolic rate and activity to estimate the minimum cost of transport (MCOT) while walking. The estimates of MCOT have high standard errors (lab, 34.30 ± 14.2 ml O₂/g/km; and field, 38.0 ± 17.0 ml O₂/g/km); however, they differ by only 3–9% from predicted values based on allometric relationships reported in the literature.

Glucose-6-phosphate dehydrogenase (G6PD) and l-glutamate dehydrogenase (GDH) from Antarctic fish were isolated and characterized. G6PD was purified from the erythrocytes of red-blooded Dissostichus mawsoni and from the colorless blood of the icefish Chionodraco hamatus. Structural and functional characterization showed that the two enzymes do not differ significantly from each other. GDH was purified from the liver of the icefish Chaenocephalus aceratus. As in other fish GDHs, it showed a marked preference for NAD⁺. The amino acid sequence of the active-site peptide is virtually identical to that of other fish and vertebrate counterparts. Although the basic structural features of the Antarctic enzymes are similar to those of mesophilic organisms, some catalytic and thermodynamic properties make the Antarctic enzymes more suited to cold-adapted organisms.

Mammalian hibernation requires specific regulatory controls on metabolism to coordinate entry, maintenance, and arousal stages, as well as adjustments to many metabolic functions to support long-term dormancy. Several mechanisms of metabolic regulation are involved in potentiating survival. One of these is the reversible phosphorylation of regulatory enzymes, including glycogen phosphorylase, phosphofructokinase, pyruvate kinase, and pyruvate dehydrogenase. In particular, the sharp suppression of pyruvate dehydrogenase during hibernation shows the importance of control over mitochondrial oxidative metabolism for reducing metabolic rate. Fine control over specific enzymes also occurs via differential temperature effects on kinetic and allosteric properties. Analysis of temperature effects on the properties of pyruvate kinase, fructose-1,6-bisphosphatase, creatine kinase, and citrate synthase from ground squirrel or bat tissues shows a range of responses, some that would reduce enzyme activity in the hibernating state and some that would promote temperature-insensitive enzyme function. Reduced tissue phosphagen and adenylate levels, but not energy charge, may also contribute to overall metabolic suppression. New research is exploring the role of transcriptional and translational controls in hibernation via several approaches. For example, immunoblotting with antibodies to heat shock proteins (hsp 70 family) revealed the presence of constitutive hsc 70 in bat tissues but levels of the protein did not change between euthermic and hibernating states and neither the inducible hsp 70 nor the glucose-responsive protein grp 78 appeared during hibernation.

A survey of the literary evidence on cryogens and hibernation induction triggers is given and the results of experiments on the effect of hypothalamic or i.v. injections of opioids and plasma from hibernating European hamsters on body temperature control of rabbits are presented.

Pharmacological doses of a delta opioid—DADLE (25 or 50 μg), when injected into the anterior hypothalamus, induce a small and short-lasting hypothermic effect in cold exposed rabbits, due to the downward shift of the temperature threshold for shivering. Lower doses (5 μg) are without effect, similarly as i.v. administrations (500 μg/kg) of this substance. Intrahypothalamic injections of met-enkephalin (0.1–1 μg) induce a slight hyperthermia due to the shift of all thermoregulatory effectors to higher body temperatures. Intrahypothalamic injections of plasma from hibernating European hamsters do not influence the body temperature control in rabbits.

The biochemical composition (expressed as % dry weight) of the test, gut and gonad of Paracentrotus lividus was estimated. Sea urchin biochemical composition was studied in two natural populations of a coastal Mediterranean lagoon and in two rearing stations, one in open sea and one inland. Artificials feeds were administered to the reared urchins in order to evaluate variations in the biochemical composition of this species when provided different food resources. The results reveal that, for the natural populations examined in this study, the biochemical composition of the gonad, gut, and test do not depend on food availability and, hence on the quantity of food consumed. The comparison between wild and reared sea urchin biochemistry reveals that organ biochemical composition is strongly influenced by the quality of the feed. The use of artificial feed containing fish meal (rich in protein), favours a storage of reserves in the gonad, the gut, and even in the test in the form of lipids and/or carbohydrates. This is true for both open sea and inland rearing.

Mature pelagic forage fish species (capelin, sand lance, squid) had greater lipid concentrations than juvenile age-classes of large demersal and pelagic fish species (walleye pollock, Pacific cod, Atka mackerel, greenling, prowfish, rockfish, sablefish). Myctophids preyed on by puffins have at least twice as much lipid per gram compared to mature capelin, sand lance and squid, and an order of magnitude greater lipid concentrations than juvenile forage fish. Energy density of forage fishes was positively correlated with lipid content, and negatively correlated with water, ash-free lean dry mass (mostly protein), and ash contents.

We investigated the abilities of sparrows, Zonotrichia leucophrys, to adjust their rates of oxidation of endogenously derived essential amino acids and to retain these indicator amino acids (IAA) in tissue proteins in response to either a dietary deficiency of total protein, threonine or sulfur amino acids (SAA). Tissue proteins of birds were uniformly labeled with either 1-¹⁴C-phe or 1-¹⁴C-val by injecting birds IM with a tracer dose of labeled amino acid 21 days before dietary treatments began. Oxidation rates and retention of IAA in tissue proteins were compared between well-nourished birds and those fed deficient diets during two phases of their annual cycle, molt and winter maintenance. Non-molting birds fed diets low in protein or in threonine and molting birds fed diets low in protein reduced oxidation rates and increased retention of IAA after 9 days of dietary treatment as compared with well-nourished birds. In contrast, non-molting birds fed diets low in SAA showed no adjustments in oxidation or retention of IAA and molting birds fed diets low in SAA showed increased rates of oxidation and lower retention of IAA as compared with well-nourished control birds. In those birds able to adjust to dietary deficiencies, decreased oxidation and increased retention rates closely approximated earlier reported decreases in muscle protein degradation rates in response to malnutrition. Reduced protein degradation rates may be the preeminent compensatory mechanism in protein sparing during malnutrition, whereas adjustment in oxidation and reutilization of endogenously derived amino acids seems to play only a small role. Differing responses of birds to SAA deficiency as compared with protein or threonine deficiency probably result from depletion of glutathione pools and a resulting disturbance to the normal economy of protein metabolism.

Between 1992 and 1994, temperature effects on cardiac pacemakers of three notothenioid fish species were investigated at Scott Base and Terra Nova Bay Station, Antarctica by recording electrical activity from isolated atria. Spontaneous rhythmic electrical activity correlated closely with visible contractions of the atrium. For the icefish Chionodraco hamatus, a mean rate of 15.2 ± 0.69 beats per minute (B/min) was recorded at 0°C, which agreed well with a mean pressure pulse frequency of 15.3 ± 0.42 B/min determined in vivo with a caudal arterial cannula. At the same temperature, slightly higher intrinsic rates of 23.5 ± 0.42 and 24.26 ± 0.88 B/min were measured in the red-blooded nototheniids Trematomus bernacchii and Pagothenia borchgrevinki, respectively. A bimodal distribution of rates was apparent in deteriorating preparations and fatigued low-frequency subpopulations were eliminated from further analysis. Linear regression confirmed that the atrial pacemaker is slower in C. hamatus but that temperature coefficients are similar for all 3 species: C. hamatus, f_H = 16.39 + 2.89 T; T. bernacchii, f_H = 24.55 + 2.69 T; P. borchgrevinki, f_H = 24.78 + 3.25 T, where f_H = heart rate, B/min and T = temperature, °C. The results appear to have predictive value for other antarctic fishes.