Central administration of alpha-melanocyte-stimulating hormone changes lipid metabolism in chicks

Alpha-melanocyte-stimulating hormone (MSH) is well known as an anorexigenic peptide in the brain of mammals. In addition to this, brain alpha-MSH enhances heat production (HP), indicating that the peptide acts as a catabolic factor in the regulation of energy metabolism. The anorexigenic effect of alpha-MSH is also observed in chicks (Gallus gallus), but no information has been available for its effect on HP. The present study was performed to examine whether intracerebroventricular (ICV) injection of alpha-MSH increases HP in chicks. The injection of alpha-MSH (10 and 100 pmol) did not affect oxygen consumption, carbon dioxide production and HP during the 1 h post-injection period. This result was supported by another result that ICV injection of alpha-MSH did not affect locomotion activity in chicks. In contrast, the respiratory quotient was significantly lowered by the ICV injection of MSH. We also found that alpha-MSH significantly increased plasma non-esterified fatty acid concentrations. In summary, brain alpha-MSH appears to exert generally catabolic effects on lipid metabolism in the chick, but does not appear to be involved in the regulation of HP.     

Ontogeny of thermoregulation and energy metabolism in pygoscelid penguin chicks

The ontogeny of thermoregulation and energy metabolism of chinstrap (Pygoscelis antarctica) and gentoo (P. papua) penguins was studied on King George Island, South Shetland Island, Antarctica. The major findings of this study are: Chinstrap and gentoo penguin chicks hatched completely poikilothermic, due to their poor heat-production ability at low ambient temperatures. They were able to maintain high body temperatures and metabolic rates only by being brooded by adults. Newly hatched chinstrap penguin chicks had, at a specified ambient temperature, significantly higher metabolic rates than newly hatched gentoos. Moreover, chinstrap chicks maintained a significantly higher body temperature. It is suggested that this is a non-acclimatory metabolic adaptation of chinstrap penguin chicks to the lower mean temperatures of their breeding areas. On the 15th day after hatching, chinstrap chicks were completely, and gentoo chicks almost completely, homeothermic. In spite of their high thermogenic capacity from about day 10, chicks were not at that time capable of controlling heat dissipation, and were still dependent on their parents. In older downy chicks and fledglings, heat loss at low temperatures, expressed as heat conductance (CA), was similar to that found for the adults of other penguin species. Just before moulting the CA of chicks was lower than after moulting. Moulting alone did not cause a clear increase in CA. Towards the end of their stay on land the CA of pre-fledged gentoos decreased by 31%. This decrease was not connected with the development of feathers or growth in the chicks' weight. The combination of the low CA and high SMR of chicks gave very low lower critical temperatures, near -15 degrees C. The wide thermoneutral zones of the chicks covered the whole range of air temperature variations in the breeding colonies of both species studied on King George Island. The CA values of homeothermic chinstrap chicks were not lower than those of gentoos, despite the more southern breeding range of the former species. The older chicks of both species are well protected against cold. Any further increase in insulation in chinstrap chicks would be of no adaptative importance.     

Energy cost of whole-body protein synthesis measured in vivo in chicks

1. Energy cost of whole-body protein synthesis was measured in vivo in chicks by comparing the changes in protein synthesis and heat production after the administration of cycloheximide, an inhibitor of protein synthesis. 2. Incorporation of phenylalanine into whole-body protein fraction was promptly inhibited after the intravenous injection of cycloheximide, and the effect was sustained for at least 3 hr. 3. Both whole-body protein synthesis and total heat production were significantly reduced by the cycloheximide administration. 4. The energy cost of whole-body protein synthesis was calculated to be 5.35 kJ per g protein synthesis, and hence on a molar basis 7.52 ATPs are required per peptide bond synthesis.     

Studies on cerebral energy metabolism during the course of galactose neurotoxicity in chicks

—At various times during a 2-day study, the levels of adenine nucleotides and selected glycolytic intermediates were determined in brains of chicks fed a diet containing d -galactose (40%, w/w). The levels of ATP and glucose 6-phosphate had decreased by 9 h after initiation of the diet, whereas those of fructose 1,6-diphosphate, 3-phosphoglycerate, l -α-glycerophosphate, and lactate were not reduced until after 18 h had elasped. Although glucose 1-phosphate was not appreciably affected, glucose and glycogen were depleted during the latter stages of the toxicity. The cerebral levels of 3′,5′-cyclic AMP and citrate did not differ significantly between the two dietary groups at 48 h. The changes in the levels of cerebral glycolytic intermediates and high-energy phosphates during ischemia indicated that the glycolytic rate was diminished in the chicks fed galactose and that high-energy phosphate compounds were depleted sooner than in controls. After intraperitoneal injection of [¹⁴C]glucose, the specific radioactivity and levels of glucose in the plasma from chicks fed either diet were similar, whereas they were significantly reduced in the brains from galactosefed animals. We suggest that galactose interferes with the uptake of glucose into the brain and that this mechanism may be an important factor in d -galactose-induced neurotoxicity in the chick.     

Intracerebroventricular injection of glucagon-like peptide-1 changes lipid metabolism in chicks

Glucagon-like peptide-1 (GLP-1), derived from proglucagon, is thought to act as a negative regulator of energy homeostasis in mammals, since intracerebroventricular (ICV) injection of GLP-1 inhibits feeding behavior and enhances energy expenditure. The anorexigenic effect of GLP-1 is also observed in chicks, but whether brain GLP-1 enhances energy expenditure has not been investigated. The aim of the present study was to clarify the effect of ICV injection of GLP-1 on energy expenditure as well as metabolic changes in chicks. The injection of GLP-1 did not affect energy expenditure calculated from oxygen consumption and carbon dioxide production. On the other hand, the injection of GLP-1 significantly decreased respiratory quotient, suggesting that brain GLP-1 shifted the use of energy sources from carbohydrates to lipids. In support of this, ICV injection of GLP-1 increased plasma non-esterified fatty acid concentration while plasma glucose concentration was decreased. In conclusion, GLP-1 appears to act in the brain as a metabolic modulator rather than as a regulator of total energy expenditure in chicks.     

Energy metabolism inLeishmania

Alanine plays a key role in the response of promastigotes to osmotic stress and to hypoxia. It is rapidly released in response to hypo-osmolality, is consumed from its large intracellular pool under iso-osmotic conditions even in the presence of glucose, and is synthesized under hyperosmotic conditions even in the absence of glucose. Its rate of oxidation, in the presence or absence of any of ten other amino acids tested, is strongly inhibited by hyperosmolality. Glucose oxidation is also inhibited by hyperosmolality, but to a lesser extent than that of alanine, and is inhibited by alanine, glutamate, and aspartate. Hyperosmolality also inhibits the incorporation of label from [2-¹⁴C]acetate into the putative storage carbohydrate, mannan, which occurs via the glyoxylate bypass and the as yet unexplored mannoneogenic pathway. The rates of glycolysis and of oxidation of several amino acids decrease with increasing culture age, but the capacity to oxidize fatty acids increases, and in cells from 3-day stationary phase cultures hyperosmolality enhances rather than inhibits alanine oxidation.     

Energy metabolism in green cells

Background: Although fire is an important factor in determining cerrado vegetation, information about its effect on seed banks is sparse. Cerrado fires are rapidly moving surface fires with low residence time, producing only short-term heating of the uppermost centimetres of the soil. However, the reduction in vegetation cover and deposition of ashes increases the daily amplitude of soil temperature by as much as 35 °C.

Aims: To assess the effect of post-fire daily soil temperatures on the germination of one alien and nine native grasses.

Methods: Seeds were stored at alternating temperatures of 45 ºC/10 ºC (10 h/14 h) for 7 d or 30 d, simulating two different storage times in the soil seed bank before the onset of the rainy season. Germination was monitored over 30 d.

Results: The variation in temperature had a significant effect on the rate of seed germination in some species, either enhancing it (Aristida setifolia) or reducing it (Schizachyrium sanguineum). Increased storage time reduced the viability of S. sanguineum and Echinolaena inflexa. The invasive Melinis minutiflora had the highest germination rate and it also showed the best toleration of post-fire conditions (45 ºC/10 ºC) after 7 d, with significant reduction in the germination time after 30 d.

Conclusions: Fire seems to have a significant effect in the early life of cerrado grasses. Some native species responded positively to temperature oscillation, suggesting that they should be better prepared to compete with alien species after a fire, with more of their seeds germinating and/or at a more rapid rate.     

Energy metabolism in potoroine marsupials

Summary Fasting and fed metabolic rates were measured in three species of potoroine marsupials, the rufous rat-kangaroo (Aepyprymnus rufescens), the long-nosed potoroo (Potorous tridactylus) and the brush-tailed bettong (Bettongia penicillata). There were no significant differences among potoroine species in fasting metabolic rate. The lowest fasting heat production for each species was 11–20% less than the interspecific value of 295 kJ · kg^-0.75 · day^-1 for basal metabolism of mature, non-reproductive eutherian homeotherms. The respiratory quotient of all species was reduced significantly as starvation proceeded, but only for B. penicillata was there a significant effect of starvation duration on fasting heat production. The night-time activity of P. tridactylus and B. penicillata doubled their daytime fasting heat production; the corresponding increase for A. rufescens was only 25%. The calorimetric measurement of fed animals showed no differences in digestible energy or metabolisable energy between species. Nevertheless, P. tridactylus and B. penicillata produced more heat per unit metabolic body mass. The maintenance energy requirements (kJ · kg^-0.75 · day^-1) were 479, 494 and 345 for P. tridactylus, B. penicillata and A. rufescens, respectively. The net availability of metabolisable energy was about 0.70 in the three species. The combined heat production of fed female A. rufescens and their pouch young stayed relatively constant for the first two-thirds of pouch life, after which it rose sharply (20%) in response to the rapid growth of the young. Only during the last week of pouch life did the female enter negative energy balance. There was no indication that the metabolism of the female increased in response to the presence of a pouch young. The presence of pouch young did not alter the efficiency of utilisation of metabolisable energy. The daily energy requirement for maintenance was 0.83 MJ · day^-1 or 0.36 MJ · kg^-0.75 · day^-1.Abbreviations DM dry matter - EB energy balance - FHP fasting heat production - FMR fasting metabolic rate - HP heat production - ME metabolisable energy - MEI metabolisable energy intake - MHP maintenance heat production - NAME net availability of metabolisable energy - RQ respiratory quotient - STP standard temperature and pressure Present address: Laboratory of Biomedical and Environmental Sciences, University of California, Los Angeles, 900 Veteran Avenue, Los Angeles, CA 900024-1786, USA     

Energy metabolism in tumor cells

In early studies on energy metabolism of tumor cells, it was proposed that the enhanced glycolysis was induced by a decreased oxidative phosphorylation. Since then it has been indiscriminately applied to all types of tumor cells that the ATP supply is mainly or only provided by glycolysis, without an appropriate experimental evaluation. In this review, the different genetic and biochemical mechanisms by which tumor cells achieve an enhanced glycolytic flux are analyzed. Furthermore, the proposed mechanisms that arguably lead to a decreased oxidative phosphorylation in tumor cells are discussed. As the O(2) concentration in hypoxic regions of tumors seems not to be limiting for the functioning of oxidative phosphorylation, this pathway is re-evaluated regarding oxidizable substrate utilization and its contribution to ATP supply versus glycolysis. In the tumor cell lines where the oxidative metabolism prevails over the glycolytic metabolism for ATP supply, the flux control distribution of both pathways is described. The effect of glycolytic and mitochondrial drugs on tumor energy metabolism and cellular proliferation is described and discussed. Similarly, the energy metabolic changes associated with inherent and acquired resistance to radiotherapy and chemotherapy of tumor cells, and those determined by positron emission tomography, are revised. It is proposed that energy metabolism may be an alternative therapeutic target for both hypoxic (glycolytic) and oxidative tumors.     

Intracerebroventricular injection of neuropeptide Y modifies carbohydrate and lipid metabolism in chicks

The purpose of the present study was to investigate whether intracerebroventricular (ICV) injection of neuropeptide Y (NPY) affects heat production (HP), body temperature, and plasma concentrations of metabolic fuels in chicks. ICV injection of NPY (0, 188 or 375 pmol) did not affect HP, but significantly lowered respiratory quotient as well as the rectal temperature. These data suggest that the energy sources for HP were modified by NPY in the body. This idea was confirmed by subsequent experiments in which ICV injection of NPY significantly reduced plasma glucose and triacylglycerol concentrations but increased non-esterified fatty acid concentrations. The effect of NPY on the utilization of metabolic fuels was not associated changes in plasma catecholamine and corticosterone concentrations. In summary, the present study demonstrated that central NPY modifies peripheral carbohydrate and lipid metabolism in chicks.