Flying insects: model systems in exercise physiology

Insect flight is the most energy-demanding exercise known. It requires very effective coupling of adenosine triphosphate (ATP) hydrolysis and regeneration in the working flight muscles.³¹P nuclear magnetic resonance (NMR) spectroscopy of locust flight muscle in vivo has shown that flight causes only a small decrease in the content of ATP, whereas the free concentrations of inorganic phosphate (P _i ), adenosine diphosphate (ADP) and adenosine monophosphate (AMP) were estimated to increase by about 3-, 5- and 27-fold, respectively. These metabolites are potent activators of glycogen phosphorylase and phosphofructokinase (PFK). Activation of glycolysis by AMP and P _i is reinforced synergistically by fructose 2,6-bisphosphate (F2,6P₂), a very potent activator of PFK. During prolonged flight locusts gradually change from using carbohydrate to lipids as their main fuel. This requires a decrease in glycolytic flux which is brought about, at least in part, by a marked decrease in the content of F2,6P₂ in flight muscle (by 80% within 15 min of flight). The synthesis of F2,6P₂ in flight muscle can be stimulated by the nervous system via the biogenic amine octopamine. Octopamine and F2,6P₂ seem to be part of a mechanism to control the rate of carbohydrate oxidation in flight muscle and thus function in the metabolic integration of insect flight.Dedicated to Dr. Ernst Zebe, Emeritus Professor of Zoology (University of Münster) on the occasion of his 70th birthday.     

Effect of taurine administration on liver lipids in guinea pig

Summary The oral administration of 0.4% taurine in drinking water for 14 consecutive days showed the following hepatic effects in male guinea pig. The percentage of tauro-conjugated biliary bile acids was increased from 17.2–54.2%; the ratio liver weight/body weight was increased, and fatty change was induced. Liver triglyceride concentration was accordingly increased; diglyceride and phosphatidylcholine concentrations were reduced by the treatment, while phosphatidylethanolamine level was not affected. These changes suggest an adverse effect of taurine administration on phosphatidylcholine hepatic synthesis.     

Anaerobic microbial conversion of three hydroxycinnamic acids

Summary Caffeic, ferulic and synapic acid are anaerobically degraded by a microbial consortium via the reduction of the double bond of the side chain, the replacement of the nuclear hydroxyl group in position 4 by hydrogen, the demolition of the side chain by the loss of a C₁ unit.     

Effects of methoprene and juvenile hormone on the oxidative metabolism of isolated mitochondria from flight muscle ofLocusta migratoria L.

Summary In vitro applications of juvenile hormone III and a juvenile hormone analogue, methoprene, were made to mitochondria isolated from dorsal longitudinal flight muscles of adultLocusta migratoria L. Both compounds completely inhibited oxygen consumption at the highest concentrations used. At lower concentrations, state 3 respiration and respiratory control were reduced but the ADP/O ratio was largely unaffected.     

The AA and ANA rat lines,selected for differences in voluntary alcohol consumption

Summary The offspring of rats that voluntarily select larger quantities of alcohol are heavier consumers of alcohol than the offspring of rats that tend to avoid it. Such selective breeding, repeated over many generations, was used to develop the AA (Alko, Alcohol) line of rats which prefer 10% alcohol to water, and the ANA (Alko, Non-Alcohol) line of rats which choose water to the virtual exclusion of alcohol. In addition to demonstrating the likely role of genetic factors in alcohol consumption, these lines have been used to find behavioral, metabolic, and neurochemical correlates of differential alcohol intake. Some of the line differences that have been found involve the reinforcing effects of ethanol, the changes in consumption produced by alcohol deprivation and nutritional factors, the behavioral and adrenal monoamine reactions to mild stress, the development of tolerance, the accumulation of acetaldehyde during ethanol metabolism, and the brain levels of serotonin. It is hoped that these studies will lead to a better understanding of the genetically-determined mechanisms that influence the selection of alcohol.     

Interaction of mitochondrial porin with cytosolic proteins

Summary Intracellular phosphorylation is an important step in active uptake and utilization of carbohydrates. For example glucose and glycerol enter the liver, cell along the extra intracellular gradient by facilitated diffusion through specific carriers and are concentrated inside the cell by phosphorylation via hexokinase or glycerol kinase. Depending on the function of the respective tissue the uptake of carbohydrates serves different metabolic purposes. In brain and kidney medulla cells which depend on carbohydrates, glucose and glycerol are taken up according to the energy demand. However, in tissues such as muscle which synthesize glycogen or like liver which additionally produce fat from glucose, the uptake of carbohydrates has to be regulated according to the availability of glucose and glycerol. How the reversible coupling of the kinases to the outer membrane pore and the mitochondrial ATP serves to fulfil these specific requirements will be explained as well as how this regulates the carbohydrate uptake in brain according to the activity of the oxidative phosphorylation and how this allows glucose uptake in liver, and muscle to persist in the presence of high glucose 6-phosphate without activating the rate of glycolysis.     

The physiology of the smooth muscle: an interdisciplinary review—part II

Summary In the guinea pig taenia coli, when glycogen is depleted by repeating Ca-induced contracture in excess K solution containing no glucose, the tension cannot be maintained. The decrease in tension is accompanied by reduction of high energy phosphate compounds and oxygen consumption. When substrate is readmitted to the glycogendepleted preparation in the presence of 2.4 mM Ca and 20 mM K, the first response is hyperpolarization of the membrane and relaxation, and this is followed by depolarization and development of contracture. The latter response is blocked by verapamil, suggesting that energy supply increases the Ca conductance of the plasma membrane. The early response is considered to be due to activation of electrogenic Ca pump, since this is not affected by ouabain as well as removal of Na and K. ATP produced by substrate readmission is probably preferentially utilized for Ca pump activation to reduce the intracellular. Ca. The recovery of tension is likely to be brought about by ATP supply not only to the contractile machinery but also to the plasma membrane to remove inactivation of Ca conductance. It is postulated that as the energy source is depleted, energy consumption is automatically limited by suppressing Ca influx, as a selfdefence mechanism. Since HB is as effective as glucose in the recovery of these processes, and also in the activation of electrogenic Na pump, the matabolic pathway of oxidative phosphorylation alone can support these functions without a contribution of the glycolytic pathway.     

Hepatic hydroxylation of melatonin in the rat is induced by phenobarbital and 7,12-dimethylbenzy[a]anthracene — implications for cancer etiology

The protective function of the pineal hormone melatonin in the etiology of cancer and carcinogenic activation is increasingly well-established. Low melatonin levels seem to parallel cancer growth. The question arises as to which factors cause the depression of melatonin levels and what the direct effects are. Melatonin is known to be metabolized in the liver by hydroxylation and subsequent conjugation yielding 6-sulfatoxymelatonin as a main product. Nevertheless, the microsomal monoxygenases catalyzing the first step have been poorly investigated. To further characterize these enzymes, typical inducers of three different sub-classes, namely phenobarbital, 7,12-dimethylbenz[a]anthracene, and 17-estradiol, were administered to female Fischer rats. Circadian urinary excretion patterns of melatonin and 6-sulfatoxymelatonin were determined over a 24-hour period on the third (second) day of induction. Liver homogenates were used to monitor the in vitro conversion of melatonin or 6-hydroxymelatonin to 6-sulfatoxymelatonin. Results of both approaches showed the microsomal monoxygenases catalyzing the 6-hydroxylation of melatonin to be strongly inducible by phenobarbital and to a lesser degree by the polyaromatic hydrocarbon 7,12-dimethylbenz[a]anthracene. The dramatic depletion of circulating melatonin as a result of these induction patterns and its possible implications for oncogenesis are discussed.     

Selection pressure drives the co-evolution of several lipid metabolism genes in mammals

Adipose tissue is an important endocrine organ and energy supplier.Its physiological effect on the regulation of the energy balance is considered an important factor underlying the evolution of mammals.To test whether the genes controlling lipid metabolism have undergone adaptive molecular change in the evolution of mammals,in this study,we used the orthologous gene sequences of 12 important lipid metabolism proteins (leptin,OB-RL,RXRA,RXRB,RXRG,PPARA,PPARB/D,PPARG,PNLIP,ADIPOQ,LPL and UCP1) from NCBI’s databases.We found evidence that 4 of the corresponding genes (leptin,ADIPOQ,PNLIP and PPARA) have undergone positive selection in their evolutionary history and that most adaptive changes occurred during the evolution of the super-clades Laurasiatheria (placentals) and suborders within Euarchontoglires (primates and rodents).Comparisons across sets of genes showed that in a third of cases,bursts of positive selection,more than would be expected by chance,occurred on corresponding branches.We propose that the positive selection drives adaptive changes in some lipid metabolism genes in or within Laurasiatheria and Euarchontoglires clades.Along with evidence from earlier studies,our results show that co-evolution among interacting lipid metabolism proteins has taken place.