Search results for "Adenine nucleotide"

Flying insects: model systems in exercise physiology

1996

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 synergistica…

Control of adenine nucleotide metabolism and glycolysis in vertebrate skeletal muscle during exercise.

1996

The turnover of adenosine triphosphate (ATP) in vertebrate skeletal muscle can increase more than a hundredfold during high-intensity exercise, while the content of ATP in muscle may remain virtually unchanged. This requires that the rates of ATP hydrolysis and ATP synthesis are exactly balanced despite large fluctuations in reaction rates. ATP is regenerated initially at the expense of phosphocreatine (PCr) and then mainly through glycolysis from muscle glycogen. The increased ATP turnover in contracting muscle will cause an increase in the contents of adenosine diphosphate (ADP), adenosine monophosphate (AMP) and inorganic phosphate (P(i)), metabolites that are substrates and activators o…

Pharmacological analysis of intrinsic neural control of rat duodenum motility in vitro

1988

Biokinetisches Verhalten und Stoffwechselwirkungen von Fructose bei hochdosierter Dauerinfusion an der Ratte

1976

The steady-state blood level of fructose during 24 hours intravenous infusion in response to different doses follows saturation kinetics. Even after toxic doses of 1.5 g/kg/h no depletion of liver adenine nucleotides can be observed after 24 hours. In the kidneys, however, ATP, ADP and total adenine nucleotides were decreased after a dose of 1.5 g/kg/h of fructose. The blood glucose increased continuously at infusion rates of 1.5 g/kg/h. Inorganic phosphate in the blood increased at doses of 1.0 and 1.5 g/kg/h. The weight of the kidneys increased, presumably through water uptake. Urinary secretion was drastically reduced at doses above 1.0 g/kg/h. An appreciable activity of ketohexokinase c…

Involvement of purinergic nerves in the NANC inhibitory junction potentials in pigeon oesophageal smooth muscle.

2004

1. Electrical field stimulation (EFS) (0.5 ms in train of 2-32 Hz for 300 ms) in smooth muscle of pigeon oesophagus, in the presence of atropine (1 microm) and guanethidine (1 microm), elicited an inhibitory response consisting of a transient hyperpolarization (inhibitory junction potential, IJP) associated with muscle relaxation. 2. Sodium nitroprusside (SNP, 100 microm) induced hyperpolarization correlated to mechanical relaxation. 3. The nitric oxide (NO) synthase inhibitor N(omega)-nitro-l-arginine (from 0.1 to 100 microm) caused a concentration-dependent reduction of electromechanical response to EFS indicating a role for NO in this response. 4. Apamin (1 microm) reduced both IJP and r…

Fasting prior to transient cerebral ischemia reduces delayed neuronal necrosis.

1990

A transient brain ischemia of 30-min duration was induced by the four-vessel occlusion technique in normally fed and in 48-hr-fasted rats. Evaluation of brain damage 72 hr after ischemia showed that fasting reduced neuronal necrosis in the striatum, the neocortex, and the lateral part of the CA1 sector of hippocampus. Signs of status spongiosis in the pars reticulata of the substantia nigra were seen in 75% of fed rats and in only 19% of fasted rats. The protective effect was associated with reduction in mortality and in postischemic seizure incidence. The metabolic changes induced by fasting were evaluated before and during ischemia. After 30 min of four-vessel occlusion, fasted rats showe…

Cannabinoid receptor 1 modulates the autophagic flux independent of mTOR- and BECLIN1-complex

2013

Cannabinoid Receptor 1 (CB1) has been initially described as the receptor for Delta-9-Tetrahydrocannabinol in the central nervous system (CNS), mediating retrograde synaptic signaling of the endocannabinoid system. Beside its expression in various CNS regions, CB1 is ubiquituous in peripheral tissues, where it mediates, among other activities, the cell's energy homeostasis. We sought to examine the role of CB1 in the context of the evolutionarily conserved autophagic machinery, a main constituent of the regulation of the intracellular energy status. Manipulating CB1 by siRNA knockdown in mammalian cells caused an elevated autophagic flux, while the expression of autophagy-related genes rema…

2′,5′-oligoadenylate synthetase from a lower invertebrate, the marine sponge Geodia cydonium, does not need dsRNA for its enzymatic activity

2002

AbstractRecently, the presence of 2′,5′-linked oligoadenylates and a high 2′,5′-oligoadenylate synthetase activity were discovered in a lower invertebrate, the marine sponge Geodia cydonium. It has been demonstrated that mammalian 2–5A synthetase isozymes require a dsRNA cofactor for their enzymatic activity. Our results show that, unlike mammalian 2–5A synthetases, the 2–5A synthetase from the sponge acts in a dsRNA-independent manner in vitro. A prolonged incubation of the G. cydonium extract with a high concentration of a micrococcal nuclease had no effect on the activity of the 2–5A synthetase. At the same time, the micrococcal nuclease was effective within 30 min in degrading dsRNA nee…

The adenine nucleotide content of rat liver during infusions of carbohydrates and polyols

1972

Injection of large doses of fructose, sorbitol, or a mixture of glucose, fructose and xylitol in rats causes a drop of liver ATP, total adenine nucleotides and Pi and a rise of AMP, which is in agreement with data from the literature. These changes are considered as a transient disturbance of homeostasis by compounds which are rapidly phosporylated in the liver. This is confirmed by the fact that during continuous infusion of these and other compounds at doses of 1,5 g · kg−1 · h−1 there was no such change. It is concluded that infusions of fructose or of the other carbohydrates tested with rates not exceeding those recommended for parenteral nutrition (0,5 g · kg−1 · h−1) are not likely to…

Inhibition of gluconeogenesis by extracellular ATP in isolated rat hepatocytes.

1991

The aim of this study was to determine the effect of externally added ATP on gluconeogenesis by isolated hepatocytes from starved rats. High concentrations of extracellular ATP inhibited gluconeogenesis from lactate and pyruvate but not from glycerol or fructose. This inhibition was associated with an increase in intracellular adenosine contents. ADP, AMP, or adenosine but not guanosine 5'triphosphate, inosine 5' triphosphate, or adenine also inhibited gluconeogenesis. alpha, beta-Methylene-ATP, a nonmetabolizable structural analogue of ATP, did not affect the rate of gluconeogenesis. Intracellular ATP levels were increased by externally added ATP or adenosine, but ATP-to-ADP ratios in the…