RESUMEN
Frog skeletal muscle mainly utilizes the substrates glucose and lactate for energy metabolism. The goal of this study was to determine the effect of insulin on the uptake and metabolic fate of lactate and glucose at rest in skeletal muscle of the American bullfrog, Lithobates catesbeiana, under varying temperature regimens. We hypothesize that lactate and glucose metabolic pathways will respond differently to the presence of insulin in cold versus warm acclimated frog tissues, suggesting an interaction between temperature and metabolism under varying environmental conditions. We employed radiolabeled tracer techniques to measure in vitro uptake, oxidation, and incorporation of glucose and lactate into glycogen by isolated muscles from bullfrogs acclimated to 5 °C (cold) or 25 °C (warm). Isolated bundles from Sartorius muscles were incubated at 5 °C, 15 °C, or 25 °C, and in the presence and absence of 0.05 IU/mL bovine insulin. Insulin treatment in the warm acclimated and incubated frogs resulted in an increase in glucose incorporation into glycogen, and an increase in intracellular [glucose] of 0.5 µmol/g (P<0.05). Under the same conditions lactate incorporation into glycogen was reduced (P<0.05) in insulin-treated muscle. When compared to the warm treatment group, cold acclimation and incubation resulted in increased rates of glucose oxidation and glycogen synthesis, and a reduction in free intracellular glucose levels (P<0.05). When muscles from either acclimation group were incubated at an intermediate temperature of 15 °C, insulin's effect on substrate metabolism was attenuated or even reversed. Therefore, a significant interaction between insulin and acclimation condition in controlling skeletal muscle metabolism appears to exist. Our findings further suggest that one of insulin's actions in frog muscle is to increase glucose incorporation into glycogen, and to reduce reliance on lactate as the primary metabolic fuel.
Asunto(s)
Aclimatación , Insulina/farmacología , Músculo Esquelético/efectos de los fármacos , Rana catesbeiana/metabolismo , Temperatura , Animales , Dióxido de Carbono/metabolismo , Bovinos , Glucosa/metabolismo , Glucógeno/metabolismo , Técnicas In Vitro , Ácido Láctico/metabolismo , Masculino , Redes y Vías Metabólicas , Músculo Esquelético/metabolismo , Oxidación-ReducciónRESUMEN
Recent data suggest that opioids can activate immune-like cells of the central nervous system (glia). This opioid-induced glial activation is associated with decreased analgesia, owing to the release of proinflammatory mediators. Here, we examine in rats whether the putative microglial inhibitor, minocycline, may affect morphine-induced respiratory depression and/or morphine-induced reward (conditioned place preference). Systemic co-administration of minocycline significantly attenuated morphine-induced reductions in tidal volume, minute volume, inspiratory force, and expiratory force, but did not affect morphine-induced reductions in respiratory rate. Minocycline attenuation of respiratory depression was also paralleled with significant attenuation by minocycline of morphine-induced reductions in blood oxygen saturation. Minocycline also attenuated morphine conditioned place preference. Minocycline did not simply reduce all actions of morphine, as morphine analgesia was significantly potentiated by minocycline co-administration. Lastly, morphine dose-dependently increased cyclooxygenase-1 gene expression in a rat microglial cell line, an effect that was dose-dependently blocked by minocycline. Together, these data support that morphine can directly activate microglia in a minocycline-suppressible manner and suggest a pivotal role for minocycline-sensitive processes in the mechanisms of morphine-induced respiration depression, reward, and pain modulation.
Asunto(s)
Analgesia , Minociclina/farmacología , Morfina/farmacología , Insuficiencia Respiratoria/tratamiento farmacológico , Recompensa , Análisis de Varianza , Animales , Línea Celular , Células Cultivadas , Condicionamiento Operante/efectos de los fármacos , Ciclooxigenasa 1/metabolismo , Relación Dosis-Respuesta a Droga , Interacciones Farmacológicas , Masculino , Microglía/efectos de los fármacos , Microglía/metabolismo , Minociclina/uso terapéutico , Narcóticos/farmacología , Dolor/tratamiento farmacológico , Dimensión del Dolor , ARN Mensajero/metabolismo , Ratas , Ratas Sprague-Dawley , Insuficiencia Respiratoria/inducido químicamente , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Conducta Espacial/efectos de los fármacosRESUMEN
The excess postexercise oxygen consumption (EPOC), a measure of recovery costs, is known to be large in ectothermic vertebrates such as the desert iguana (Dipsosaurus dorsalis), especially after vigorous activity. To analyze the cause of these large recovery costs in a terrestrial ectotherm, Dipsosaurus were run for 15 s at maximal-intensity (distance 35.0+/-1.9 m; 2.33+/-0.13 m s(-1)) while O(2) uptake was monitored via open-flow respirometry. Muscle metabolites (adenylates, phosphocreatine, and lactate) were measured at rest and after 0, 3, 10, and 60 min of recovery. Cardiac and ventilatory activity during rest and recovery were measured, as were whole-body lactate and blood lactate, which were used to estimate total muscle activity. This vigorous activity was supported primarily by glycolysis (65%) and phosphocreatine hydrolysis (29%), with only a small contribution from aerobic metabolism (2.5%). Aerobic recovery lasted 43.8+/-4.6 min, and EPOC measured 0.166+/-0.025 mL O(2) g(-1). This was a large proportion (98%) of the total suprabasal metabolic cost of the activity to the animal. The various contributions to EPOC after this short but vigorous activity were quantified, and a majority of EPOC was accounted for. The two primary causes of EPOC were phosphocreatine repletion (32%-50%) and lactate glycogenesis (30%-47%). Four other components played smaller roles: ATP repletion (8%-13%), elevated ventilatory activity (2%), elevated cardiac activity (2%), and oxygen store resaturation (1%).
Asunto(s)
Metabolismo Energético/fisiología , Lagartos/fisiología , Consumo de Oxígeno/fisiología , Esfuerzo Físico/fisiología , Animales , Femenino , Masculino , Respiración , Carrera/fisiología , Factores de TiempoRESUMEN
This study examined glucose and lactate metabolism in an iguanid lizard, Dipsosaurus dorsalis, during rest and after activity patterned on field behavior (15 s of running at 1 m/s). Metabolite oxidation and incorporation into glycogen by the whole animal, the liver, and oxidative and glycolytic muscle fibers were measured using (14)C- and (13)C-labeled compounds. Results showed that lactate metabolism is more responsive to changes that occurred between rest and recovery, whereas glucose appears to play a more steady state role. After activity, lactate oxidation produced 57 times as much ATP during 1 h of recovery than did glucose oxidation. However, lactate oxidation rates were elevated for only 30 min after activity, while glucose oxidation remained elevated beyond 1 h. Lactate was the primary source for glycogen synthesis during recovery, and glucose was the main glycogenic substrate during rest. This study supports previous research showing that brief activity in D. dorsalis is primarily supported by glycolysis and phosphocreatine breakdown, but it also suggests that there may be less of a reliance on glycolysis and a greater reliance on phosphocreatine than previously shown. The findings presented here indicate that the metabolic consequences of the behaviorally relevant activity studied are less severe than has been suggested by studies using more extreme activity patterns.
Asunto(s)
Conducta Animal/fisiología , Clima Desértico , Iguanas/metabolismo , Adenosina Trifosfato/metabolismo , Animales , Femenino , Glucosa/metabolismo , Glucógeno/sangre , Glucógeno/metabolismo , Glucólisis/fisiología , Ácido Láctico/sangre , Ácido Láctico/metabolismo , Hígado/metabolismo , Masculino , Actividad Motora/fisiología , Músculo Esquelético/metabolismoRESUMEN
Previously, we found that phrynosomatid lizards, a diverse group common in the southwestern USA, vary markedly in fiber-type composition of the iliofibularis (a hindlimb muscle important in locomotion). Phrynosomatidae comprises three subclades: the closely related sand and horned lizards, and their relatives the Sceloporus group. The variation in muscle fiber-type composition for 11 phrynosomatid species is attributable mainly to differences between the sand- and horned-lizard subclades. Here, we expand the phrynosomatid database with three additional species and compare these results with data collected for 10 outgroup (distantly related) species. Our goal was to determine if the patterns found in Phrynosomatidae hold across a broader phylogenetic range of the extant lizards and to elucidate the evolution of muscle fiber-type composition and related traits. To allow for meaningful comparisons, data were collected from species that are primarily terrestrial and relatively small in size (3.5-65 g body mass). Results indicate that the fiber-type variation observed within the Phrynosomatidae almost spans the range of variation observed in our sample of 24 species from eight families. However, one species of Acanthodactylus (Lacertidae) had a consistent region of large tonic fibers (that did not stain darkly for either succinic dehydrogenase or myosin ATPase activity), a fiber-type only occasionally seen in the other 23 species examined. Many species have a large proportion of either fast-twitch glycolytic (FG; e.g. sand lizards and Aspidoscelis) or fast-twitch oxidative-glycolytic (FOG) fibers (e.g. horned lizards), with the slow-oxidative proportion occupying only 1-17% of the iliofibularis. Importantly, the negative relationship between FG and FOG composition observed in Phrynosomatidae appears to be a characteristic of lizards in general, and could lead to functional trade-offs in aspects of locomotor performance, as has previously been reported for Lacertidae. Reconstruction of ancestral trait values by use of phylogenetically based statistical methods indicates especially large changes in fiber-type composition during the evolution of horned lizards.
Asunto(s)
Lagartos/anatomía & histología , Fibras Musculares Esqueléticas/citología , Filogenia , Animales , Pesos y Medidas Corporales , Histocitoquímica , Lagartos/genética , Sudoeste de Estados Unidos , Especificidad de la EspecieRESUMEN
Intermittent activity, alternating bouts of activity and rest, can extend endurance relative to continuous locomotion. Utilizing a rapid fatiguing activity intensity (1.08 m s(-1)), Dipsosaurus dorsalis (n = 14) ran repeated bouts of varying durations (5, 15, or 30 s) interspersed with variable pause periods (100%, 200%, 400%, or 800% of the activity period) until exhausted. Total distance ran increased relative to continuous locomotion. The largest increases were seen when activity periods were limited to 5 s and pause periods were extended from 5 s to 20 s to 40 s (55, 118, and 193 m, respectively). To analyze these increases further, O(2) consumption was measured for six bouts of 5-s activity separated by either 5, 20, or 40 s (n = 8). The sum of elevated O(2) consumption during activity, pauses, and recovery increased significantly from 0.08 to 0.09 and 0.12 mL O(2) g(-1) as pause duration increased, primarily due to greater O(2) consumption during longer pause intervals. Postexercise recovery metabolism was a large cost (>57% of total) but did not differ among treatments. Overall, 40-s pauses were most expensive (absolutely and per unit distance) but provided the greatest endurance, likely due to further repletion of metabolites or removal of end products during the longer pause. In contrast, the shortest pause period was most economical but exhausted the animal most rapidly. Thus, a pattern of intermittent activity utilized by an animal may have energetic advantages that sometimes may be offset by behavioral costs associated with fatigue.
Asunto(s)
Metabolismo Energético/fisiología , Iguanas/fisiología , Locomoción/fisiología , Resistencia Física/fisiología , Análisis de Varianza , Animales , California , Clima Desértico , Consumo de Oxígeno/fisiología , Factores de TiempoRESUMEN
A regulated decrease in internal body temperature (Tb) appears to play a protective role against metabolic disruptions such as exposure to ambient hypoxia. This study examined the possibility that Tb depression is initiated when low internal oxygen levels trigger the release of adenosine, a neural modulator known to influence thermoregulation. We measured selected Tb of Anolis sagrei in a thermal gradient under varied ambient oxygen conditions and following the administration of the adenosine receptor antagonist 8-cyclopentyltheophylline (CPT). The average decrease in Tb observed following exposure to hypoxia (<10% O2) and following exhaustive exercise were 5 degrees and 3 degrees C, respectively, suggesting a role of oxygen availability on initiation of regulated hypothermia. When A. sagrei were run to exhaustion and recovered in hyperoxic (>95% O2) conditions, exercise-induced Tb depression was abolished. Administration of CPT similarly abolished decreased Tb due to both exercise and hypoxia. Trials using Dipsosaurus dorsalis indicate that elevated ambient oxygen during exercise does not influence blood pH or lactate accumulation, suggesting that these factors do not initiate changes in thermoregulatory setpoint following exhaustive exercise. We suggest that when oxygen is limiting, a decrease in arterial oxygen may trigger the release of adenosine, thereby altering the thermoregulatory setpoint.
Asunto(s)
Adenosina/metabolismo , Regulación de la Temperatura Corporal/efectos de los fármacos , Lagartos/fisiología , Oxígeno/farmacología , Teofilina/análogos & derivados , Análisis de Varianza , Animales , Regulación de la Temperatura Corporal/fisiología , Florida , Lagartos/metabolismo , Esfuerzo Físico/fisiología , Antagonistas de Receptores Purinérgicos P1 , Teofilina/farmacologíaRESUMEN
Lizards and many other animals often engage in locomotor behaviors that are of such short duration that physiological steady-state conditions are not attained. It is sometimes difficult to estimate the energetic costs of this type of locomotor activity. This difficulty is addressed by considering as reflective of the metabolic cost of activity (C(act)) not only the oxygen consumed during the activity itself, but also the excess post-exercise oxygen consumption (EPOC) and any excess metabolites persisting at the end of EPOC. Data from both lizards and mammals demonstrate that EPOC is the major energetic cost when activity is short and intense. This paper evaluates the major metabolic components of EPOC in lizards. We then examine how behavioral variables associated with locomotion (duration, intensity, frequency) can influence EPOC and C(act). Short and intense activity is much more expensive by this measure than is steady-state locomotion. Evidence is provided that intermittent activity of short duration can be more economical relative to single bouts of the same activity. Metabolic savings appear greatest when the pause period between behaviors is short. In contrast, endurance is enhanced by short activity periods and longer pause periods, suggesting a tradeoff between endurance and EPOC-related metabolic costs.