Ventilation in two species of lizards during rest and activity

1. 1. Oxygen consumption, ventilation frequency and tidal volume were measured simultaneously in two lizards, Varanus gouldii and Sauromalus hispidus, during rest and maximal activity.2. 2. Ventilation frequency and tidal volume are almost identical in these species. The greater oxygen consumption during activity of Varanus results from a greater oxygen extraction from ventilated air.3. 3. Increased oxygen consumption during activity results from increments in tidal volume; ventilation frequency remains constant.4. 4. The thermal and weight dependence of ventilatory variables in reptiles is analyzed.5. 5. The capacity for oxygen extraction by saurian lungs is similar to that of mammals and birds, even at identical ventilation rates, in spite of their simple lung morphology.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33770/1/0000022.pd

A comparison of activities of metabolic enzymes in lizards and rats

1. 1. Protein-specific activities of metabolically important enzymes were measured in liver and skeletal muscle homogenates from three species of lizards, Sauromalus hispidus and Dipsosaurus dorsalis (Iguanidae) and Varanus gouldii (Varanidae), and laboratory rats.2. 2. Phosphofructokinase activity was relatively high in the muscle tissue of the iguanid lizards, which rely heavily on anaerobic metabolism during activity. Other enzymes had similar activities in all species of lizards.3. 3. The soluble (anaerobic) enzymes had equal activities in the lizards and the rat; however, the mitochondrial (aerobic) enzymes were approximately one-fifth as active in the reptiles.4. 4. This differential activity parallels differences in organismal oxygen consumption and is probably due to a lower number of mitochondria in the reptilian tissue. The implications of this differential activity for the evolution of homeothermy are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34051/1/0000328.pd

Blood physiology and oxygen transport during activity in two lizards, Varanus gouldii and Sauromalus hispidus

1. 1. Aspects of blood physiology--hematocrit, oxygen capacity and affinity, lactate content, pH and composition of blood buffers--were investigated in the lizards Varanus gouldii and Sauromalus hispidus during activity at different temperatures.2. 2. Although oxygen capacity and affinity, resting pH and lactate levels, bicarbonate and phosphate concentrations are nearly identical in both species, only Sauromalus sustains a decrease in blood pH during activity, accompanied by a decrease in oxygen capacity and affinity, high levels of lactate production and exhaustion.3. 3. Non-carbonic blood buffers prevent a change in blood pH in Varanus. Lungs of great surface area facilitate exchange of oxygen and carbon dioxide, and Varanus undergoes only moderate lactate generation and remains aerobic during activity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33772/1/0000024.pd

The effect of activity on oxygen consumption, oxygen debt, and heart rate in the lizards Varanus gouldii and sauromalus hispidus

Oxygen consumption and heart rate were measured during rest and activity in the lizards Varanus gouldii and Sauromalus hispidus . Oxygen debt was calculated from postactive oxygen consumption. Standard metabolic rates of the two animals are similar but Varanus consumes much more oxygen during activity than does Sauromalus (Fig. 1–3). The latter has a constant active metabolic rate above 30 ° C and accumulates a large oxygen debt, which is repayed slowly (Fig. 4). Varanus recovers rapidly from activity (Fig. 5), presumably because of the smaller lactacid debt incurred. Heart rate increment in Sauromalus is high (Fig. 8). This variable cannot be responsible for the limitation of active oxygen consumption; calculations of oxygen pulse suggest that an inability to increase A-V difference and/or stroke volume are implicated (Fig. 9). Varanus have evolved mechanisms to sustain high levels of oxygen consumption superior to those of other reptiles investigated. The role of anaerobiosis in the biology of both animals is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47108/1/359_2004_Article_BF00694220.pd

Thermal Sensitivity of Swimming Performance and Muscle Contraction in Northern and Southern Populations of Tree Frogs (Hyla Crucifer)

The effects of temperature on sprint swimming ability and muscle contractile properties were examined in northern and southern populations of the holarctic tree frog, Hyla crucifer Wied-Neuwied, acclimated to 20–23°C. Maximal swimming velocities of 29 (southern) and 32 (northern) cms−1 and stroke frequencies of 4.1 (southern) and 5.5 (northern) strokes s-1 were attained at 30°C, and maximal stroke lengths (i.e. distance moved per stroke) of 8.0 (southern) and 7.4 (northern) cm at 20°C. The thermal dependence of swimming velocity decreases with increasing temperature (e.g. Q10 = 4.0 from 6 to 10°C, 1.2 from 20 to 30°C), as reported for locomotion in other ectothermic vertebrates. Over a temperature range of l.5-30°C, velocity increases by a factor of 5.5, frequency by a factor of 4, and length by a factor of 1.7. Thus, increased velocity at higher temperatures can be attributed mostly to increased stroke frequency; increments in stroke length contribute less. Muscle contractile properties have similar thermal dependencies to those of other vertebrates: rate processes [including twitch time-to-peak tension (TPT), twitch half-relaxation time (RT½), maximal rate of tetanic tension development and isotonic shortening velocity] are much more sensitive to temperature than is force generation (twitch and tetanic tension). Below 8°C, stroke frequency is limited by twitch contraction time (TPT + RT½), and leg extension in a swimming stroke by TPT. At higher temperatures, the thermal dependence of stroke time is lower than that of contraction time. Neither locomotor nor muscle contractile properties are different between the two populations (except for twitch tension at low temperatures). Inflexibility in the thermal dependence of muscle contraction and locomotion in this species may help to explain differences in breeding phenologies between northern and southern populations

Evolutionary response of Escherichia coli to thermal stress

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected].

Effects of activity and temperature on aerobic and anaerobic metabolism in the Galapagos marine iguana

1 Standard and maximal levels of oxygen consumption, and lactate production during burst activity were determined in the Galapagos marine iguana, Amblyrhynchus cristatus . This semiaquatic lizard sustains vigorous activity at relatively low body temperatures during underwater feeding (<25°C).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47117/1/360_2004_Article_BF00691052.pd

Growth hormone as concomitant treatment in severe fibromyalgia associated with low IGF-1 serum levels. A pilot study

<p>Abstract</p> <p>Background</p> <p>There is evidence of functional growth hormone (GH) deficiency, expressed by means of low insulin-like growth factor 1 (IGF-1) serum levels, in a subset of fibromyalgia patients. The efficacy of GH versus placebo has been previously suggested in this population. We investigated the efficacy and safety of low dose GH as an adjunct to standard therapy in the treatment of severe, prolonged and well-treated fibromyalgia patients with low IGF-1 levels.</p> <p>Methods</p> <p>Twenty-four patients were enrolled in a randomized, open-label, best available care-controlled study. Patients were randomly assigned to receive either 0.0125 mg/kg/d of GH subcutaneously (titrated depending on IGF-1) added to standard therapy or standard therapy alone during one year. The number of tender points, the Fibromyalgia Impact Questionnaire (FIQ) and the EuroQol 5D (EQ-5D), including a Quality of Life visual analogic scale (EQ-VAS) were assessed at different time-points.</p> <p>Results</p> <p>At the end of the study, the GH group showed a 60% reduction in the mean number of tender points (pairs) compared to the control group (p < 0.05; 3.25 ± 0.8 <it>vs</it>. 8.25 ± 0.9). Similar improvements were observed in FIQ score (p < 0.05) and EQ-VAS scale (p < 0.001). There was a prompt response to GH administration, with most patients showing improvement within the first months in most of the outcomes. The concomitant administration of GH and standard therapy was well tolerated, and no patients discontinued the study due to adverse events.</p> <p>Conclusion</p> <p>The present findings indicate the advantage of adding a daily GH dose to the standard therapy in a subset of severe fibromyalgia patients with low IGF-1 serum levels.</p> <p>Trial Registration</p> <p>NCT00497562 (ClinicalTrials.gov).</p