T Wang

..Such animals, however, must be able to restore digestive functions soon after feeding, and these transitions appear to occur at low metabolic costs...

..If we are to distinguish between the genetic, developmental and environmental influences underlying the various ventilatory responses to hypoxia, however, we must design future experiments with time domains in mind...

..To demonstrate the usefulness of this method, examples are provided from four different tissues and species: the human placenta, a rice field eel, a porcine heart and a turtle...

..We speculate that the ventricular separation has evolved in response to the need of maintaining high oxygen delivery while protecting the pulmonary circulation from oedema as result of high vascular pressures...

..The results are discussed within the context of recent studies on the cardiorespiratory physiology of frogs and turtles...

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..This verifies that the pressure differences originate within the ventricle, indicating that the large muscular ridge separates the ventricle during cardiac contraction...

..We conclude that increases in pulmonary blood flow associated with ventilation are not required to maintain resting rates of oxygen uptake and CO2 excretion in resting animals...

..In spite of the different oxygen availability of the two sides of the heart, the biochemical and functional properties are alike and the differences may instead be overcome by the coronary blood supply...

..Our results suggest adrenergic regulation of the systemic vasculature, rather than the pulmonary, may be an important factor in the development of intracardiac shunts...

..Stimulation of CO2 sensitive chemoreceptors and pulmonary stretch receptors appear to have interactive effects on the central generation of ventilatory output in toads...

..Cost of ventilation was estimated to be 17% during hypoxia but less than 1% during hypercapnia. Our data indicate that ventilation can be greatly elevated at a small energetic cost...

..We conclude from both our theoretical and experimental analyses that V. exanthematicus operates near the functional limits of its lung...

..This suggests that reductions in [O(2)] mediate cardiovascular adjustments, while ventilatory responses are caused by reduced Pa(O(2))...

..Thus, we predict that venous P(O(2)) (Pv(O(2))) is reduced from a fasting value of 5.2 kPa to 1.6 kPa during digestion...

..We propose that hyperkalemia may account for a large part of the depressed cardiac contractility during long-term anoxic submergence...

..It is concluded that the python ventricle is incapable of the pronounced and variable shunts of other snakes, because of its architecture and valvular mechanics...

..Nevertheless, heating rates were the same in untreated and atropinised animals, and cooling rates were significantly longer in atropinised animals, indicating that shunt patterns contribute little to heat exchange...

..Our results indicate that reptiles recruit Ca2+ from the SR for force development in a frequency and tissue dependent manner. This is discussed in the context of the development of high reptilian heart rates and blood pressures...

..However, increased levels of adrenaline and calcium may, at least partially, salvage cardiac function under prolonged periods of anoxia...

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..Thus, while the outer compact layer of the rattlesnake heart clearly has an extensive coronary supply, rattlesnakes sustain a high blood pressure and heart rate during activity without coronary artery blood supply...

..Instead, lipids are stored efficiently and help to prepare the spiders for the long periods of food deprivation that may occur as a consequence of their opportunistic feeding strategy...

..One explanation for the different ventilatory responses could be that digestion induces a more relaxed state with low responsiveness to ventilatory stimuli...

..There were no changes following anaesthesia in mean cellular haemoglobin concentration, [K+], [Cl-], [Na+], [lactate] or osmolarity. Toads fully recovered from anaesthesia after 24 h...

..These prolonged inspiratory times leads to less flow resistance and may explain that tidal volume could be increased substantially without a measurable energetic cost...

..The data provide evidence that NT is an important hormonal mediator of postprandial intestinal hyperemia in the python, but its involvement in mediating the cardiac responses to digestion may be relatively minor...

..It seems, therefore, that the elevated PCO2, occuring during the postprandial period, constitutes of a regulated response to maintain pH rather than a state-dependent change in ventilatory control...

..In conclusion, because precontraction with serotonin did not facilitate HPV, the required precontraction in alligators seems specific to ET-1, which implies that ET-1 plays an important permissive role for the HPV response in alligators...

..Hence, the extraordinarily large cost of digestion in P. molurus does not appear to correlate with increased function and growth of gastrointestinal organs but must be associated with other physiological processes...

..Our study strongly indicates that histamine regulates heart rate during the initial phase of digestion in pythons. This study describes a novel regulation of the vertebrate heart...

..3 versus 12.5 +/- 1.5 kPa in control versus atropinised eels, respectively. These results indicate, therefore, that reflex bradycardia does not contribute to maintenance of MO(2) and regulation of SMR by the European eel in hypoxia...

..This creates the situation whereby the same fH at the two temperatures can represent different values of sVO2...

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..We propose that alanine functions as a nitrogen depot during dehydration and is not an anaerobe product in this case...

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..Previous studies show high degrees of blood flow separation in the Crotalus heart, and this can only be explained by the coordinated actions of the septa and the prominent atrioventricular valves...

..The possibility of reducing air-breathing frequency may be energetically beneficial for the fish, leaving more of the aerobic scope for growth and other activities, due to the proposed energetic costs of surfacing behavior...

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..32 units). In conclusion, while recovery from the acidosis following exercise did not seem to be affected by digestion, the alkaline tide did slightly dampen the reduction in pH(a) during activity...

..Nonetheless, there was no indication of myocardial necrosis, as biochemical and energetic parameters were generally unaffected by anoxia...

..Thus, despite using strong and different preconditioning stimuli compared with earlier studies, the cardio-protective effect of preconditioning seems to be absent in rainbow trout hearts that are inherently more hypoxia-tolerant...

..Thus, although [K+]o significantly decreased twitch force, this detrimental effect was more than counteracted by the positive inotropic effect of lactic acid and adrenaline...

..Injection of the nitric oxide donor SNP caused a significant decrease in P(CV) and MCFP. Thus, nitric oxide seems to affect venous tone...

..This present study indicates, therefore, that ET(B)-receptors are responsible for the majority of the cardiovascular responses to ET-1 in Trachemys...

..Both species have a functionally separated heart, so it is possible that NO may exert a larger role in species with low pulmonary blood pressures, irrespective of lung complexity...

..8.2 and 13.9 kPa, respectively). Although these observations suggest that HPV is more pronounced in species with complex lungs and functionally divided hearts, it is also clear that other components are involved...

..Thus, nitric oxide is involved in regulation of basal vascular tone in the python, but neither nitric oxide nor prostaglandins mediate the vasodilatory action of NPgamma...

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..Thus, it is evident that stimulation of both alpha- and beta-adrenoreceptors affects venous tone in S. marmoratus...

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..To characterize physiologic responses of ball pythons (Python regius) following a minor surgical procedure and investigate the effects of 2 commonly used analgesics on this response...

..Therefore, it is likely that the increased blood flows during digestion are distributed exclusively to visceral organs and that the thermal conductance remains unaffected by the elevated metabolic rate during digestion...

..Possibly, nanosilver affects the gills externally, reducing the diffusion conductance which then leads to internal hypoxia during low water oxygen tensions (P(O2))...

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..The studies on cardiorespiratory responses to digestion may allow for a further understanding of the physiological and structural constraints that limits the ability of reptiles and amphibians to sustain high metabolic rates...

..An RVI response has then reappeared in birds, but based on activation of the NKCC. Alternatively, the absence of the RVI response may represent the most ancient condition, and could have evolved several times within vertebrates...

..Consistent with the small muscular ridge, systolic pressures were identical in the pulmonary and systemic arteries, but, the snakes, nevertheless, lived to reach body weights severalfold of their hatchling weight...

..In contrast, the pulmonary circulation was relatively unresponsive to BK...

..Furthermore, the constant arterial PCO2, in the absence of an alkaline tide, of omeprazole-treated snakes strongly suggests that pH rather than PCO2 normally affects chemoreceptor activity and ventilatory drive...

..In contrast, the pulmonary vasculature seems far less responsive to NO...

..This suggests that the temperature-independent reduction of metabolism was already in place by autumn before the tegus had entered winter dormancy...

..Below we review these two different strategies and discuss their possible mechanisms and physiological significance...

..In undisturbed toads, CAF increased with the same time course as BCF while heart rate remained relatively constant, suggesting redistribution of blood flow...

..We conclude that although there are considerable changes in gut thickness and absorptive properties after feeding, the smooth muscle and its control appear little affected...

..This breathing pattern was most pronounced during severe hypercapnia and particularly evident during the post-hypercapnic hyperpnea...

..Therefore, this study has demonstrated the presence of RSA in the HRV signal and a dual location for VPN in the rattlesnake. We suggest there to be a causal relationship between these two observations...