Metabolic and ventilatory responses to hypoxia in two altitudinal populations of the toad, Bufo bankorensis

Effects of hypoxia on resting oxygen consumption ( ), lung ventilation, and heart rate at different ambient P_O2 were compared between lowland and high altitude populations of the toad, Bufo bankorensis. Resting decreased significantly in mild hypoxia (P_O2=120 mm Hg) at 10°C and in moderate hypoxia (P_O2=80 mm Hg) at 25°C in both altitudinal populations; however, resting did not differ significantly between the two populations. Numbers of lung ventilation periods (VP) and total inspired volume (V_L) did not change with P_O2 at 10°C, but did increase at moderate and severe hypoxia (40 mm Hg), respectively, at 25°C. Resting heart rates did not change during hypoxia and did not differ between altitude populations. The results suggest (1) the effect of P_O2 change on should be considered in future studies involving transfer of anurans to a different altitude; and (2) the metabolic and ventilatory physiology in B. bankorensis does not compensate for the low temperature and P_O2 at high altitude.     

Ingested energy differs between populations of the toad Bufo bankorensis from different altitudes

We measured ingested energy (E(i)) and apparent digestibility efficiency (ADE) in two populations of Bufo bankorensis from different altitudes at three temperatures and during two seasons to test the hypothesis that the optimal temperature range (T(opt)) for E(i) and ADE has shifted to the lower range in highland toads and winter toads. The T(opt) for E(i) was 22 degrees C for the lowland and highland toads and did not vary between seasons, thus falsifying the hypothesis. ADE of the toads was 96%-99% at 15 degrees -30 degrees C, and there was no difference between populations or seasons. Furthermore, when fed with fast-moving prey, the toads from both altitudes had similarly low E(i) at 15 degrees C; when fed with slow-moving prey, the highland toads increased E(i) at 15 degrees C, but the lowland toads did not. These results suggest that the toads from different altitudes had different appetites, even though their feeding locomotion was hampered in both populations at low temperatures.     

Temperature and humidity alter prolactin receptor expression in the skin of toad (Bufo bankorensis and Bufo melanostictus)

Bufo bankorensis and Bufo melanostictus, the only two species of Bufonidae genus in Taiwan, live in habitats that differ in altitude and humidity. This study tested the hypothesis that prolactin receptor (PRLR) expression responds to environmental change. Western blot analysis showed that the PRLR protein was widely distributed in brain, lung, liver, kidney, dorsal skin and ventral skin of toads. The level PRLR protein was elevated in the dorsal skin of the two toad species treated with dry or wet conditions for 14 days. The increase in PRLR of dorsal skin in B. bankorensis was higher than that in B. melanostictus. This experimental result suggests that B. bankorensis secretes more mucus to reduce water evaporation from its thinner cuticle than B. melanostictus. The expression of PRLR protein was increased in the lung of B. bankorensis and decreased in the lung of B. melanostictus. Moreover, PRLR protein levels were increased in the kidneys in the two species toad, likely due to reduction in water lost through lung and urine. The two toad species were subjected to varying temperatures (25 degrees C, 15 degrees C and 10 degrees C) for 14 days. The lowest PRLR protein expression was observed at 10 degrees C. Comparison of the decreasing trend in PRLR protein levels demonstrated that the variation in B. bankorensis was significantly higher than that in B. melanostictus. Comparisons of variation in PRLR protein expression in the two species under different environments suggest that B. bankorensis is more adaptable to different environments than B. melanostictus.     

Reproductive characteristics of Bufo bankorensis at two elevations in Taiwan

We compared the reproductive characteristics of two populations of Bufo bankorensis in central Taiwan, one inhabiting a temperate climate (Meifong, 2100 m), the other inhabiting a subtropical climate (Wushe, 1100 m). We determined ovary status, spermatogenetic activity, fat body and liver mass cycles, and plasma 17-betaestradiol and androgen levels over a 14 month period. B. bankorensis from both populations are prolonged breeders but the temperate population exhibits breeding activity throughout the year, while the subtropical population only breeds from September to March. Their spermatogenic cycles are continuous, and their spermatogenetic activities are invariably at stage 6, in which spermatozoa are predominant in the seminiferous tubule. Both populations show monthly variations in plasma androgen and 17-betaestradiol levels, but follow different patterns. Ovary mass is larger in the temperate than in the subtropical population. The reproduction differences of two elevation toads could be reflected by adaptations to the local environmental regimes of its habitat. The reproductive patterns of these populations of Bufo bankorensis are also compared to those of sympatric and allopatric populations of five anurans studied from sites throughout Taiwan.     

Seasonal changes in the preferred body temperature, cardiovascular, and respiratory responses to hypoxia in the toad, Bufo paracnemis

Estivation is accompanied by a reduction of oxygen consumption in amphibians during drought. We tested the hypothesis that, during the dry season, the toad Bufo paracnemis selects a lower preferred body temperature (T(b)), and would be less sensitive to hypoxia, than during its active period. Therefore, during winter (dry season in S?o Paulo state, Brazil) and summer, we measured the effects of hypoxia (7% inspired O(2)) on preferred T(b). Additionally, pulmonary ventilation, heart rate, blood pressure, and oxygen consumption were also measured in toads at 15 and 25 degrees C. Blood gases were measured at 25 degrees C. Oxygen consumption was significantly higher during summer in toads at 25 degrees C. Under normoxia, preferred T(b) was higher during summer than during winter, and hypoxia caused a drop in preferred T(b) during both seasons. In both seasons, toads at 15 degrees C showed reduced pulmonary ventilation, heart rate, and blood pressure, and hypoxia had no effect. At 25 degrees C during summer only, hypoxia caused an increase in ventilation. Season had no effect on blood gases. We conclude that B. paracnemis displays an endogenous seasonal pattern of thermoregulation and control of ventilation. The decreased preferred T(b) and the physiological responses to hypoxia may be beneficial to toads encountering drought and when food is not available.     

Mating patterns of Minshan's toad (Bufo minshanicus) from three populations along an altitudinal gradient

The large-male mating advantage and size-assortative mating are two different size-based patterns, which deviate from random mating in toads. These two pairing patterns may arise due to female choice, male-male competition, male choice, or a combination of these. This study investigated the mating system of Minshan's toad (Bufo minshanicus) from three populations along an altitudinal gradient during two breeding reasons in the northeastern Tibetan plateau. Our study shows that males found in amplexus with females were larger on average than non-amplectant males in two sites with higher operational sex ratios. Similarly, in those sites, males and females found in amplexus maintained an optimal size ratio. These data suggest that male-male competition leads to size-assortative mating in the lack of mate choice (female and male mate choice) by Minshan's toad, as larger males performed higher frequencies for taking-over other low quality ones with amplectant females.     

Antidiuretic responses to osmotic cutaneous stimulation in the toad,Bufo arenarum

Summary Osmotic stimulation of the skin of the toadBufo arenarum with isotonic (115 mM) or hypertonic (400 mM) NaCl solutions produced a marked and reversible antidiuresis within 5 min. No changes in plasma osmolarity were detected in the course of this response.Hypophysectomized animals exhibited a lower and delayed antidiuresis when exposed to a hypertonic environment (400 mM NaCl). This antidiuretic response was drastically reduced in normal toads after ten consecutive days of administration of the sympatoplexic guanethidine.The existence of a feed-forward control of urine production initiated by cutaneous osmotic sensors and involving an adrenergic component is proposed.     

Tectal responses to potassium loads and subsequent visual stimuli in the toad, Bufo bufo

Calling male toads were tested behaviourally for their prey catching responses to wormlike stimuli and assigned to groups of non-hungry and hungry depending on their prey catching motivation before being prepared for visual unit, massed unit and slow potential shift (SPS) recording from the optic tectum. Control recordings to visual stimuli were made before recording the effects of application of isotonic solutions containing concentrations of 0-41 mM K(+). Application of solution was followed by presentation of the visual stimulus while the solution still bathed the tectum. The best tectal responses were made to large square visual stimuli in the non-hungry toads, perhaps because recordings were made in the breeding season. Responses of the tectum to solution addition were significant in the concentration range of 7-17 mM K(+). Hungry toads showed an earlier, smaller response than non-hungry (sexually motivated) animals. When the visual stimulus was presented, there were unit and massed unit responses at all bathing solution concentrations, which were larger in non-hungry animals. These experiments revealed that toads motivated to feed respond earlier than non-hungry toads to application of artificial CSF to the tectum, though non-hungry toads responded best to the subsequent visual stimulus.     

The ventilatory responses of the caecilian Typhlonectes natans to hypoxia and hypercapnia

Typhlonectes natans empty their lungs in a single extended exhalation and subsequently fill their lungs by using a series of 10-20 inspiratory buccal oscillations. These animals always use this breathing pattern, which effectively separates inspiratory and expiratory airflows, unlike most urodele and anuran amphibians that may use one to many buccal oscillations for lung inflation and typically mix expired and inspired gases. Aquatic hypoxia had no significant effect on the breathing pattern or mechanics in these animals. Aerial hypoxia stimulated ventilatory frequency and increased the number of inspiratory oscillations but had little effect on inspiratory and expiratory tidal volume. Aquatic hypercapnia elicited a large significant increase in air-breathing frequency and minute ventilation compared to the small stimulation of minute ventilation seen during aerial hypercapnia. Some animals responded to aquatic hypercapnia with a series of three or four closely spaced breaths separated by long nonventilatory periods. Overall, T. natans showed little capacity to modulate expiratory or inspiratory tidal volumes and depended heavily on changing air-breathing frequency to meet hypoxic and hypercapnic challenges. These responses are different from those of anurans or urodeles studied to date, which modulate both the number of ventilatory oscillations in lung-inflation cycles and the degree of lung inflation when challenged with peripheral or central chemoreceptor stimulation.     

Antidiuretic responses to osmotic, ionic or volume stimulation of the brain in the unanesthetized toad, Bufo arenarum Hensel

Single injections of 15 microliter of 1 M NaCl or 2M sucrose into the carotid system of normal unanesthetized toads induced a rapid and significant decrease of urine production. This appears to be the first report on the existence of a Verney-like phenomena in a non-mammalian vertebrate. This antidiuresis was blocked out in the hypophysectomized diencephalic lesioned animal. Concurrently, small volumes (4 microliters) of 1 M NaCl but not 2 M sucrose also induced antidiuresis when injected into the midbrain tegmentum of normal but not of hypophysectomized diencephalic lesioned toads. Larger volumes (6 microliters) of 2 M sucrose were needed to induce a similar antidiuresis in normals. Furthermore, even larger volumes (more than 8 microliters) of any of both solutions were able to induce oliguria in normal as well as in hypophysectomized toads. On the basis of these results, the following conclusion would be drawn: the brain of the toad is able to detect ionic and osmotic stimuli, these stimuli apparently affect different receptors in the brain, the antidiuresis initiated by these mechanisms is dependent on diencephalic integrity.     

Metabolic and ventilatory responses to steady state exercise relative to lactate thresholds

The metabolic and ventilatory responses to steady state submaximal exercise on the cycle ergometer were compared at four intensities in 8 healthy subjects. The trials were performed so that, after a 10 min adaptation period, power output was adjusted to maintain steady state VO2 for 30 min at values equivalent to: (1) the aerobic threshold (AeT); (2) between the aerobic and the anaerobic threshold (AeTAnT); (3) the anaerobic threshold (AnT); and (4) between the anaerobic threshold and VO2max (AnTmax). Blood lactate concentration and ventilatory equivalents for O2 and CO2 demonstrated steady state values during the last 20 min of exercise at the AeT, AeAnT and AnT intensities, but increased progressively until fatigue in the AnTmax trial (mean time = 16 min). Serum glycerol levels were significantly higher at 40 min of exercise on the AeAnT and the AnT when compared to AeT, while the respiratory exchange ratios were not significantly different from each other. Thus, metabolic and ventilatory steady state can be maintained during prolonged exercise at intensities up to and including the AnT, and fat continues to be a major fuel source when exercise intensities are increased from the AeT to the AnT in steady state conditions. The blood lactate response to exercise suggests that, for the organism as a whole, anaerobic glycolysis plays a minor role in the energy release system at exercise intensities upt to and including the AnT during steady state conditions.     

Egg production in the Common toad, Bufo bufo

The number and size of eggs produced by the Common toad (Bufo bufo) was investigated at a site in southern England. There was a trend within the population as a whole for egg weight, egg number and ovary weight to increase with female size, as defined by body length and body weight. However, with use of partial correlation analysis to remove the effects of female size from the data, some of these trends changed. Thus, for females of the same size, although egg number increased with ovary weight, no significant correlation was found between egg weight and ovary weight whilst egg weight became negatively correlated with egg number. The possible significance of variation in egg weight on tadpole survival and female reproductive success is discussed.     

Metabolic and endocrine responses to graded exercise under acute hypoxia

Eight male subjects (24 +/- 1 years old) performed graded ergocycle exercises in normoxic (N) and acute hypoxic (H) conditions (14.5% O2). VO2max decreased from 55.5 +/- 1.3 to 45.8 +/- 1.4 ml . kg-1 . min-1 in H condition. Plasma glucose and free fatty acid concentrations remained unchanged throughout exercise in both conditions. Increase in blood lactate concentration was associated with relative workload in both conditions. At VO2max lactate concentrations were similar in the two conditions, plasma insulin, glucagon, and LH concentrations did not significantly change in either. Plasma delta 4-androstenedione and testosterone increased in a similar manner in both conditions. Finally plasma norepinephrine concentration reached at VO2max was significantly lower in hypoxia. These results suggest that acute moderate hypoxia does not affect metabolic and hormonal responses to short exercise performed at similar relative workloads, i.e. when the reduction of VO2max due to hypoxia is taken into consideration. The lower catecholamine response to maximal exercise under acute hypoxia might suggest that the sympathetic response could be related to relative as well as absolute workloads.     

The effects of intermittent exposure to hypoxia during endurance exercise training on the ventilatory responses to hypoxia and hypercapnia in humans

The present study was performed to investigate the effects of a combination of intermittent exposure to hypoxia during exercise training for short periods on ventilatory responses to hypoxia and hypercapnia (HVR and HCVR respectively) in humans. In a hypobaric chamber at a simulated altitude of 4,500 m (barometric pressure 432 mmHg), seven subjects (training group) performed exercise training for 6 consecutive days (30 min · day⁻¹), while six subjects (control group) were inactive during the same period. The HVR, HCVR and maximal oxygen uptake (V˙O_{2 max}) for each subject were measured at sea level before (pre) and after exposure to intermittent hypoxia. The post exposure test was carried out twice, i.e. on the 1st day and 1 week post exposure. It was found that HVR, as an index of peripheral chemosensitivity to hypoxia, was increased significantly (P < 0.05) in the control group after intermittent exposure to hypoxia. In contrast, there was no significant increase in HVR in the training group after exposure. The HCVR in both groups was not changed by intermittent exposure to hypoxia, while V˙O_{2 max} increased significantly in the training group. These results would suggest that endurance training during intermittent exposure to hypoxia depresses the increment of chemosensitivity to hypoxia, and that intermittent exposure to hypoxia in the presence or absence of exercise training does not induce an increase in the chemosensitivity to hypercapnia in humans. Accepted: 18 March 1998     

Metabolic adjustments in two Amazonian cichlids exposed to hypoxia and anoxia

The effects of graded hypoxia on the physiological and biochemical responses were examined in two closely related species of cichlids of the Amazon: Astronotus crassipinnis and Symphysodon aequifasciatus. Ten fish of each species were exposed to graded hypoxia for 8 h in seven oxygen concentrations (5.92, 3.15, 1.54, 0.79, 0.60, 0.34, and 0.06 mg O(2) L(-)(1)), with the aim to evaluate hypoxia tolerance and metabolic adjustments, where plasma glucose and lactate levels, hepatic and muscle glycogen contents, and maximum enzyme activities (PK, LDH, MDH and CS) in skeletal and cardiac muscles were measured. Another experimental set was done to quantify oxygen consumption (MO(2)) and opercular movements in two oxygen concentrations. Hypoxia tolerance differed between the two species. Astronotus crassipinnis was able to tolerate anoxia for 178 min while S. aequifasciatus was able to withstand 222 min exposure in deep hypoxia (0.75 mg O(2) L(-)(1)). Suppressed MO(2) was observed during exposure to 0.34 (A. crassipinnis) and 0.79 mg O(2) L(-)(1) (S. aequifasciatus), while opercular movements increased in both species exposed to hypoxia. Higher levels of muscle and liver glycogen and larger hypoxia-induced increases in plasma glucose and lactate were observed in A. crassipinnis, which showed a higher degree of hypoxia tolerance. Changes in enzyme levels were tissue-specific and differed between species suggesting differential abilities in down-regulating oxidative pathways and increasing anaerobic metabolism. Based on the present data, we conclude that these animals are good anaerobes and highly adapted to their environment, which is allowed by their abilities to regulate metabolic pathways and adjust their enzyme levels.