Regulation of breathing and body temperature of a burrowing rodent during hypoxic-hypercapnia

Burrowing mammals usually have low respiratory sensitivity to hypoxia and hypercapnia. However, the interaction between ventilation (V), metabolism and body temperature (Tb) during hypoxic-hypercapnia has never been addressed. We tested the hypothesis that Clyomys bishopi, a burrowing rodent of the Brazilian cerrado, shows a small ventilatory response to hypoxic-hypercapnia, accompanied by a marked drop in Tb and metabolism. V, Tb and O-2 consumption (VO2) of C. bishopi were measured during exposure to air, hypoxia (10% and 7% O-2), hypercapnia (3% and 5% CO2) and hypoxic-hypercapnia (10% O-2 + 3% CO2). Hypoxia of 7% but not 10%, caused a significant increase in V, and a significant drop in Tb. Both hypoxic levels decreased VO2 and 7% O-2 significantly increased V/VO2. Hypercapnia of 5%, but not 3%, elicited a significant increase in V, although no significant change in Tb, VO2 or V/VO2 was detected. A combination of 10% O-2 and 3% CO2 had minor effects on V and Tb, while VO2 decreased and V/VO2 tended to increase. We conclude that C. bishopi has a low sensitivity not only to hypoxia and hypercapnia, but also to hypoxic-hypercapnia, manifested by a biphasic ventilatory response, a drop in metabolism and a tendency to increase V/VO2. The effect of hypoxic-hypercapnia was the summation of the hypoxia and hypercapnia effects, with respiratory responses tending to have hypercapnic patterns while metabolic responses, hypoxic patterns. (C) 2004 Elsevier B.V. All rights reserved.

Effects of temperature and hypercapnia on ventilation and breathing pattern in the lizard Uromastyx aegyptius microlepis

In most reptiles, the ventilatory response to hypercapnia consists of large increases in tidal volume (V-T), whereas the effects on breathing frequency (f(R)) are more variable. The increased V-T seems to arise from direct inhibition of pulmonary stretch receptors. Most reptiles also exhibit a transitory increase in ventilation upon removal of CO2 and this post-hypercapnic hyperpnea may consist of changes in both V-T and f(R). While it is well established that increased body temperature augments the ventilatory response to hypercapnia, the effects of temperature on the post-hypercapnic hyperpnea is less described. In the present study, we characterise the ventilatory response of the agamid lizard Uromastyx aegyptius to hypercapnia and upon the return to air at 25 and 35 degreesC. At both temperatures, hypercapnia caused large increases in V-T and small reductions in f(R), that were most pronounced at the higher temperature. The post-hypercapnic hyperpnea, which mainly consisted of increased fR, was numerically larger at 35 compared to 25 degreesC. However, when expressed as a proportion of the levels of ventilation reached during steady-state hypercapnia, the post-hypercapnic hyperpnea was largest at 25 degreesC. Some individuals exhibited buccal pumping where each expiratory thoracic breath was followed by numerous small forced inhalations caused by contractions of the buccal cavity. This breathing pattern was most pronounced during severe hypercapnia and particularly evident during the post-hypercapnic hyperpnea. (C) 2002 Published by Elsevier B.V.

Red blood cells from the South American rattlesnake (Crotalus durissus terrificus) regulate volume incompletely following osmotic shrinkage and swelling in vitro

The ability of rattlesnake (Crotalus durissus terrificus) red blood cells to volume regulate in vitro has been investigated. Blood was drawn through a catheter inserted in the dorsal aorta and equilibrated to gas mixtures of different composition. Cells shrunken osmotically by increasing the extracellular osmolarity from approximate to 291 mosm l(-1) (n = 3) to approximate to 632 mosm l(-1) (calculated) only partially regulated their volume back towards the original volume either at pH 7.51 +/- 0.05 (mean +/- S.D., n = 5) or pH 7.20 +/- 0.06 (mean +/- S.D., n = 3), There was no improvement of the regulatory volume increase at low haemoglobin oxygen saturation. The limited volume restoration was inhibited by separate additions of amiloride (10(-4) M) or DIDS (10(-4) M) suggesting involvement of the Na+/H+ and Cl-/HCO3- exchangers. Cells that were swollen osmotically by an approximate to 30% dilution of the extracellular medium also exhibited a limited ability to recover their volume. Therefore, these cells show little ability to volume regulate when exposed to in vitro conditions that shrink or swell the cell. (C) 2000 Elsevier B.V. All rights reserved.

Effects of temperature on lung and blood gases in the South American rattlesnake Crotalus durissus terrificus

The effects of temperature on lung and blood gases were measured in the South American rattlesnake (Crotalus durissus terrificus). Arterial blood and lung gas samples were obtained from chronically cannulated animals at 15, 25, and 35 degrees C. As expected for reptiles, arterial pH fell with increased temperature (0.018 U degrees C-1 between 15 and 25 degrees C and 0.011 U degrees C-1 between 25 and 35 degrees C) while lung gas PCO2 rose from 5.8 mmHg at 15 degrees C to 13.2 mmHg at 35 degrees C. Concurrently, lung gas PO2 declined from 132 mmHg at 15 degrees C to 120 mmHg at 35 degrees C, and arterial PO2 increased from 33 to 76 mmHg in that temperature range. Arterial haemoglobin O-2 saturation rose from 0.53 at 15 degrees C to 0.83 at 25 degrees C but became slightly reduced (0.77) with a further elevation of temperature to 35 degrees C. Arterial haemoglobin concentration increased from 1.96 to 2.53 mM between 15 and 35 degrees C, consistent with higher demands on oxygen delivery to tissues at elevated temperatures. Moreover, the substantial increase of haemoglobin O-2 saturation between 15 and 25 degrees C conforms to the idea that reduction of the central vascular right-to-left shunt (pulmonary bypass of systemic venous return) is associated with high metabolic demands. (C) 1998 Elsevier B.V. All rights reserved.

Arterial acid-base status during digestion and following vascular infusion of NaHCO3 and HCl in the South American rattlesnake, Crotalus durissus

Digestion is associated with gastric secretion that leads to an alkalinisation of the blood, termed the alkaline tide. Numerous studies on different reptiles and amphibians show that while plasma bicarbonate concentration ([HCO3-](pl)) increases substantially during digestion, arterial pH (pHa) remains virtually unchanged, due to a concurrent rise in arterial PCO2 (PaCO2) caused by a relative hypoventilation. This has led to the suggestion that postprandial amphibians and reptiles regulate pHa rather than PaCO2.Here we characterize blood gases in the South American rattlesnake (Crotalus durissus) during digestion and following systemic infusions of NaHCO3 and HCl in fasting animals to induce a metabolic alkalosis or acidosis in fasting animals. The magnitude of these acid-base disturbances were similar in magnitude to that mediated by digestion and exercise. Plasma [HCOT] increased from 18.4+/-1.5 to 23.7+/-1.0 mmol L-1 during digestion and was accompanied by a respiratory compensation where PaCO2 increased from 13.0+/-0.7 to 19.1+/-1.4 mm Hg at 24 h. As a result, pHa decreased slightly, but were significantly below fasting levels 36 h into digestion. Infusion of NaHCO3 (7 mmol kg(-1)) resulted in a 10 mmol L-1 increase in plasma [HCO3-] within 1 h and was accompanied by a rapid elevation of pHa (from 7.58+/-0.01 to 7.78+/-0.02). PaCO2, however, did not change following HCO3- infusion, which indicates a lack of respiratory compensation. Following infusion of HCl (4 mmol kg(-1)), plasma pHa decreased by 0.07 units and [HCO3-](pl) was reduced by 4.6 mmol L-1 within the first 3 h. PaCO2, however, was not affected and there was no evidence for respiratory compensation.Our data show that digesting rattlesnakes exhibit respiratory compensations to the alkaline tide, whereas artificially induced metabolic acid-base disturbances of same magnitude remain uncompensated. It seems difficult to envision that the central and peripheral chemoreceptors would experience different stimuli during these conditions. One explanation for the different ventilatory responses could be that digestion induces a more relaxed state with low responsiveness to ventilatory stimuli. (C) 2005 Elsevier B.V. All rights reserved.

Efficient robust optimization based on polynomial chaos and tabu search algorithm

The study of robust design methodologies and techniques has become a new topical area in design optimizations in nearly all engineering and applied science disciplines in the last 10 years due to inevitable and unavoidable imprecision or uncertainty which is existed in real word design problems. To develop a fast optimizer for robust designs, a methodology based on polynomial chaos and tabu search algorithm is proposed. In the methodology, the polynomial chaos is employed as a stochastic response surface model of the objective function to efficiently evaluate the robust performance parameter while a mechanism to assign expected fitness only to promising solutions is introduced in tabu search algorithm to minimize the requirement for determining robust metrics of intermediate solutions. The proposed methodology is applied to the robust design of a practical inverse problem with satisfactory results.

Locomotor and metabolic activities of Gymnostreptus olivaceus (Diplopoda, Spirostreptida) at different photoperiod conditions

In the present investigation the locomotor and the metabolic activity of Gymnostreptus olivaceus were studied, using 24-hr cycles at different photoperiods and constant temperature and RH. Locomotor activity was studied by the actography method and was reported as coefficients of nocturnalism [CN (N/N + D). 100]. The results showed a nocturnalism coefficient of 98,71% under normal photoperiod conditions and of 29,58% under inverted photoperiod conditions. In constant illumination, the CN of G. olivaceus was 88,22%, and in constant darkness, its rhythm was close to that of the normal photoperiod (CN = 94,92%). The metabolic activity was studied by manometric Warburg respirometry and lit was reported as mu l O-2 . g(-1). h(-1). The respiratory rate of G. olivaceus under normal photoperiod condition was higher at night than during the day (52,52 x 28,76), coinciding with the pattern of nocturnal locomotor activity of the animal. However, under conditions of inverted photoperiod, the millipede maintained its tendency toward a more intense nocturnal respiratory rate (50,35 x 39,14). Similar behaviours were observed under constant illumination and constant darkness, in which G. olivaceus again presented higher nocturnal respiratory rates than diurnal ones(85,84 x 53,48 and 73,18 x 57,0, respectively). The present experimental data suggests the persistence of an endogenous rhythm where the light may not be an important exogenous synchronizer of the activity of G. olivaceus, because it was insufficient to block the start of the biological clock and the natural tendency of higher nocturnal activities of millipedes, principally when the tests were performed in constant illumination or darkness (free-running tests).

Evaporative water loss and oxygen uptake in two casque-headed tree frogs, Aparasphenodon brunoi and Corythomantis greeningi (Anura, Hylidae)

Evaporative water loss (EWL) and oxygen uptake ((V) over dot o(2)) was measured in two species of tree frogs with cranial co-ossification, Aparasphenodon brunoi and Corythomantis greeningi. Both species use their head to seal the entrance of bromeliads, tree holes or rocky crevices used as shelters. EWL was significantly reduced in sheltered individuals of both species as compared with those exposed nude to desiccation. EWL per unit area through the head surface was significantly lower than the body skin for A. brunoi but not for C., greeningi. EWL per unit surface area through C. greeningi body skin was about 50% that of A. brunoi, indicating a less permeable skin in the former species. The relationship between cranial coossification and EWL is discussed. ((V) over dot o(2)) in A. brunoi was comparable with other anurans of similar size, whereas in C. greeningi, it was lower than predicted from body mass. Moreover, ((V) over dot o(2)), in C. greeningi showed less sensitivity to temperature increase than in A. brunoi. C. greeningi occurs in a drier environment than A. brunoi, and this appears to be reflected in their EWL and ((V) over dot o(2)) characteristics. (C) 1997 Elsevier B.V.

Molecular characterization of hemoglobin alpha-D chains from Geochelone carbonaria and Geochelone denticulata land turtles

In order to help elucidate the evolution of alpha-globins, the complete cDNA and amino acid sequences of Geochelone carbonaria and Geochelone denticulata land turtles alpha-D chains have been described. In G. carbonaria, the cDNA is 539 bp with ATG start codon located at position 46, TGA stop codon at position 469 and AATAAA polyadenylation signal at position 520. In G. denticulata, the cDNA is 536 bp with ATG start codon located at position 46, TGA stop codon at position 469 and AATAAA polyadenylation signal at position 517. Both cDNAs codify 141 amino acid residues, differing from each other in only four amino acid residues. When comparing with human Hb alpha-chain, alterations in important regions can be noted: alpha110 Ala-Gly, alpha114 Pro-Gly, alpha117 Phe-Tyr and alpha122 His-Gln. There is a high homology between the amino acids of these turtles when compared with chicken alpha-D chains, progressively decreasing when compared with human, crocodile, snake, frog and fish alpha-chains. Phylogenetic analysis of alpha-D chains shows that those of turtles are closer to those of birds than to snakes and lizards. (C) 2002 Elsevier B.V. All rights reserved.

Gluconeogenesis and glucose replacement rate during long-term fasting of Japanese quails

Gluconeogenic activity and kinetic parameters of glucose metabolism were estimated during the different phases of prolonged food deprivation in quails. Gluconeogenic activity, estimated from the rate of increase of incorporation of (HCO3-)-C-14 into circulating glucose, was significantly higher in fasted quails than in fed birds, whatever the period of food deprivation. However, gluconeogenic activity during phase II, although higher than in the fed state, was significantly lower than in quails fasted for 2 days (phase I) or in those on the final (phase III) period of starvation. Gluconeogenic activity did not differ significantly in birds from phases I and III. Rates of glucose replacement, estimated with [6-H-3]-glucose, were very high (20.5 mg . kg(-1). min(-1)) in fed quails and were markedly reduced (to about 42% of fed values) by fasting, no difference being observed between quails fasted for 2 and 5 days. Because of the poor condition of the birds, glucose replacement rates could not be measured during phase III. The present data are the first to provide direct evidence for the changes in gluconeogenesis which occur during prolonged food deprivation.

Chitinolytic activities in the gut of Aedes aegypti (Diptera : Culicidae) larvae and their role in digestion of chitin-rich structures

Mosquito larvae are believed to be capable of digesting chitin, an insoluble polysaccharide of N-acetylglucosamine, for their nutritional benefit. Studies based on physiological and biochemical assays were conducted in order to detect the presence of chitinase activities in the gut of the detritus-feeding Aedes aegypti larvae. Larvae placed for 24 h in suspensions of chitin azure were able to digest the ingested chitin. Semi-denaturing PAGE using glycol chitin and two fluorogenic substrate analogues showed the presence of two distinct chitinase activities: an endochitinase that catalyzed the hydrolysis of chitin and an endochitinase that cleaved the short substrates [4MU(GlcNAc)(3)] and [4MU(GlcNAc)(2)] that hydrolyzed the chitobioside [4MU(GlcNAc)(2)]. The endochitinase had an extremely broad pH-activity against glycol chitin and chitin azure, pH ranging from 4.0 to 10.0. When the substrate [4MU(GlcNAc)(3)] was used, two activities were observed at pH ranges 4.0-6.0 and 8.0-10.0. Chitinase activity against [4MU(GlcNAc)(3)] was detected throughout the gut with the highest specific activity in the hindgut. The pH of the gut contents was determined by observing color changes in gut after feeding the larvae with color indicator dyes. It was observed a correlation between the pH observed in the gut of feeding larvae (pH 10-6.0) and the optimum pH for gut chitinase activities. In this work, we report that gut chitinases may be involved in the digestion of chitin-containing structures and also in the partial degradation of the chitinous peritrophic matrix in the hindgut. (C) 2003 Elsevier B.V. All rights reserved.