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Biomedical subjects

M L Glass

Publications and source records attributed to M L Glass.

At least 19 recordsLinked to original sources
PubMed1996

Characterization of the atrial natriuretic factor system in lungs of the toad Bufo paracnemis.

Blood pressure in the amphibian pulmonary circulation is relatively high because a single ventricle serves both the systemic and pulmonary circulation, creating a high degree of plasma filtration from pulmonary capillaries. Previous studies have shown that lung atrial natriuretic factor (ANF) may have an important physiological function in preventing edema in mammals. In this study, we report the presence of the complete ANF system in the lungs of the toad Bufo paracnemis. Radioimmunoassay of tissue homogenates revealed that toad lung ANF concentration was approximately twice as high (928.5 +/- 83.0 pg mg-1 protein) as that of lung tissue in mammals of a similar size. The amount of ANF was significantly higher in the left than in the right atrium (15.0 +/- 1.2 versus 1.9 +/- 0.8 ng mg-1 protein; N = 4, P < 0.001), while the ventricle contained 488.3 +/- 41.8 pg mg-1 protein. In extracts of both lungs and atria, high-performance liquid chromatography revealed two forms of the peptide; prohormone and a carboxy-terminal peptide of low molecular mass, which is the biologically active form of peptide. The presence of the prohormone suggests that ANF is synthesized in toad lungs and atria. Characterization of toad lung receptors by a competitive binding assay demonstrated three different subtypes of ANF receptors: the guanylyl cyclase (GC) receptors, GC-A and GC-B, as well as clearance (C) receptors. We conclude that the toad Bufo paracnemis has a well-developed complete ANF system in the lung, suggesting that it has a role in toad lung physiology.

Amino Acid Sequence↗
PubMed1995

Ventilatory responses to carboxyhaemoglobinaemia and hypoxic hypoxia in Bufo paracnemis.

The modality of the O2 drive to breathe was evaluated in unanaesthetized Bufo paracnemis. Carbon monoxide (CO) hypoxia was applied to reduce CaO2 (arterial O2 content). Arterial PO2 (PaO2) was reduced through inspiration of hypoxic gas mixtures (hypoxic hypoxia). Measurements included pulmonary ventilation, CaO2, PaO2, pHa, blood pressure and heart rate. Application of fractional concentrations of CO equivalent to 0.001 reduced CaO2 from 11.6 +/- 1.2 to 8.6 +/- 0.7 vol% (mean +/- S.E.M., N = 6) without any effect on heart rate, blood pressure or ventilation. Inspiration of fractional concentrations of CO equivalent to 0.01 reduced CaO2 to 5.1 +/- 0.7 vol%, which was accompanied by increased ventilation. This response, however, correlated with a decreased arterial pH. The effect of a fractional concentration of CO of 0.01 on ventilation was abolished by compensation of pH through bicarbonate infusion. Consequently, carboxyhaemoglobinaemia per se failed to increase ventilation. By contrast, reductions of PaO2 clearly stimulated ventilation, which indicates that O2 partial pressure provides the principal O2 stimulus to breathe in Bufo paracnemis.

Animals↗
PubMed1994

Ventilatory responses to hypoxia in the toad Bufo paracnemis before and after a decrease in haemoglobin oxygen-carrying capacity.

The ventilatory and cardiovascular effects of a decreased O2-carrying capacity of the blood were evaluated in the toad Bufo paracnemis. Pulmonary ventilation was monitored using a pneumotachographic technique. Chronic arterial catheters served to record both cardiac frequency and blood pressure and enabled the withdrawal of blood samples for analysis of pH and partial pressure of O2 (PO2). Haemoglobin concentrations were determined by the cyanmethaemoglobin method. The ventilatory response to hypoxia was not affected by the reduction in blood O2-carrying capacity, which suggests that PO2 rather than O2 content is the regulated variable. The reduction in capacity is accompanied by an increased normoxic heart rate and by a reversal of the hypoxic tachycardia normally observed.

Animals↗
PubMed1993

Temperature and central chemoreceptor drive to ventilation in toad (Bufo paracnemis).

The central chemoreceptor drive to ventilation was assessed in unanesthetized toads, Bufo paracnemis, exposed to three different temperatures: 15, 25 and 35 degrees C. The acid-base status of the fourth ventricle was manipulated by mock CSF perfusion. In additional experiments, arterial pH was varied by inspiration of hypercapnic gas mixtures. Ventilation was measured directly by pneumotachography and arterial blood samples were analyzed using electrodes for pH and PO2. Regardless of temperature, the ventilatory control of acid-base status was predominantly central. Moreover, an increase in temperature was accompanied by a proportional increase in the ventilatory response to chemoreceptor stimulation by either lowered mock CSF pH or hypercapnia. The alphastat hypothesis could not adequately account for the temperature effects on the ventilatory responses to hypercapnia or on air convection requirements in the toad.

Animals↗
PubMed1992

Central chemoreceptor drive to breathing in unanesthetized toads, Bufo paracnemis.

Central chemoreceptor drive to breathing was studied in unanesthetized toads, equipped with face masks to measure pulmonary ventilation and arterial catheters to analyze blood gases. Two series of experiments were performed. Expt. 1: The fourth cerebral ventricle was perfused with solutions of mock CSF, adjusted to stepwise decreasing pH values. Concomitant perfusion-induced increases of pulmonary ventilation, pHa and PaO2 were measured. Expt. 2: Inspiration of hypercapnic gas mixtures was applied to stimulate both central and peripheral chemoreceptors. Subsequently, only peripheral chemoreceptors were stimulated. This was accomplished by repeating the hypercapnic conditions while the fourth ventricle was perfused with mock CSF at pH 7.7. This procedure reduced the slope of the ventilatory response curve by about 80%. Taken together, the experiments suggest a highly dominant role of central chemoreceptors in the ventilatory acid-base regulation of the toad.

Animals↗
PubMed1992

Autonomic basis for hypoxia-induced hyperglycaemia in toads (Bufo paracnemis).

1. Toads were exposed to steady hypoxic conditions (inspired PO2 = 40 mmHg) for 60 min. 2. Within the exposure time, glucose concentrations rose from about 30 mg% to a steady level of 45 mg%. The development of hyperglycaemia reached a stable level within 40 min. 3. This effect was eliminated by treatment with either propranolol or atropine, suggesting combined cholinergic and adrenergic activation.

Animals↗
PubMed1992

Development of blood pressure and cardiac reflexes in the frog Pseudis paradoxsus.

Systemic arterial blood pressure and heart rate (fH) were measured in unanesthetized, unrestrained larvae and adults of the paradoxical frog, Pseudis paradoxus from São Paulo State in Brazil. Four developmental groups were used, representing the complete transition from aquatic larvae to primarily air-breathing adults. fH (49-66 beats/min) was not significantly affected by development, whereas mean arterial blood pressure was strongly affected, being lowest in the stage 37-39 larvae (10 mmHg), intermediate in the stage 44-45 larvae (18 mmHg), and highest in the juveniles and adults (31 and 30 mmHg, respectively). Blood pressure was not significantly correlated with body mass, which was greatest in the youngest larvae and smallest in the juveniles. In the youngest larvae studied (stages 37-39), lung ventilation was infrequent, causing a slight decrease in arterial blood pressure but no change in heart rate. Lung ventilation was more frequent in stages 44-45 larvae and nearly continuous in juveniles and adults floating at the surface. Bradycardia during both forced and voluntary diving was observed in almost every advanced larva, juvenile, and adult but in only one of four young larvae. Developmentally related changes in blood pressure were not complete until metamorphosis, whereas diving bradycardia was present at an earlier stage.

Aging↗
PubMed1992

Transient changes in blood pressure during spontaneous deep breaths in rats with sinoaortic deafferentation.

Sinoaortic deafferentation (SAD) in rats produces moderate increases in mean arterial pressure (MAP) along with a large augmentation of arterial pressure lability (APL). The mechanisms generating this APL are incompletely understood. To study the possible influence of breathing activity on APL in conscious SAD rats, we simultaneously recorded pulmonary ventilation and arterial blood pressure. The general pattern of pulmonary ventilation was the same in normal, sham-operated, and SAD rats. In all groups single large tidal volumes were regularly interposed in 1- to 2-min periods of shallower breathing. In SAD rats these single large inspirations were consistently accompanied by substantial and abrupt reductions of MAP, whereas this effect was markedly smaller or absent in normal and sham-operated rats. The data reflect the lack of fast moment-to-moment control of arterial pressure normally exerted by the aortic and carotid baroreceptors. In this context, effects of ventilatory changes must be considered along with humoral and neurogenic factors to explain APL after SAD.

Animals↗
PubMed1992

Effect of selective denervation of baroreceptors on pulmonary ventilation and arterial pressure lability in rat.

Earlier studies report that sinoaortic baroreceptor denervation (SAD) in rats causes moderate elevation of mean arterial pressure along with a marked increase of arterial pressure lability (APL). In this context, we studied the effects of selective aortic denervation (AD) or selective carotid denervation (CD) on the regulation of blood pressure. In addition, we evaluated the effects of selective or total baroreceptor denervation on pulmonary ventilation and ventilation-related changes of arterial pressure. Mean arterial pressure was evaluated by computer-assisted techniques, and ventilation was measured by whole body plethysmography on conscious freely moving rats. With this approach, equal increases of mean arterial pressure were obtained for rats that had undergone AD, CD, and SAD. The APL was higher in SAD rats than in selectively denervated rats. CD and AD rats had an elevated APL relative to sham-operated animals, and its increase was approximately equal for the two selectively denervated groups. Total as well as selective denervation had relatively small effects on ventilation and on the general pattern of breathing. In all groups, this pattern consisted of regular ventilation, periodically interrupted by single deeper breaths. In SAD, AD, and CD animals, these larger tidal volumes were associated with marked transient reductions of mean arterial pressure, whereas small decreases of pressure occurred in sham-operated rats. The results indicate that both groups of baroreceptors must be present to keep mean arterial pressure at its normal level. Moreover, both receptor groups are equally important in reducing APL. Ventilation contributes to generation of APL after total or selective baroreceptor removal. Such ventilation-induced pressure changes are kept at a minimum in baroreceptor-intact rats.

Animals↗
PubMed1989

Oxygen transfer kinetics of red blood cells of the turtle Pseudemys scripta elegans.

The kinetics of O2 uptake into, and release from, the red blood cells (RBC) of the turtle Pseudemys scripta elegans were determined with a stopped-flow technique at varied temperature (10-30 degrees C) and pH (7.5-7.9). The results were compared to those obtained for RBC of other vertebrates and related to morphometric and physiological data on gas/blood diffusion in turtle lungs. The O2 transfer conductance of RBC, G, for O2 release into high concentrations of dithionite, considered to represent the best estimate of true RBC transfer conductance for O2 uptake and release, averaged 0.17 +/- 0.01 at 30 degrees C, 0.13 +/- 0.01 at 20 degrees C, 0.09 +/- 0.01 at 10 degrees C (mean +/- SD, in mmol.min-1.Torr-1.(mlRBC)-1). These values are about one half the corresponding value for human RBC, and this difference may be due to the larger size of turtle RBC (volume, 327 microns 3) compared to human RBC (90 microns 3). The temperature dependence of G, Q10 = 1.3 indicates that, as in human RBC, diffusion through aqueous media is the main limiting factor for O2 exchange. Morphometric data on the lungs of Pseudemys scripta suggest that the resistance to O2 transfer by RBC is lower than that offered by the gas-blood barrier. The total apparent transfer resistance to CO, obtained from previous measurements of pulmonary diffusing capacity for CO in the same species, is much higher than that predicted from the combination of RBC O2 kinetics and morphometric data on gas-blood barrier.

Animals↗
PubMed1987

Control of breathing in an amphibian Bufo paracnemis: effects of temperature and hypoxia.

Lung ventilation was measured in the toad, Bufo paracnemis, weight 500-800 g, at 15, 25 and 32 degree C during normoxia and hypoxia (5, 10, and 15% inspired O2). Arterial blood gases were measured during normoxic breathing. Typically breath-holds alternated with ventilatory periods, which were initiated by a stepwise pulmonary deflation. Then a series of breaths consisting of both expiratory and inspiratory volumes followed. At the end of the period the lungs were inflated in several steps. Increased temperature markedly augmented ventilation mostly through a five-fold increase in the number of ventilatory periods per unit time. Ventilation was also enhanced by hypoxia and this response was greatest at the highest temperature. Arterial PO2 rose from 35 to 96 Torr when temperature increased from 15 to 32 degrees C. Bufo resembles reptiles regarding these responses.

Animals↗
PubMed1987

Pulmonary function of the green sea turtle, Chelonia mydas.

Lung volumes, oxygen uptake (VO2), end-tidal PO2, and PCO2, diffusing capacity of the lungs for CO (DLCO), pulmonary blood flow (QL) and respiratory frequency were measured in the green sea turtle (Chelonia mydas) (49-127 kg body wt). Mean lung volume (VL) determined from helium dilution was 57 ml/kg and physiological dead space volume (VD) was about 3.6 ml/kg. QL, determined from acetylene uptake during rebreathing, increased in proportion to VO2 with temperature. Therefore, constant O2 content difference was maintained between pulmonary arterial and venous blood. DLCO, measured using a rebreathing technique, was 0.04 ml X kg-1 X min-1 X Torr-1 at 25 degrees C. Several cardiopulmonary characteristics in C. mydas are advantageous to diving: large tidal volume relative to functional residual capacity promotes fast exchange of the alveolar gas when the turtle surfaces for breathing: and the concomitant rise of pulmonary blood flow and O2 uptake with temperature assures efficient O2 transport regardless of wide temperature variations encountered during migrations.

Animals↗
PubMed1987

Respiratory properties of blood and arterial blood gases in the tegu lizard: effects of temperature and hypercapnia.

The effects of body temperature and hypercapnia (7% inspired CO2) on arterial blood gases, plasma pH, and the characteristics of the blood oxygen dissociation curve were determined in Tegu lizards (Tupinambis nigropunctatus). Arterial pH fell from 7.59 to 7.50 when body temperature was increased from 25 to 35 degrees C. The pH/temperature coefficient (delta pH/delta t = -0.009 U/degrees C) was half of that predicted on the basis of 'constant relative alkalinity' and the alphastat hypothesis. The fall in plasma pH resulted from a decrease in plasma [HCO3-], and a rise in plasma Pco2. The O2 affinity of Tegu blood, expressed by the partial pressure at half saturation (P50), decreased with temperature in vitro from 42.3 to 49.6 torr at pH 7.4. The apparent enthalpy (delta H = -3.1 kcal/mol) is about 1/4 of that of human blood. In vivo, the arterial blood oxygen saturation decreased from 89% at 25 degrees to 82% at 35 degrees C. Arterial Po2 increased from 61 to 71 torr as expected from the right-shift of the oxygen dissociation curve. During environmental hypercapnia (7% CO2, 21% O2, 72% N2 inspired concentrations), arterial pH decreased to 7.28. Arterial O2 saturation remained constant and arterial Po2 increased from 61 to 85 torr due to the right-shift of the oxygen dissociation curve. The comparatively small effect of changes in temperature on the oxygen affinity of Tegu blood (directly according to the delta H value, and indirectly via changes in blood pH) results in a relatively small right shift of the oxygen dissociation curve, and accordingly in relatively high arterial and tissue Po2 values also at higher temperatures.

Animals↗
PubMed1986

The relative distribution of pulmocutaneous blood flow in Rana catesbeiana: effects of pulmonary or cutaneous hypoxia.

The distribution of pulmocutaneous heart output to lungs and skin was determined in non-anaesthetized, fully recovered bullfrogs (Rana catesbeiana) by application of the microsphere method in order to study the modulation of blood flow to different gas exchange sites in amphibians during environmental air and water hypoxia. The relative perfusion of various skin areas was found to be rather heterogeneously distributed with an over-proportionately high blood flow to the ventral body surface. This distribution of flow among different skin areas remained unaffected by any type of environmental hypoxia. The relative perfusion of lungs and skin, however, was significantly affected by the pattern of environmental oxygen partial pressure. The relative lung perfusion (approximately equal to 80% of pulmocutaneous flow in normoxic control conditions) was increased during water hypoxia, and reduced with lowered inspired PO2. This mechanism could be interpreted as a readjustment of blood flow towards the gas exchange site with higher oxygen partial pressure, but may also represent a mechanism to prevent oxygen loss from the body stores at gas exchange sites of low oxygen tension.

Animals↗
PubMed1981

Pulmonary diffusing capacity of the bullfrog (Rana catesbeiana).

Carbon monoxide diffusing capacity of the lungs (DLCO) was measured in bullfrogs, Rana catesbeiana (mean body weight 260 g) along with oxygen uptake, pulmonary perfusion and lung volume. The measurements were all performed by methods depending on mass-spectrometry. Pulmonary oxygen uptake, DLCO and perfusion all increased with body temperature. At 20 degrees C O2-uptake was 0.49 ml STPD . kg-1 . min-1 at rest and DLCO was 0.022 ml STPD . kg-1 . min-1 . Torr-1. At 30 degrees C the values for O2-uptake and DLCO approximately doubled. Lung volume was large (90 ml . kg-1) and independent of body temperature. Oxygen uptake and DLCO of the bullfrog were small compared to values for a similar-sized mammal but the ratios of DLCO to O2-uptake quite similar. Analysis of available data on DLCO and O2-uptake in ectotherms also suggests a close correlation between O2-uptake and DLCO.

Animals↗
PubMed1981

Acid-base regulation during heating and cooling in the lizard, Varanus exanthematicus.

Current concepts of acid-base balance in ectothermic animals require that arterial pH vary inversely with body temperature in order to maintain a constant OH-/H+ and constant net charge on proteins. The present study evaluates acid-base regulation in Varanus exanthematicus under various regimes of heating and cooling between 15 and 38 degrees C. Arterial blood was sampled during heating and cooling at various rates, using restrained and unrestrained animals with and without face masks. Arterial pH was found to have a small temperature dependence, i.e., pH = 7.66--0.005 (T). The slope (dpH/dT = -0.005), while significantly greater than zero (P less than 0.05), is much less than that required for a constant OH-/H+ or a constant imidazole alphastat (dpH/dT congruent to 0.018). The physiological mechanism that distinguishes this species from most other ectotherms is the presence of a ventilatory response to temperature-induced changes in CO2 production and O2 uptake, i.e., VE/VO2 is constant. This results in a constant O2 extraction and arterial saturation (approx. 90%), which is adaptive to the high aerobic requirements of this species.

Acid-Base Equilibrium↗
PubMed1979

Periodic breathing in the crocodile, Crocodylus niloticus: consequences for the gas exchange ratio and control of breathing.

The ventilatory pattern in the Nile crocodile consists of episodes of breathing, interrupted by periods of breath-holding, the latter occupying 80% of total time during normal breathing at 25 degrees C. End-tidal gas composition varied with the periodic breathing but PO2 was always high (PO2 less than 110 torr) and PCO2 low (PCO2 less than 25 torr). The alveolar gas exchange ratio, RE, was very low during the non-ventilatory periods (RE congruent to 0.5), but increased markedly during ventilation. Breathing of hypoxic and hpercapnic gases caused a pronounced decrease in the duration of breath-holds. Hypercapnia decreased breathing frequency during ventilatory periods, but increased tidal volume. The results are discussed in relation to the practice of prolonged breath-holding associated with diving in crocodiles.

Alligators and Crocodiles↗