Pulmonary gas exchange in panting dogs

Pulmonary gas exchange during panting was studied in seven conscious dogs (32 kg mean body wt) provided with a chronic tracheostomy and an exteriorized carotid artery loop. The animals were acutely exposed to moderately elevated ambient temperature (27.5 degrees C, 65% relative humidity) for 2 h. O2 and CO2 in the tracheostomy tube were continuously monitored by mass spectrometry using a special sample-hold phase-locked sampling technique. PO2 and PCO2 were determined in blood samples obtained from the carotid artery. During the exposure to heat, central body temperature remained unchanged (38.6 +/- 0.6 degrees C) while all animals rapidly switched to steady shallow panting at frequencies close to the resonant frequency of the respiratory system. During panting, the following values were measured (means +/- SD): breathing frequency, 313 +/- 19 breaths/min; tidal volume, 167 +/- 21 ml; total ventilation, 52 +/- 9 l/min; effective alveolar ventilation, 5.5 +/- 1.3 l/min; PaO2, 106.2 +/- 5.9 Torr; PaCO2, 27.2 +/- 3.9 Torr; end-tidal-arterial PO2 difference [(PE' - Pa)O2], 26.0 +/- 5.3 Torr; and arterial-end-tidal PCO2 difference, [(Pa - PE')CO2], 14.9 +/- 2.5 Torr. On the basis of the classical ideal alveolar air approach, parallel dead-space ventilation accounted for 54% of alveolar ventilation and 66% of the (PE' - Pa)O2 difference. But the steepness of the CO2 and O2 expirogram plotted against expired volume suggested a contribution of series in homogeneity due to incomplete gas mixing.     

Muscle plasticity: comparison of a 30-Hz burst with 10-Hz continuous stimulation

The changes in the contractile properties induced by a 30-Hz phasic stimulation paradigm were measured and compared with the changes induced by a 10-Hz continuous stimulation paradigm. The study was performed on the tibialis anterior muscles of cats with one paradigm applied to one hindlimb muscle and the other to the contralateral limb. Both hindlimb muscles received the same number of stimuli in a day, making the average stimulation frequency 10 Hz. Two periods of daily stimulation were studied, 8 and 24 h/day. Muscles stimulated at 30 Hz produced greater overall tetanic tension and, during a prolonged stimulation test, exerted a greater mean tension than muscles stimulated at 10 Hz (50 and 32% increase for animals stimulated for 8 and 24 h/day, respectively). Muscle mass was least reduced and fewer pathological abnormalities were observed in the muscles stimulated at 30 Hz. There were no apparent differences in the histochemistry or biochemistry between muscles stimulated at 10 and 30 Hz, which could account for these differences in muscle properties. These results indicate the 30-Hz paradigm may be better suited than 10 Hz continuous stimulation for applications requiring sustained muscle tension such as correction of scoliosis or muscle conditioning for motor prostheses.     

Erythrocyte deformability and lung segmental vascular resistance: effect of hematocrit

We have investigated the role of erythrocyte (RBC) deformability and perfusate viscosity on lung segmental vascular resistance in 12 isolated perfused lungs of 3- to 5-wk-old rabbits. Each lung was perfused alternately with control and formaldehyde-fixed rabbit RBCs at a flow rate of 80 ml.kg-1.min-1, left atrial and airway pressures being 8 and 6 cmH2O, respectively (zone 3). Perfusate RBC concentration was kept constant at 3.2 x 10(6)/mm3 for group I lungs (n = 6) and 7.2 x 10(6)/mm3 for group II lungs (n = 6). In all lungs, we measured pressures in the pulmonary artery and in 20- to 50-microns-diam arterioles and venules with the micropipette servo-null method during both perfusion periods. Compared with control, fixed cells had a 60% decrease in deformability index (i.e., the volume of a dilute solution of RBCs filtered through a 5-microns Nuclepore filter in 1 min). In groups I and II, perfusate viscosity of fixed cells was 15 and 55% greater, respectively, than that of control cells. We found that perfusion with fixed cells in group I lungs did not alter total or segmental vascular pressure drops. However, in group II lungs, perfusion with fixed cells at twice the cell concentration resulted in an increase in total vascular pressure drop, mainly due to an increase in pressure drop in veins (50% of total) and arteries (33%). The relatively small (17%) increase in pressure drop in microvessels was probably due to distension and/or recruitment of capillaries resulting from increased venular pressures.(ABSTRACT TRUNCATED AT 250 WORDS)     

Blood rheology in acute mountain sickness and high-altitude pulmonary edema.

The role of blood rheology in the pathogenesis of acute mountain sickness and high-altitude pulmonary edema was investigated. Twenty-three volunteers, 12 with a history of high-altitude pulmonary edema, were studied at low altitude (490 m) and at 2 h and 18 h after arrival at 4,559 m. Eight subjects remained healthy, seven developed acute mountain sickness, and eight developed high-altitude pulmonary edema. Hematocrit, whole blood viscosity, plasma viscosity, erythrocyte aggregation, and erythrocyte deformability (filtration) were measured. Plasma viscosity and erythrocyte deformability remained unaffected. The hematocrit level was lower 2 h after the arrival at high altitude and higher after 18 h compared with low altitude. The whole blood viscosity changed accordingly. The erythrocyte aggregation was about doubled 18 h after the arrival compared with low-altitude values, which reflects the acute phase reaction. There were, however, no significant differences in any rheological parameters between healthy individuals and subjects with acute mountain sickness or high-altitude pulmonary edema, either before or during the illness. We conclude that rheological abnormalities can be excluded as an initiating event in the development of acute mountain sickness and high-altitude pulmonary edema.     

Advances in bioconversion of anthracycline antibiotics

During the last decade new anthracycline-type structures with potential usefulness in cancer treatment have been supplied both by new microbial strains and by bioconversions of precursor molecules employing cells or enzymes. We highlight recent advances in bioconversion of anthracycline structures with the main focus on late transformations such as are carried out by oxidoreductases.     

Chitosan-elicited synthesis of callose and of coumarin derivatives in parsley cell suspension cultures

In suspension cultured cells of parsley (Petroselinum crispum), chitosan elicited a rapid deposition of the 1,3-ß-glucan callose on the cell wall and a slower formation of coumarins. With cells remaining in conditioned growth medium, fully N-deacetylated chitosans and partially N-acetylated chitosans were about equally active, the potency increased with the degree of polymerization up to several thousand and addition of reduced glutathione increased the sensitivity of the cells. These results indicate common initial events in the induction of callose and coumarin synthesis although two fully independent metabolic pathways are involved. When the cells were suspended in fresh growth medium, less chitosan was required, and fully N-deacetylated chitosan became the best callose elicitor.Abbreviations DP average degree of polymerization - GSH reduced glutathione - PE pachyman equivalents - Pmg Phytophthora megasperma f. sp.glycinea     

Architecture and functional aspects of the distal airways of Antarctic seals with different habits,the Weddell Seal (Leptonychotes weddellii) and the Crabeater Seal (Lobodon carcinophagus)

Summary The lung of the deep diving Weddell Seal is characterized by an unusually well developed periacinar dense collagenous connective tissue, and a thick coat of smooth musculature particularly in the distal bronchioli. Both, collagen and smooth musculature appear to be functionally interrelated, the first serving presumably as site of origin or attachment for the latter. The orientation of the bronchiolar smooth muscle cells is complex: there exists a basic pattern of two crisscrossing helical bundles that wind in opposite direction. In addition, longitudinal bundles are frequent both at the inside and the outside of the muscular coat. Furthermore, more or less complete ringshaped bundles occur as well as groups of muscle fibres running radially into the collagenous tissue of the surroundings of a bronchiolus. This complex architecture presumably allows active adjustment to various physiological needs of the Weddell Seal including as extremes both closing and widening of the bronchiolar lumen. Isometric contractions of the smooth musculature may stiffen the wall of the distal airways while diving. In the Crabeater Seal which dives for shorter durations and by far less deeply than the Weddell Seal, both periacinar collagen and bronchiolar smooth musculature are of similar arrangement, however, occur in considerably reduced amounts. A rich supply of autonomie nerve fibres with abundant varicosities controls the smooth muscle cells, which are interconnected by gap junctions and receive their innervation par distance (visceral type of smooth musculature). The majority of varicosities contains small clear vesicles, as is typical for cholinergic nerves, suggesting a strong parasympathetic influence. Other varicosities are presumably of peptidergic type. Mast cells and epithelial endocrine cells may exert additional influence on the musculature.     

Nuclear Overhauser effect and computational characterization of the beta-spiral of the polypentapeptide of elastin

The structure of the elastin polypentapeptide, poly(VPGVG), was studied by nuclear Overhauser effect experiments using perdeuterated Val1 and Val4 samples under the condition where intermolecular interactions are absent. More extensive interaction was found between the Val1 gamma CH and Pro2 beta CH protons than between the Val4 gamma CH and Pro2 beta CH protons. The Val1 gamma CH3-Pro2 beta CH interaction does not occur within the same pentamer as previously shown experimentally and as expected from steric considerations. The results are incompatible with the presence of a random chain network in poly(VPGVG) at room temperature but are readily explicable in terms of interturn interactions in a beta-spiral structure. More specifically, the results indicate that the beta-spiral conformation with 2.9 pentamers/turn is more prevalent than that with 2.7 pentamers/turn. Using conformations developed by molecular mechanics calculations, molecular dynamics simulations were carried out to compare the relative energies of these two variants of this class of beta-spiral structures. It was found in vacuo that the structure with 2.9 pentamers/turn is indeed more stable than that of 2.7 pentamers/turn by approximately 1 kcal/mole-pentamer.     

The polymorphic marker DXS304 is within 5 centimorgans of the fragile X locus

The fragile X syndrome, which is the most common cause of inherited mental retardation, poses important diagnostic problems for genetic counseling. The development of diagnostic strategies based on DNA analysis has been impaired by the lack of polymorphic markers very close to the disease locus. Here we report that the polymorphic probe U6.2 (locus DXS304) is much closer to the fragile X locus than all the previously reported markers. A recombination fraction of 0.02 between DXS304 and the fragile X locus was estimated by multipoint linkage analysis (confidence interval 0.002 to 0.05). Our data suggest that DXS304 is distal to the fragile X locus. This marker thus represents a major improvement for carrier detection and prenatal diagnosis in fragile X families.