Hydrophilic solute transport across rat alveolar epithelium

Diffusional fluxes of a series of hydrophilic nonelectrolytes (molecular radii ranging from 0.15 to 0.57 nm) were measured across the alveolocapillary barrier in the isolated perfused fluid-filled rat lung. Radiolabeled solutes were lavaged into the distal air spaces of isolated Ringer-perfused lungs, and apparent permeability-surface area products were calculated from the rates of isotope appearance in the recirculating perfusate. These data were used to estimate theoretical equivalent pore radii in the alveolar epithelium, with the assumption of diffusive flow through water-filled cylindrical pores. The alveolar epithelium is best characterized by two pore populations, with small pores (radius 0.5 nm) occupying 98.7% of total pore area and larger pores (radius 3.4 nm) occupying 1.3% of total pore area. Net water flow out of the alveolar space was measured by including an impermeant solute (dextran) in the lavage fluid and measuring its concentration in the alveolar space as a function of time. Under control conditions, net water flow averaged 167 nl/s. When 24 microM terbutaline was added to the perfusate, net water flow increased significantly to 350 nl/s (P less than 0.001). Terbutaline had no effect on the fluxes of either glycerol (which traverses the small pore pathway) or sucrose (which traverses the large pore pathway). These findings indicate that the intact mammalian alveolar epithelium is complex and highly resistant to the flow of solutes and water.     

Calcitonin and CGRP block bombesin- and substance P-induced increases in airway tone

Calcitonin gene-related peptide (CGRP) and calcitonin (C) are two peptides that are cocontained and probably coreleased with the potent bronchocontrictors, bombesin (B) and substance P (SP), within the lung. Although CGRP and C have a wide intrapulmonary distribution, their actions have not been well defined. By the use of a computerized lung mechanics analyzer, changes in response to 10-min infusions of these agents were measured in spontaneously breathing, anesthetized guinea pigs. Infusion of 0.3 nmol.kg-1.min-1 CGRP and 2 nmol.kg-1.min-1 C caused little change in lung mechanics. Infusion of 0.06 nmol.kg-1.min-1 B and 0.3 nmol.kg-1.min-1 SP caused a marked increase in inspiratory, expiratory, and total pulmonary resistance (RT), from base-line values (P less than 0.02), with a maximal effect at 10 min postinfusion (PI) [RT = 326 +/- 20% (SE) (B), 490 +/- 73% (SP)]. Coinfusion of C or CGRP with B or SP at the above concentrations caused a marked reduction in SP - [RT = 189 +/- 28% (C), 142 +/- 16% (CGRP) at 10 min PI] and B - [RT = 157 +/- 18% (C), 158 +/- 10% (CGRP) at 10 min PI] induced changes in resistance (P less than 0.015). The mode of action of C and CGRP is unknown, but these peptides may antagonize the effects of B and SP via autonomic pathways by interfering with B- or SP-induced changes in intracellular calcium concentrations or by increasing intracellular cAMP levels by binding to specific cellular receptors linked to adenylate cyclase.     

Effects of tracheal airway occlusion on hyoid muscle length and upper airway volume

Complex relationships exist among electromyograms (EMGs) of the upper airway muscles, respective changes in muscle length, and upper airway volume. To test the effects of preventing lung inflation on these relationships, recordings were made of EMGs and length changes of the geniohyoid (GH) and sternohyoid (SH) muscles as well as of tidal changes in upper airway volume in eight anesthetized cats. During resting breathing, tracheal airway occlusion tended to increase the inspiratory lengthening of GH and SH. In response to progressive hypercapnia, the GH eventually shortened during inspiration in all animals; the extent of muscle shortening was minimally augmented by airway occlusion despite substantial increases in EMGs. SH lengthened during inspiration in six of eight animals under hypercapnic conditions, and in these cats lengthening was greater during airway occlusion even though EMGs increased. Despite the above effects on SH and GH length, upper airway tidal volume was increased significantly by tracheal occlusion under hypercapnic conditions. These data suggest that the thoracic and upper airway muscle reflex effects of preventing lung inflation during inspiration act antagonistically on hyoid muscle length, but, because of the mechanical arrangement of the hyoid muscles relative to the airway and thorax, they act agonistically to augment tidal changes in upper airway volume. The augmentation of upper airway tidal volume may occur in part as a result of the effects of thoracic movements being passively transmitted through the hyoid muscles.     

Water homeostasis in desert-dwelling horses

This study set out to investigate tolerance of the body water pool to short-term water deprivation in horses and, in particular, to assess whether feral horses from the Namib Desert showed tolerance to dehydration superior to Transvaal. Hydration status was compared in six feral horses from the Namib Desert and in six Boerperd farm horses under conditions of normal hydration and after 72 h of dehydration. Under normal hydration, the two groups did not differ significantly in water intake, plasma sodium and potassium concentrations, plasma osmolality, hematocrit, total plasma protein, body water content, or water turnover (ml.kg-0.82.day-1). The Namib horses were significantly smaller (P less than 0.0001) and turned over 5 liters less water per day than the Boerperd during normal hydration and 4 liters less during dehydration. Increases in plasma sodium concentration after 72 h of dehydration were greater (P less than 0.05) in the Namib horses. It was concluded that horses can easily tolerate water deprivation that results in a 12% reductions in body mass. The feral horses of the Namib desert were not significantly different per unit mass from domestic horses with regard to indexes of total body water content under conditions of normal hydration and after 72 h of dehydration. Their smaller size and, hence, lower water turnover might be mechanisms they use for survival in the Namib Desert.     

Detection and identification ofPodophyllotoxin produced by cell cultures derived from podophyllum hexandrum royle

The phenylpropanoid derived lignan podophyllotoxin, occurring inPodophyllum species, is used as a starting compound for the chemical synthesis of the antitumour agents etoposide (VP-16-213) and teniposide (VM-26). At present, the availability of this lignan becomes increasingly limited. As an alternative source, cell cultures originating fromPodophyllum hexandrum Royle were initiated. Analysis of the cell extracts using different HPLC systems as well as TLC, indicated the presence of podophyllotoxin. After prepurification of the extracts by means of ITLC, the identity was confirmed by mass spectrometric analysis. Dark-grown cultures accumulated considerable higher amounts of podophyllotoxin in comparison with the light-grown cultures.     

Interactions between a symmetrical minor groove binding compound and DNA oligonucleotides: 1H and 19F NMR studies

High-resolution NMR techniques (proton and 19F) have been used to study the interactions between several DNA oligonucleotides with varying length of AT base pairs and the synthetic pyrrole-containing compound (P1-F4S-P1), which has properties similar to the DNA minor groove binding drug distamycin A. When this two-fold symmetrical DNA binding molecule is added to the self-complementary DNA oligomers, the resulting complex exhibits an NMR spectrum without any doubling of individual resonances, consistent with a two-fold symmetry of the complex. This is in contrast to all other complexes studied so far. The minimum length of an AT stretch for specific ligand binding is judged to be greater than 4 base pairs. Inter-molecular proton nuclear Overhauser effects between the ligand molecule and a DNA dodecamer d(CGCAAATTTGCG) provide evidence that P1-F4S-P1 binds DNA in the minor groove and interacts with the middle AT base pairs. The presence of a specific interaction between P1-F4S-P1 and DNA is conclusively demonstrated by 19F NMR studies, in which four previously chemically equivalent fluorine nuclei in the free molecule become two non-equivalent pairs (yielding an AB quartet pattern) upon the binding of P1-F4S-P1 to DNA duplex. A sequence-dependent binding behavior of P1-F4S-P1 is evident by comparing the 19F NMR spectra of the complexes between P1-F4S-P1 and two different but related DNA dodecamers, d(CGCAAATTTGCG) and d(CGCTTTAAAGCG). P1-F4S-P1 binds more strongly to the former dodecamer with an association constant of approximately 1 X 10(3) M-1.     

Definition of subchromosomal intervals around the myotonic dystrophy gene region at 19q

The localization to 19q of the gene causing myotonic dystrophy (DM) has been defined more precisely by refinement of the physical location of several linked markers. A somatic cell hybrid mapping panel from cells with t(1;19), t(12;19), and t(X;19) translocation products was constructed to define five different intervals across 19q. In addition, we have derived a series of cell hybrids by irradiation of a der(19)-only hybrid to further subdivide the cen-q13.1 region. Using an array of 36 cloned genes, anonymous DNAs, and enzyme markers, we have tested the location of the panel breakpoints and refined the regional assignment of several of these markers. All markers tightly linked to DM are localized mainly within 19q13.2, thus suggesting that the DM gene is also close to this region.     

Analysis of molecular deletions with cDNA probes in patients with Duchenne and Becker muscular dystrophies

In the course of a systematic survey of DMD and BMD patients with intronic probes and with cDNA probes covering three-fourths of the coding sequence, 45 molecular deletions within the DMD gene were investigated. Forty-two percent of the breakpoints were located in the intronic sequence containing probe P20, whereas the other deletions were widespread around the more proximal part of the gene. Most of the BMD deletions were in the P20 region. Pulsed field gel electrophoresis was used to determine the size of some deletions and allowed us to estimate the physical distance between the intronic probes JBir and P20. The reading frame was checked in 11 cases with proximal deletions and found to be disrupted in 6 of 7 DMD patients, in 1 intermediate case, and, unexpectedly, in 3 BMD patients.