Thoracoabdominal restriction in supine men: CT and lung function measurements

Thoracoabdominal restriction was brought on by means of a corset, and the subsequent effects on thoracic dimensions and lung tissue were studied by computerized tomography (CT) and by various lung function tests in supine healthy volunteers (mean age 30 yr). Restriction caused reductions in total lung capacity (helium equilibration) from mean 6.84 to 4.80 liters, in functional residual capacity (FRC) from 2.65 to 2.08 liters, and in vital capacity from 5.16 to 3.45 liters. Closing capacity (single-breath N2 washout) fell from 2.42 to 1.88 liters, thus matching the reduction in FRC. The static pressure-lung volume curve was shifted to the right by 1.5 cmH2O at 50% of total lung capacity. However, no change in the slope of the curve was observed. The diaphragm was moved cranially by 1.2 cm, and the thoracic cross-sectional area was reduced by a mean 32 cm2 at a level just above the diaphragm. No changes in the lung tissue were seen on CT scanning. Gas exchange, as assessed by multiple inert gas elimination technique and arterial blood gas analysis, was unaffected by restriction. It is concluded that in supine subjects, thoracoabdominal restriction that reduces FRC by 0.6 liter is not accompanied by atelectasis (normal CT scan). In this respect the result differs from that found in anesthetized supine subjects who show the same fall in FRC and atelectasis in dependent lung regions.     

Three C. elegans Rac proteins and several alternative Rac regulators control axon guidance, cell migration and apoptotic cell phagocytosis.

The Caenorhabditis elegans genome contains three rac-like genes, ced-10, mig-2, and rac-2. We report that ced-10, mig-2 and rac-2 act redundantly in axon pathfinding: inactivating one gene had little effect, but inactivating two or more genes perturbed both axon outgrowth and guidance. mig-2 and ced-10 also have redundant functions in some cell migrations. By contrast, ced-10 is uniquely required for cell-corpse phagocytosis, and mig-2 and rac-2 have only subtle roles in this process. Rac activators are also used differentially. The UNC-73 Trio Rac GTP exchange factor affected all Rac pathways in axon pathfinding and cell migration but did not affect cell-corpse phagocytosis. CED-5 DOCK180, which acts with CED-10 Rac in cell-corpse phagocytosis, acted with MIG-2 but not CED-10 in axon pathfinding. Thus, distinct regulatory proteins modulate Rac activation and function in different developmental processes.     

Localization of ornithine decarboxylase in the chick embryo during organogenesis

Summary The localization of ornithine decarboxylase (ODC), a key enzyme in polyamine biosynthesis and thus in cell growth, was determined in the 4.5-day-old chick embryo, using two independent methods of analysis. ODC protein was identified by indirect immunofluorescence with a monospecific ODC antibody, and catalytically active ODC was identified by autoradiography with -(5-³H) difluoromethylornithine. Both methods revealed a basically similar distribution of ODC within the embryo. Among the organs, the brain exhibited the highest ODC levels. ODC levels were also high in spinal cord, mesonephric tubules and heart. Similar levels, but confined to limited areas, were found in liver tissue, head mesenchyme, and the oral and pharyngeal regions. Organs that exhibited high ODC levels are all engaged in rapid growth, as well as in extensive tissue remodeling and differentiation.     

Diamide inhibits pulmonary vasoconstriction induced by hypoxia or prostaglandin F2 alpha

Diamide oxidizes glutathione and other cellular sulfhydryl groups. It decreases calcium ATPase activity and alters mitochondrial calcium flux, probably as a result of the sulfhydryl oxidation. We examined the effect of diamide (5 mg/kg, iv) on pulmonary vascular reactivity in 12 anesthetized dogs. Diamide reversed the pulmonary vasoconstriction caused by hypoxia in seven dogs (control delta PVR + 2.5 +/- 0.6 mm Hg/liter/min; postdiamide delta PVR - 0.1 +/- 0.4 mm Hg/liter/min; P less than 0.01). The pulmonary pressor response to prostaglandin F2 alpha (5 micrograms/kg/min, iv) was also reduced (control delta PVR + 3.8 +/- 0.5 mm Hg/liter/min; postdiamide delta PVR + 1.1 +/- 0.7 mm Hg/liter/min; P less than 0.01). However, in a further five dogs, diamide had only a small effect on the pulmonary vasoconstriction caused by angiotensin II, while the pressor response to hypoxia was again inhibited. The mechanism by which diamide reverses pulmonary vasoconstriction is not certain but the effect is rapid, consistent, and reversible. Because the intravenous infusion of diamide does not produce systemic hypotension, during its period of action on the pulmonary vasculature, unlike the drugs currently available for the clinical treatment of pulmonary hypertension, further studies of its mechanism of action are indicated.     

Characterization of the murine corticosteroid binding globulin: variations between mammalian forms

Corticosteroid binding globulin (CGB) from term-pregnant mouse serum was isolated and characterized by peptide analysis after treatment with CNBr and Lys-specific protease, respectively. Amino acid sequence analysis of six segments, covering 189 of 383 positions in different regions of the protein, showed unexpectedly low overall homology (60%) to the indirectly deduced human amino acid sequence previously reported. However, some segments displayed a greater resemblance to their human counterparts. Differences were observed in at least two of six potential glycosylation sites. The nature of electrophoretic CBG variants and their immunological properties are described.     

Cyclic nucleotide phosphodiesterase. Partial purification and characterization of a high affinity enzyme activity from human lung tissue.

Part of the soluble cyclic nucleotide phosphodiesterase activity of crude human lung tissue can be attributed to a thermosensitive (37 degrees) enzyme with a high apparent affinity for both adenosine 3':5'-monophosphate (cyclic AMP) and guanosine 3':5'-monophosphate (cyclic GMP). The enzyme can be partially purified by DEAE-Sephadex chromatography. In the presence of 0.1 mM EDTA or ethylene glycol bis(beta-aminoethyl ether)N,N'-tetraacetic acid (EGTA), it is eluted from the column immediately before a cyclic GMP-specific phosphodiesterase, but in the presence of 0.2 mM Ca2+, the elution follows that of the cyclic GMP-specific enzyme. The two forms of the nonspecific phosphodiesterase activity are referred to as DEAD-Sephadex Fractions Ia and Ic, respectively. Their apparent molecular weights, recorded at gel filtration, vary with different preparations from 230,000 to 150,000. Occasionally, corresponding recordings for main peaks of activity also cluster round the values 120,000, 105,000, and 78,000. The enzymatic properties of Fractions Ia and Ic closely resemble each other. The enzyme activity is blocked by EDTA, partially inhibited in the presence of 1,10-phenanthroline, but only slightly affected by EGTA. The inhibitory effect of EDTA can be overcome by Mg2+ and Mn2+ and that of 1,10-phenanthroline, in part, by Zn2+; this cation in itself is inhibitory at millimolar concentrations. With submicromolar substrate concentrations, the activity of either fraction obeys linear kinetics displaying an apparent Km of approximately 0.4 micron for both substrates. Reciprocal inhibition experiments suggest that hydrolysis of both cyclic AMP and cyclic GMP is performed by the same active site. Examination of the activity using extended substrate concentration ranges indicates nonlinear kinetics; Hill plots of such data also show nonlinear curvature. The activity is inhibited by micromolar concentrations of inosine 3':5'-monophosphate (cyclic IMP), 3-isobutyl-1-methylxanthine, papervine, and some antiallergic agents. Theophylline and disodium cromoglycate are less potent inhibitors. Inhibition of activity by Lubrol PX follows a biphasic dose response curve. The activity of Fraction Ia can be enhanced 2- to 3-fold by a Ca2+-dependent activator prepared from lung tissue, whose action is counteracted by chlorpromazine, and by lysophosphatidylcholine. It is initially enhanced but subsequently decreased at exposure to trypsin. Fraction Ic is less prone to activation by these agents. The results indicate that the present activity represents an enzyme form that differs from three previously described phosphodiesterases of human lung tissue. It is apparently related to, but also shows distinct differences from the Ca2+-dependent enzyme(s) of brain and heart tissue.     

Pseudomonas 3 beta-hydroxysteroid dehydrogenase. Primary structure and relationships to other steroid dehydrogenases

The 3 beta-hydroxysteroid dehydrogenase of Pseudomonas testosteroni commercially available was purified by an FPLC step and submitted to sequence determination by peptide analysis. The structure obtained reveals a 253-residue polypeptide chain, with an N-terminal, free alpha-amino group, and a low cysteine content. Comparisons with other hydroxysteroid dehydrogenases recently characterized reveal distant similarities with prokaryotic and, to some extent, also eukaryotic forms of separate specificities. Residue identities with a Streptomyces 20 beta-hydroxysteroid dehydrogenase are 35% and distributed over the entire molecule, whereas residue identities with the mammalian 17 beta-hydroxysteroid dehydrogenase only constitute 20%, and are essentially limited to the N-terminal and central parts, Nevertheless, all these enzymes exhibit a conserved tyrosine residue (position 151 in the present enzyme) noted as possibly having a functional role in some members of this protein family. Combined, the results establish the prokaryotic 3 beta-hydroxysteroid dehydrogenase as belonging to the family of short-chain alcohol dehydrogenases, reveal that the hydroxysteroid dehydrogenases are no more closely related than dehydrogenases with other enzyme activities within the family (e.g. glucose, ribitol, hydroxyprostaglandin dehydrogenases), show several of the mammalian hydroxysteroid dehydrogenases to have subunits of longer size with different patterns of similarity than those of the prokaryotic family members characterized, and define important segments of the coenzyme-binding region for this enzyme group.     

Influences of gastro-intestinal polypeptides and glucose on glucagon secretion induced by cholinergic stimulation

Glucagon secretion from the endocrine pancreas is known to be enhanced by cholinergic stimulation. It has previously been described that vasoactive intestinal polypeptide (VIP) is a potent potentiator of this cholinergically induced glucagon secretion. In the present study, the effects of several gastro-entero-pancreatic polypeptides and glucose on glucagon secretion induced by the cholinergic agonist carbachol were investigated in vivo in the mouse. Carbachol was injected i.v. and it stimulated glucagon secretion. The polypeptides neurotensin and gastric inhibitory polypeptide (GIP) were both found to potentiate the carbachol-induced glucagon secretion, whereas substance P, pancreatic polypeptide, and two different molecular variants of cholecystokinin, CCK-8 and CCK-39, were without effect on cholinergically induced glucagon secretion. Neither of these polypeptides had any influence on basal glucagon secretion when tested over a wide dose range. Somatostatin and glucose both markedly inhibited carbachol-induced glucagon secretion. In conclusion: carbachol is a potent stimulator of glucagon secretion. This cholinergically induced glucagon secretion can be modified by several gastro-entero-pancreatic hormones influencing the release process both in potentiating and inhibiting direction. The physiological relevance of these interactions remains to be further investigated.