How does canal taper affect root stresses?

AIM: To examine the effect of specific tapers on root stresses and thus vertical root fracture. METHODOLOGY: The effect of taper on root stresses was calculated during simulated warm vertical compaction of gutta-percha in a straight rooted premolar for three tapers (0.04, 0.06 and 0.12 mm mm(-1)) using finite element analysis. Stresses in the dentine were observed whilst the root was filled with three subsequent gutta-percha increments. Each increment was compacted at 10 or 15 N and the gutta-percha cooled down to 37 degrees C. After filling, composite was polymerized in the access space. A functional occlusal load of 50 N was then applied on the buccal cusp incline. The stress distribution in the root during the occlusal loading was compared with the stresses during filling. RESULTS: During filling, the highest stresses were found: (a) at the canal surface; (b) using the smallest taper; (c) in the apical third; and (d) during the first gutta-percha increment. The root stress distribution changed when the functional post-filling load was applied. It generated the highest stresses at the external root surface, with a tensile stress concentration at the lingual surface of the cervical third. Since the stresses during simulated masticatory loading concentrated on the external surface, an increased taper size caused only slightly higher root stress levels. CONCLUSIONS: With increasing taper, root stresses decreased during root filling but tended to increase for masticatory loading. Root fracture originating at the apical third is likely initiated during filling, whilst fracture originating in the cervical portion is likely caused by occlusal loads.

Alpha 1-antitrypsin nonsense mutation associated with a retained truncated protein and reduced mRNA.

alpha 1-Antitrypsin (alpha 1AT) provides the major protection in the lung against neutrophil elastase-mediated proteolysis. Inheritance of alpha 1AT deficiency alleles is associated with an increased risk of emphysema and liver disease. alpha 1AT null alleles cause the total absence of serum alpha 1AT and represent the ultimate in a continuum of alleles associated with alpha 1AT deficiency. The molecular mechanisms responsible for absence of serum alpha 1AT include splicing abnormalities, deletion of alpha 1AT coding exons, and premature stop codons. We identified an Italian individual with asthma, emphysema, and a very low level of serum alpha 1AT. DNA sequencing demonstrated the Mprocida deficiency allele and a novel null allele, QOtrastevere (c654 G-->A, W194Z), a nonsense mutation near the intron 2 (IVS2) splice acceptor site. To determine the molecular basis of QOtrastevere and specifically to evaluate whether this nonsense mutation interfered with mRNA processing by altered splicing, we used a Chinese hamster ovary cell line permanently transfected with QOtrastevere or normal M alpha 1AT with and without IVS2. Northern blot analysis demonstrated that the normal M construct, with or without IVS2, expressed alpha 1AT mRNA of a similar size. The nonsense mutation was associated with moderately reduced alpha 1AT mRNA regardless of the presence or absence of IVS2. Reduction in alpha 1AT mRNA regardless of the opportunity for splicing supports a translational-translocation model as the cause of reduced alpha 1AT mRNA rather than the nuclear scanning model. Pulse-chase studies followed by immunoprecipitation demonstrated an endoplasmic reticulum-retained 31 kDa QOtrastevere alpha 1AT, which was rapidly degraded. Although mRNA content was moderately reduced, retention and rapid intracellular degradation of the truncated form are the major mechanisms for the absence of secreted alpha 1AT.

Regional release and removal of catecholamines and extraneuronal metabolism to metanephrines.

Norepinephrine (NE) and epinephrine (E) are metabolized extraneuronally by catechol-O-methyl-transferase to the metanephrines (MNs), normetanephrine (NMN) and metanephrine (MN). Subjects in this study received infusions of tritium-labeled NE and E. Concentrations of MNs and catecholamines were measured in plasma flowing into and out of the heart, forearm, lungs, kidneys, mesenteric organs (gastrointestinal tract, spleen, and pancreas), liver, and adrenals to examine the regional production of MNs from circulating and locally released catecholamines. NE spillover from mesenteric organs and kidneys accounted for 64% of the spillover from all tissues. There was detectable spillover of E from most extraadrenal tissues, but 91% was from the adrenals. The production of MNs from locally released and circulating catecholamines varied widely among tissues. The liver made the largest contribution to removal of circulating NE (57%) and E (32%) and the largest contribution to the production of NMN (54%) and MN (37%) from metabolism of circulating catecholamines. In all other tissues more NMN was produced from locally released than from circulating NE. Thus, the metabolism of circulating NE was responsible for only 19% of the total production of NMN. An even smaller portion (6%) of plasma MN was derived from metabolism of circulating E. Most plasma MN (91%) was produced within the adrenals, which also provided the largest single source (23%) of NMN. The regional variation in extraneuronal production of MNs indicates considerable heterogeneity in how circulating and locally released catecholamines are handled by different tissues. The substantial contribution of the adrenals to the production of MNs explains the extraordinary sensitivity of these metabolites for the diagnosis of pheochromocytoma.

RNA editing of the coI mRNA throughout the life cycle of Physarum polycephalum.

Editing of RNA via the insertion, deletion or substitution of genetic information affects gene expression in a variety of systems. Previous characterization of the Physarum polycephalum cytochrome c oxidase subunit I (coI) mRNA revealed that both nucleotide insertions and base substitutions occur during the maturation of this mitochondrial message. Both types of editing are known to be developmentally regulated in other systems, including mammals and trypanosomatids. Here we show that the coI mRNA present in Physarum mitochondria is edited via specific nucleotide insertions and C to U conversions at every stage of the life cycle. Primer extension sequencing of the RNA indicates that this editing is both accurate and efficient. Using a sensitive RT-PCR assay to monitor the extent of editing at individual sites of C insertion, we estimate that greater than 98% of the steady-state amount of coI mRNA is edited throughout the Physarum developmental cycle.

Cardiac noradrenergic function one year following cardiac transplantation.

Controversy exists whether or not cardiac nerves regrow into a human transplanted heart. The present study examined cardiac noradrenergic function one year following cardiac transplantation. Eight male cardiac transplant recipients having standard triple immunosuppressive treatment were catheterized diagnostically one year after heart transplantation. They had normalized cardiac hemodynamics and showed no histological rejection in biopsies. A second study group, with intact cardiac innervation, consisted of 19 patients with stable angina pectoris class I to III. Cardiac sympathetic nerve activity was assessed by measurements of cardiac noradrenaline (NA) extraction and spillover, using infusion of tritium-labelled NA (3H-NA). To further characterize cardiac noradrenergic function (synthesis and metabolism) arterial and coronary venous plasma concentrations of the NA precursor, dihydroxyphenylalanine (DOPA), the dopamine metabolite, dihydroxyphenylacetic acid (DOPAC), and the intra-neuronal NA metabolite, dihydroxyphenylglycol (DHPG), were also examined. In transplant recipients, cardiac sympathetic function was also examined before and during supine bicycle exercise and after administration of desipramine to block neuronal uptake. Significant dilution of 3H-NA with endogenous NA from arterial to coronary venous plasma in cardiac transplant patients indicated detectable spillover of NA into plasma from transplanted hearts. However, cardiac spillover of NA in heart transplant patients was only a quarter of that observed in angina patients. Also, transplanted hearts showed no production of DOPA, DOPAC, DHPG or 3H-labelled DHPG, whereas there were positive arterial-venous plasma gradients in all these catechols across the hearts of angina patients. Cardiac fractional extraction of NA was 74% in the angina patients, but only 13% in transplant patients. In transplant patients, cardiac spillover of NA and extraction of 3H-NA were not affected by desipramine or exercise. The present study shows little evidence of any functional activity of cardiac sympathetic nerves in the transplanted heart, as assessed by biochemical indices of release, reuptake, metabolism and synthesis of NA. This argues against cardiac reinnervation of functional importance, at least within the first postoperative year.