Surgical placement of rectus sheath catheters in a cadaveric cystectomy model

Introduction Surgically inserted rectus sheath catheters (RSCs) are used increasingly for analgesia after cystectomy and other abdominal surgery. Currently, there is little information on the optimal positioning of RSCs to allow maximal spread of local anaesthetic. This study sought to assess the spread of dye injected via RSCs and to highlight the extent of its coverage in a fresh unembalmed cadaveric cystectomy model in order to confirm the nerve endings that are likely to be anaesthetised with RSCs. Methods Four cadavers underwent lower midline incision with limited bladder mobilisation. A RSC was inserted into the eight hemiabdomens. The RSCs were positioned either anterior (n=5) or posterior to the rectus muscle (n=3). Dye was injected down the RSCs to evaluate spread. The eight hemiabdomens were dissected anatomically to determine the surface area of dye spread and nerve root involvement. Results The mean surface area of dye spread with anteriorly placed RSCs was 30.6cm² anterior and 25.9cm² posterior to the rectus muscle. The mean surface area of dye spread with posteriorly placed RSCs was 11.3cm² anterior and 37.3cm² posterior to the rectus muscle. The mean number of nerve roots stained with anteriorly and posteriorly placed RSCs was 3.8 and 2.7 respectively. Subcutaneous spread of dye was seen with one anterior RSC insertion. Peritoneal spread was seen with one anteriorly positioned RSC. Conclusions This study has demonstrated efficient nerve root infiltration with anteriorly and posteriorly positioned RSCs. It appears that dye spreads between the fibres of the rectus muscle rather than out laterally to the nerve roots when spreading from its initial compartment.

Epidural distribution of dye administered via an epidural catheter in a porcine model

BACKGROUND

Local anaesthetics are commonly delivered to the epidural space by either intermittent bolus or continuous infusion. While these methods have been investigated in terms of analgesia and total dose administered, they have not been compared in terms of their effect on the spread of injectate within the epidural space. This animal study compared the spread of dye delivered to the epidural space in a porcine model by either bolus or infusion.

METHODS

After ethical approval, epidural catheters were placed at three vertebral levels in seven anaesthetized pigs. Aqueous dye (1 ml) was injected into the catheter as a bolus, or as an infusion over 30 min. Animals were euthanized at the end of the study and necropsy performed immediately to quantify the extent of dye spread.

RESULTS

In seven animals, 20 catheters were successfully placed in the epidural space. The mean (sd) extent of dye spread was 8.9 (2.6) cm in the infusion group compared with 15.2 (2.7) cm in the bolus group (P<0.001). Segmental spread was significantly greater in the bolus group compared with the infusion group (P<0.01).

CONCLUSION

In the porcine epidural model, spread of one ml of epidural dye solution is more extensive after a single bolus compared with short term infusion.

A Triangular Iron(III) Complex Potentially Relevant to Iron(III)-Binding Sites in Ferreascidin

An asymmetric triangular Fe(III) complex has been synthesized by an unusual Fe(II) -promoted activation of salicylaldoxime. Formation of the ligand 2-(bis(salicylideneamino)methyl)phenol in situ is believed to occur through the reductive deoximation of salicylaldoxime by ferrous ions. The trinuclear ferric complex has been characterized on the basis of elemental analysis, IR, variable-temperature magnetic susceptibility, and EPR and Mössbauer spectroscopies. The molecular structure established by X-ray diffraction consists of a trinuclear structure with a [Fe3 (μ3 -O)(μ2 -OPh)](6+) core. Two iron ions are in a distorted octahedral environment having FeN2 O4 coordination spheres, and the five-coordinated third iron ion, with an FeNO4 coordination sphere, is in a trigonal bipyramidal environment. The magnetic susceptibility measurements revealed an St = 5/2 ground state with the antiparallel exchange interactions J = - 34.3 cm(-1) , J' = - 4.7 cm(-1) , and D = - 0.90 cm(-1) . The EPR results are consistent with a ground state of S = 5/2 together with a negative D5/2 value. The Mössbauer isomer shifts together with the quadrupole splitting also provide evidence for the high-spin state of the three ferric sites. Magnetic Mössbauer spectra lead to the conclusion that the internal magnetic fields possibly lie in the plane of the three ferric ions.

Taxa distribution and RAPD markers indicate different origin and regional differentiation of hybrids in the invasive Fallopia complex in central-western Europe

Interspecific hybridization can be a driving force for evolutionary processes during plant invasions, by increasing genetic variation and creating novel gene combinations, thereby promoting genetic differentiation among populations of invasive species in the introduced range. We examined regional genetic structure in the invasive Fallopia complex, consisting of F. japonica var. japonica, F. sachalinensis and their hybrid F. x bohemica, in seven regions in Germany and Switzerland using RAPD analysis and flow cytometry. All individuals identified as F. japonica var. japonica had the same RAPD phenotype, while F. sachalinensis (11 RAPD phenotypes for 11 sampled individuals) and F. x bohemica (24 RAPD phenotypes for 32 sampled individuals) showed high genotypic diversity. Bayesian cluster analysis revealed three distinct genetic clusters. The majority of F. x bohemica individuals were assigned to a unique genetic cluster that differed from those of the parental species, while the other F. x bohemica individuals had different degrees of admixture to the three genetic clusters. At the regional scale, the occurrence of male-fertile F. sachalinensis coincided with the distribution of F. x bohemica plants showing a high percentage of assignment to both parental species, suggesting that they originated from hybridization between the parental species. In contrast, in regions where male-fertile F. sachalinensis were absent, F. x bohemica belonged to the non-admixed genetic group, indicating multiple introductions of hybrids or sexual reproduction among hybrids. We also found regional differentiation in the gene pool of F. x bohemica, with individuals within the same region more similar to each other than to individuals from different regions.

Rapid development of severe end-organ damage in C57BL/6 mice by combining DOCA salt and angiotensin II

The C57BL/6 mouse strain serves as the genetic background of many transgenic and gene knockout models; however, this strain appears to be resistant to hypertension-induced renal injury. We developed a new model of hypertensive end-organ damage in C57BL/6 mice by combining deoxycorticosterone acetate (DOCA) and salt with angiotensin II infusion. The systolic blood pressure (SBP) was significantly elevated in DOCA salt-angiotensin II mice compared to control mice or mice treated individually with DOCA salt or angiotensin II. Hypertensive glomerular damage, increased expression of profibrotic and inflammatory genes, albuminuria, tubular casts, increased plasma cholesterol, cardiac hypertrophy, and fibrosis were found in mice treated with DOCA salt-angiotensin II. The SBP in the angiotensin II-infused group was further increased by increasing the infusion rate; only mild injury was observed in these mice, suggesting that blood pressure was not a causal factor. Removal of DOCA and the angiotensin pump lowered blood pressure to normal; however, albuminuria along with the glomerular and cardiac damage did not completely resolve. Our study describes a new model of hypertensive end-organ damage and repair in C57BL/6 mice.

Antihypertensive therapy upregulates renin and (pro)renin receptor in the clipped kidney of Goldblatt hypertensive rats

Recently, a (pro)renin receptor has been identified which mediates profibrotic effects independent of angiotensin II. Because antihypertensive therapy induces renal injury in the clipped kidney of two kidney-1-clip hypertensive rats, we examined the regulation of renin and the (pro)renin receptor in this model. Hypertensive Goldblatt rats were treated with increasing doses of the vasopeptidase inhibitor AVE 7688 after which the plasma renin and prorenin as well as the renal renin and (pro)renin receptor expression were measured. The vasopeptidase inhibitor dose-dependently lowered blood pressure, which was associated with a massive increase in plasma prorenin and renin as well as increased renal renin expression. The (pro)renin receptor was upregulated in the clipped kidney of the Goldblatt rat indicating a parallel upregulation of renin and its receptor in vivo. Immunohistochemistry showed a redistribution of renin upstream from the glomerulus in preglomerular vessels and renin staining in tubular cells. Expression of the (pro)renin receptor was increased in the vessels and tubules. This upregulation was associated with thickening of renin-positive vessels and tubulointerstitial damage. We propose that renin and the (pro)renin receptor may play a profibrotic role in the clipped kidney of Goldblatt rats treated for hypertension.

Antihypertensive therapy induces compartment-specific chemokine expression and a Th1 immune response in the clipped kidney of Goldblatt hypertensive rats

The present study examined the pathogenesis of interstitial inflammation and fibrosis in antihypertensively treated rats with two-kidney, one-clip hypertension. Hypertensive rats were randomized into four groups: no treatment and moderate, intermediate, and intensified lowering of blood pressure with increasing doses of a vasopeptidase inhibitor for 6 wk. The vasopeptidase inhibitor dose dependently lowered blood pressure. The tubulointerstitial damage was accompanied by a diffuse infiltration of mononuclear cells and circumscript mononuclear inflammatory cell cluster formation consisting mainly of T cells and to a lesser degree of macrophages and B cells. Real-time PCR analyses showed a dose-dependent induction of MCP-1 and the Th1-type chemokines IP10 and Mig as well as their receptor CXCR3 and the Th1 cytokine IFN-γ. In situ hybridization and laser microdissection revealed a strong expression of these Th1-associated transcripts in the clusters and, in the case of MCP-1, also diffusely in the interstitium. The inflammation was accompanied by the appearance of myofibroblasts and synthesis of the fibrogenic factor plasminogen activator inhibitor-1 as well as the collagenase matrix metalloproteinase-2, leading to collagen I upregulation and interstitial scarring. No inflammation or fibrosis was found in normotensive rats treated with the vasopeptidase inhibitor. The renal injury in the clipped kidney is accompanied by compartment-specific chemokine expression and cell cluster formation of Th1 specificity associated with upregulation of fibrogenic proteins and matrix metalloproteinases. These findings suggest that the Th1 chemokines IP10 and Mig as well as their receptor CXCR3 are potential targets for therapeutic interventions in ischemic nephropathy.

Clinical care of gambling disorders: training, experience, and competence among VHA psychologists

Problem gambling is a common, highly destructive disorder which is often overlooked by clinicians. Levels of clinical training, clinical experience, and professional competence for providing clinical services for problem gambling were examined in a survey of 181 clinical psychologists working in the Veterans Healthcare Administration (VHA). The results suggest that the majority of clinical psychologists have little or no formal training and little or no past or current clinical experience in the treatment of disordered gambling, nor do they see themselves as competent to evaluate or treat patients with disordered gambling. Most have not referred patients for treatment of problem gambling and do not know of a competent provider to whom they can refer. There is an identifiable subgroup, representing 9% of respondents, who do have more training, provide services, and see themselves as competent to provide care for patients with problem gambling. The amount of formal training is positively correlated with care provided and self-ratings of competence. Despite the lack of training and experience, most respondents expressed interest in receiving additional training. These data suggest that to improve rates of diagnosis and treatment of patients with problem gambling in mental health settings, additional training needs to be made available for mental health providers as a group, with specialized training for clinicians interested in specializing in this area.

IscA, an alternate scaffold for Fe-S cluster biosynthesis

An IscA homologue within the nif regulon of Azotobacter vinelandii, designated (Nif)IscA, was expressed in Escherichia coli and purified to homogeneity. Purified (Nif)IscA was found to be a homodimer of 11-kDa subunits that contained no metal centers or other prosthetic groups in its as-isolated form. Possible roles for (Nif)IscA in Fe-S cluster biosynthesis were assessed by investigating the ability to bind iron and to assemble Fe-S clusters in a NifS-directed process, as monitored by the combination of UV-vis absorption, Mössbauer, resonance Raman, variable-temperature magnetic circular dichroism, and EPR spectroscopies. Although (Nif)IscA was found to bind ferrous ion in a tetrahedral, predominantly cysteinyl-ligated coordination environment, the low-binding affinity argues against a specific role as a metallochaperone for the delivery of ferrous ion to other Fe-S cluster assembly proteins. Rather, a role for (Nif)IscA as an alternate scaffold protein for Fe-S cluster biosynthesis is proposed, based on the NifS-directed assembly of approximately one labile [4Fe-4S](2+) cluster per (Nif)IscA homodimer, via a transient [2Fe-2S](2+) cluster intermediate. The cluster assembly process was monitored temporally using UV-vis absorption and Mössbauer spectroscopy, and the intermediate [2Fe-2S](2+)-containing species was additionally characterized by resonance Raman spectroscopy. The Mössbauer and resonance Raman properties of the [2Fe-2S](2+) center are consistent with complete cysteinyl ligation. The presence of three conserved cysteine residues in all IscA proteins and the observed cluster stoichiometry of approximately one [2Fe-2S](2+) or one [4Fe-4S](2+) per homodimer suggest that both cluster types are subunit bridging. In addition, (Nif)IscA was shown to couple delivery of iron and sulfur by using ferrous ion to reduce sulfane sulfur. The ability of Fe-S scaffold proteins to couple the delivery of these two toxic and reactive Fe-S cluster precursors is likely to be important for minimizing the cellular concentrations of free ferrous and sulfide ions. On the basis of the spectroscopic and analytical results, mechanistic schemes for NifS-directed cluster assembly on (Nif)IscA are proposed. It is proposed that the IscA family of proteins provide alternative scaffolds to the NifU and IscU proteins for mediating nif-specific and general Fe-S cluster assembly.

Effects of disability compensation on participation in and outcomes of vocational rehabilitation

OBJECTIVE

The authors sought to determine the relationship between receipt of disability compensation and participants' success in a vocational rehabilitation program.

METHODS

Administrative data for 22,515 individuals who participated in the Veterans Health Administration compensated work therapy program between 1993 and 1998 were analyzed. Six dependent variables were compared between participants who were receiving disability compensation and those who were not: duration of participation in compensated work therapy, number of hours worked per week, mean hourly earnings, total income from compensated work therapy, dropout rate, and competitive employment status at discharge. Regression equations were determined for each dependent variable to assess associations with the degree of disability, the amount of disability compensation, and the type of compensation program.

RESULTS

Participants who were receiving disability benefits worked fewer hours in compensated work therapy each week, earned less income, had a higher dropout rate, and were less likely to be competitively employed at discharge. The amount of compensation and the type of program were modestly but significantly associated with participation in compensated work therapy and with outcome.

CONCLUSIONS

Unintended effects of disability compensation programs discourage full participation in vocational rehabilitation and result in poorer rehabilitation outcomes.

Rational reprogramming of the R2 subunit of Escherichia coli ribonucleotide reductase into a self-hydroxylating monooxygenase

The outcome of O2 activation at the diiron(II) cluster in the R2 subunit of Escherichia coli (class I) ribonucleotide reductase has been rationally altered from the normal tyrosyl radical (Y122*) production to self-hydroxylation of a phenylalanine side-chain by two amino acid substitutions that leave intact the (histidine)2-(carboxylate)4 ligand set characteristic of the diiron-carboxylate family. Iron ligand Asp (D) 84 was replaced with Glu (E), the amino acid found in the cognate position of the structurally similar diiron-carboxylate protein, methane monooxygenase hydroxylase (MMOH). We previously showed that this substitution allows accumulation of a mu-1,2-peroxodiiron(III) intermediate, which does not accumulate in the wild-type (wt) protein and is probably a structural homologue of intermediate P (H(peroxo)) in O2 activation by MMOH. In addition, the near-surface residue Trp (W) 48 was replaced with Phe (F), blocking transfer of the "extra" electron that occurs in wt R2 during formation of the formally Fe(III)Fe(IV) cluster X. Decay of the mu-1,2-peroxodiiron(III) complex in R2-W48F/D84E gives an initial brown product, which contains very little Y122* and which converts very slowly (t1/2 approximately 7 h) upon incubation at 0 degrees C to an intensely purple final product. X-ray crystallographic analysis of the purple product indicates that F208 has undergone epsilon-hydroxylation and the resulting phenol has shifted significantly to become a ligand to Fe2 of the diiron cluster. Resonance Raman (RR) spectra of the purple product generated with 16O2 or 18O2 show appropriate isotopic sensitivity in bands assigned to O-phenyl and Fe-O-phenyl vibrational modes, confirming that the oxygen of the Fe(III)-phenolate species is derived from O2. Chemical analysis, experiments involving interception of the hydroxylating intermediate with exogenous reductant, and Mössbauer and EXAFS characterization of the brown and purple species establish that F208 hydroxylation occurs during decay of the peroxo complex and formation of the initial brown product. The slow transition to the purple Fe(III)-phenolate species is ascribed to a ligand rearrangement in which mu-O2- is lost and the F208-derived phenolate coordinates. The reprogramming to F208 monooxygenase requires both amino acid substitutions, as very little epsilon-hydroxyphenylalanine is formed and pathways leading to Y122* formation predominate in both R2-D84E and R2-W48F.

Influence of a new hydroxyethylstarch preparation (HES 130/0.4) on coagulation in cardiac surgical patients

OBJECTIVE

To compare volume therapy with HES 130/0.4, a new hydroxyethylstarch (HES) solution with a gelatin-based fluid replacement strategy.

DESIGN

Prospective, randomized, safety study.

SETTING

Urban, university-affiliated hospital (single institution).

PARTICIPANTS

Forty-two patients undergoing elective cardiac surgery.

INTERVENTIONS

Patients were prospectively randomized into 2 groups: In group 1 (n = 21), gelatin was given perioperatively for volume support until the 1st postoperative day to keep the central venous pressure (CVP) between 10 and 14 mmHg; in group 2 (n = 21) HES 130/0.4 was administered using the same protocol as in group 1.

MEASUREMENTS AND MAIN RESULTS

Standard coagulation variables and modified thromboelastography (TEG) were used. Using different activators for extrinsic and intrinsic activation and heparin inactivation by heparinase, the onset of coagulation (coagulation time), kinetics of clot formation (clot formation time), and maximum clot firmness were measured. Measurements were performed after induction of anesthesia (T0), at the end of surgery (T1), 4 hours after surgery (T2), and on the morning of the 1st postoperative day (T3). A total of 3310 +/- 810 mL of gelatin and 3070 +/- 570 mL of HES 130/0.4 were used in the 2 groups during the study period. The 2 groups did not differ with regard to postoperative bleeding or in use of packed red blood cells or fresh frozen plasma. Standard coagulation variables were similar between the 2 groups. All TEG variables were within the normal range at baseline. Coagulation time and clot formation time data were significantly elevated after surgery and in the intensive care unit, without showing specific differences between the 2 volume replacement groups. Intrinsic TEG and heparinase TEG clot formation times remained significantly higher until the end of the study period. No differences were seen between HES-treated and gelatin-treated patients.

CONCLUSIONS

Volume replacement with the new HES preparation was as safe as gelatin-based volume replacement with regard to coagulation in cardiac surgical patients. HES 130/0.4 is an alternative plasma substitute to treat volume deficits.

The influence of intravascular volume therapy with a new hydroxyethyl starch preparation (6% HES 130/0.4) on coagulation in patients undergoing major abdominal surgery

A new hydroxyethyl starch (HES) preparation with a mean molecular weight of 130,000 daltons and a degree of substitution of 0.4 shows favorable pharmacokinetic properties. We conducted a study of the influence of the new HES specification on coagulation and compared it with another colloidal intravascular volume replacement regimen using gelatin. According to a prospective, random sequence, 42 patients undergoing major abdominal surgery received either HES 130/0.4 (n = 21) or gelatin (n = 21) until the first postoperative day (POD) to keep central venous pressure between 10 and 14 mm Hg. From arterial blood samples, standard coagulation variables were measured, and modified thrombelastogram (TEG) measurements using different activators were performed. A total of 2830 +/- 350 mL of gelatin and 2430 +/- 310 mL of HES 130/0.4 were administered until the morning of the first POD. The use of allogeneic blood/blood products and standard coagulation variables did not differ significantly between the two groups. After induction of anesthesia, all TEG data for both groups were within normal range. Coagulation time and maximum clot firmness did not change significantly in any TEG measurements during the study period. The kinetics of clot formation (clot formation time) significantly increased immediately after surgery, but without showing significant group differences. On the morning of the first POD, the clot formation time returned to almost normal levels, except for aprotinin-activated TEG(R). We conclude that administration of moderate doses of the new HES 130/0.4 preparation in patients undergoing major abdominal surgery results in similar coagulation alterations as those after using an established gelatin-based volume-replacement regimen.

IMPLICATIONS

We compared the effects of infusion of a new hydroxyethyl starch preparation (6% hydroxyethyl starch; mean molecular weight 130,000 daltons; degree of substitution 0.4) on coagulation with a gelatin-based intravascular volume replacement regimen in patients undergoing major abdominal surgery. After moderate doses of hydroxyethyl starch (2430 +/- 310 mL until the morning of the first postoperative day), coagulation monitoring, including modified thrombelastography, did not show impaired hemostasis.

Neelaredoxin, an iron-binding protein from the syphilis spirochete, Treponema pallidum, is a superoxide reductase

Treponema pallidum, the causative agent of venereal syphilis, is a microaerophilic obligate pathogen of humans. As it disseminates hematogenously and invades a wide range of tissues, T. pallidum presumably must tolerate substantial oxidative stress. Analysis of the T. pallidum genome indicates that the syphilis spirochete lacks most of the iron-binding proteins present in many other bacterial pathogens, including the oxidative defense enzymes superoxide dismutase, catalase, and peroxidase, but does possess an orthologue (TP0823) for neelaredoxin, an enzyme of hyperthermophilic and sulfate-reducing anaerobes shown to possess superoxide reductase activity. To analyze the potential role of neelaredoxin in treponemal oxidative defense, we examined the biochemical, spectroscopic, and antioxidant properties of recombinant T. pallidum neelaredoxin. Neelaredoxin was shown to be expressed in T. pallidum by reverse transcriptase-polymerase chain reaction and Western blot analysis. Recombinant neelaredoxin is a 26-kDa alpha(2) homodimer containing, on average, 0.7 iron atoms/subunit. Mössbauer and EPR analysis of the purified protein indicates that the iron atom exists as a mononuclear center in a mixture of high spin ferrous and ferric oxidation states. The fully oxidized form, obtained by the addition of K(3)(Fe(CN)(6)), exhibits an optical spectrum with absorbances at 280, 320, and 656 nm; the last feature is responsible for the protein's blue color, which disappears upon ascorbate reduction. The fully oxidized protein has a A(280)/A(656) ratio of 10.3. Enzymatic studies revealed that T. pallidum neelaredoxin is able to catalyze a redox equilibrium between superoxide and hydrogen peroxide, a result consistent with it being a superoxide reductase. This finding, the first description of a T. pallidum iron-binding protein, indicates that the syphilis spirochete copes with oxidative stress via a primitive mechanism, which, thus far, has not been described in pathogenic bacteria.

IscU as a scaffold for iron-sulfur cluster biosynthesis: sequential assembly of [2Fe-2S] and [4Fe-4S] clusters in IscU

Iron-sulfur cluster biosynthesis in both prokaryotic and eukaryotic cells is known to be mediated by two highly conserved proteins, termed IscS and IscU in prokaryotes. The homodimeric IscS protein has been shown to be a cysteine desulfurase that catalyzes the reductive conversion of cysteine to alanine and sulfide. In this work, the time course of IscS-mediated Fe-S cluster assembly in IscU was monitored via anaerobic anion exchange chromatography. The nature and properties of the clusters assembled in discrete fractions were assessed via analytical studies together with absorption, resonance Raman, and Mössbauer investigations. The results show sequential cluster assembly with the initial IscU product containing one [2Fe-2S](2+) cluster per dimer converting first to a form containing two [2Fe-2S](2+) clusters per dimer and finally to a form that contains one [4Fe-4S](2+) cluster per dimer. Both the [2Fe-2S](2+) and [4Fe-4S](2+) clusters in IscU are reductively labile and are degraded within minutes upon being exposed to air. On the basis of sequence considerations and spectroscopic studies, the [2Fe-2S](2+) clusters in IscU are shown to have incomplete cysteinyl ligation. In addition, the resonance Raman spectrum of the [4Fe-4S](2+) cluster in IscU is best interpreted in terms of noncysteinyl ligation at a unique Fe site. The ability to assemble both [2Fe-2S](2+) and [4Fe-4S](2+) clusters in IscU supports the proposal that this ubiquitous protein provides a scaffold for IscS-mediated assembly of clusters that are subsequently used for maturation of apo Fe-S proteins.

Evaluation of chemiluminescence immunoassays for detecting thyroglobulin (Tg) and thyroid peroxidase (TPO) autoantibodies using the IMMULITE 2000 system

The chemiluminescence assays for detection of autoantibodies to thyroid peroxidase (TPO) and thyroglobulin (Tg) implemented on the IMMULITE 2000 system (Diagnostic Products Corporation) were evaluated. These were immunometric assays with antigen-coated beads and monoclonal murine anti-IgG antibodies conjugated with alkaline phosphatase. Precision was satisfactory with an intraassay precision of 5.3-5.5% for anti-Tg and 4.8-5.3% for anti-TPO and an interassay precision of 5.7-7.3% for anti-TPO and 5.2-7.5% for anti-Tg. The lower detection limit was determined as 5 IU/ml for anti-TPO and 2.2 IU/ml for anti-Tg. The average dilution linearities of 102% for anti-TPO and 100% for anti-Tg and the average recovery of 80-127% for anti-TPO and 93-112% for anti-Tg were acceptable. The findings of the tests were compared with the systems from Pharmacia & Upjohn, ORGenTec, Roche Diagnostics, Byk Sangtec Diagnostica and BRAHMS Diagnostica. Taking the respective cutoff value into account, concordance was 87-96% for anti-Tg and 87-97% for anti-TPO. Summarizing all results from the different methods revealed a clinical agreement of 95% for anti-TPO and 93% for anti-Tg. A good agreement was found with the IMMULITE anti-TPO and anti-Tg assays, which are closely related as regards method and biochemistry. Regression analysis gave the following results: anti-TPO IMMULITE 2000 vs anti-TPO IMMULITE: anti-TPO IMMULITE 2000 = 0.99 x IMMULITE anti-TPO - 1.43 IU/ml (r = 0.99, n = 144). anti-Tg IMMULITE 2000 vs anti-Tg IMMULITE: anti-Tg IMMULITE 2000 = 0.98 x IMMULITE anti-Tg + 1.63 IU/ml (r = 0.99, n = 86). Further age-dependent normal ranges were evaluated. A higher prevalence of elevated autoantibody titers was found for patients older than 50 years. The rate of elevated antibody titer can be reduced by using an age-dependent reference range: < or = 50 years anti-TPO < 35 IU/ml, anti-Tg < 40 IU/ml and > 50 years anti-TPO < 100 IU/ml, anti-Tg < 80 IU/ml. Further samples from clinically diagnosed Hashimoto's thyroiditis and Graves' disease were investigated. The levels of positive anti-Tg values and anti-TPO values accorded with those stated in the literature and were comparable to those measured with a reference assay. In the tested INSTAND e. V. interlaboratory samples there was high-level accordance with the expected clinical results.

A short Fe-Fe distance in peroxodiferric ferritin: control of Fe substrate versus cofactor decay?

The reaction of oxygen with protein diiron sites is important in bioorganic syntheses and biomineralization. An unusually short Fe-Fe distance of 2.53 angstroms was found in the diiron (mu-1,2 peroxodiferric) intermediate that forms in the early steps of ferritin biomineralization. This distance suggests the presence of a unique triply bridged structure. The Fe-Fe distances in the mu-1, 2 peroxodiferric complexes that were characterized previously are much longer (3.1 to 4.0 angstroms). The 2.53 angstrom Fe-Fe distance requires a small Fe-O-O angle (approximately 106 degrees to 107 degrees). This geometry should favor decay of the peroxodiferric complex by the release of H2O2 and mu-oxo or mu-hydroxo diferric biomineral precursors rather than by oxidation of the organic substrate. Geometrical differences may thus explain how diiron sites can function either as a substrate (in ferritin biomineralization) or as a cofactor (in O2 activation).

Formation of a pterin radical in the reaction of the heme domain of inducible nitric oxide synthase with oxygen

The heme domain (iNOS(heme)) of inducible nitric oxide synthase (NOS) was expressed in Escherichia coli and purified to homogeneity. Rapid freeze-quench (RFQ) EPR was used to monitor the reaction of the reduced iNOS(heme) with oxygen in the presence and absence of substrate. In these reactions, heme oxidation occurs at a rate of approximately 15 s(-)(1) at 4 degrees C. A transient species with a g = 2.0 EPR signal is also observed under these conditions. The spectral properties of the g = 2.0 signal are those of an anisotropic organic radical with S = (1)/(2). Comparison of the EPR spectra obtained when iNOS(heme) is reconstituted with N5-(14)N- and (15)N-substituted tetrahydrobiopterin (H(4)B) shows a hyperfine interaction with the pterin N5 nitrogen and identifies the radical as the one-electron oxidized form (H(3)B.) of the bound H(4)B. Substitution of D(2)O for H(2)O reveals the presence of hyperfine-coupled exchangeable protons in the H(4)B radical. This radical forms at a rate of 15-20 s(-)(1), with a slower decay rate that varies (0.12-0.7 s(-)(1)) depending on the substrate. At 127 ms, H(3)B. accumulates to a maximum of 80% of the total iNOS(heme) concentration in the presence of arginine but only to approximately 2.8% in the presence of NHA. Double-mixing RFQ experiments, where NHA is added after the formation of H(3)B., show that NHA does not react rapidly with H(3)B. and suggest that NHA instead prevents the formation of the H(4)B radical. These data constitute the first direct evidence for an NOS-bound H(3)B. and are most consistent with a role for H(4)B in electron transfer in the NOS reaction.

Biochemical and spectroscopic characterization of overexpressed fuscoredoxin from Escherichia coli

Fuscoredoxin is a unique iron containing protein of yet unknown function originally discovered in the sulfate reducers of the genus Desulfovibrio. It contains two iron-sulfur clusters: a cubane [4Fe-4S] and a mixed oxo- and sulfido-bridged 4Fe cluster of unprecedented structure. The recent determination of the genomic sequence of Escherichia coli (E. coli) has revealed a homologue of fuscoredoxin in this facultative microbe. The presence of this gene in E. coli raises interesting questions regarding the function of fuscoredoxin and whether this gene represents a structural homologue of the better-characterized Desulfovibrio proteins. In order to explore the latter, an overexpression system for the E. coli fuscoredoxin gene was devised. The gene was cloned from genomic DNA by use of the polymerase chain reaction into the expression vector pT7-7 and overexpressed in E. coli BL21(DE3) cells. After two chromatographic steps a good yield of recombinant protein was obtained (approximately 4 mg of pure protein per liter of culture). The purified protein exhibits an optical spectrum characteristic of the homologue from D. desulfuricans, indicating that cofactor assembly was accomplished. Iron analysis indicated that the protein contains circa 8 iron atoms/molecule which were shown by EPR and Mössbauer spectroscopies to be present as two multinuclear clusters, albeit with slightly altered spectroscopic features. A comparison of the primary sequences of fuscoredoxins is presented and differences on cluster coordination modes are discussed on the light of the spectroscopic data.

Compressive and tensile zones in the cement interface of full crowns: a technical note on the concept of resistance

PURPOSE

The objectives of the study were: 1) to map the stresses acting on the cement interface of crown and abutment analogs during loading; and 2) to provide a theoretical basis for the hypothesis that resistance to lateral dislodgment is a function of the distribution of compressive force vectors acting on the cement lute.

MATERIALS AND METHODS

Three-dimensional finite element (FE) meshes of crown and abutment analogs were constructed and loaded in a direction perpendicular to the axes of symmetry of the abutments. Three parameters were investigated: taper (10 degrees and 20 degrees of convergence), abutment substrate (Ni-Cr alloy and dentin), and type of cement (zinc oxide eugenol, zinc phosphate, glass ionomer, and composite resin). The tensile and compressive components of the resulting force systems were plotted along two axes (z: parallel to the axis of symmetry of the crown/abutment complex; and y: perpendicular to z, i.e., parallel to the direction of loading). Von Mises stresses were also generated.

RESULTS

First, it was shown that the restoration's axis of rotation was located inside the abutment cone and was perpendicular to and intersected the axis of symmetry of the crown/abutment complex. Second, stress distribution was dependent on the three parameters investigated. Varying taper led to shifts due mainly to alterations in specimen geometry, whereas the abutment substrate and the cement type had a bearing on the level of the axis of rotation. The smaller the modulus of elasticity of the abutment substrate or the cement lute, the farther apical the location of the axis of rotation.

CONCLUSIONS

Conventional schemes for explaining crown dislodgment in which the restoration rotates around an axis located at the preparation margin should be reassessed. The results of the FE analysis are compatible with the hypothesis that resistance to lateral dislodgment is a function of the distribution of compressive force vectors acting on the cement interface.

The ferroxidase reaction of ferritin reveals a diferric mu-1,2 bridging peroxide intermediate in common with other O2-activating non-heme diiron proteins

Ferritins are ubiquitous proteins that concentrate, store, and detoxify intracellular iron through oxidation of Fe2+ (ferroxidation), followed by translocation and hydrolysis to form a large inorganic mineral core. A series of mutagenesis, kinetics, and spectroscopic studies of ferritin led to the proposal that the oxidation/translocation path involves a diiron protein site. Recent stopped-flow absorption and rapid freeze-quench Mössbauer studies have identified a single peroxodiferric species as the initial transient intermediate formed in recombinant frog M ferritin during rapid ferroxidation [Pereira, S. A., Small, W., Krebs, C., Tavares, P., Edmondson, D. E., Theil, E. C., and Huynh, B. H. (1998) Biochemistry 37, 9871-9876]. To further characterize this transient intermediate and to establish unambiguously the peroxodiferric assignment, rapid freeze-quenching was used to trap the initial intermediate for resonance Raman investigation. Discrete vibrational modes are observed for this intermediate, indicating a single chromophore in a homogeneous state, in agreement with the Mössbauer conclusions. The frequency at 851 cm-1 is assigned as nu(O-O) of the bound peroxide, and the pair of frequencies at 485 and 499 cm-1 is attributed, respectively, to nus and nuas of Fe-O2-Fe. Identification of the chromophore as a micro-1,2 bridged diferric peroxide is provided by the isotope sensitivity of these Raman bands. Similar peroxodiferric intermediates have been detected in a mutant of the R2 subunit of ribonucleotide reductase from Escherichia coli and chemically reduced Delta9 stearoyl-acyl carrier protein desaturase (Delta9D), but in contrast, the ferritin intermediate is trapped from the true reaction pathway of the native protein. Differences in the Raman signatures of these peroxide species are assigned to variations in Fe-O-O-Fe angles and may relate to whether the iron is retained in the catalytic center or released as an oxidized product.

Altered expression of immune-related antigens by neuronophages does not improve neuronal survival after severe lesion of the facial nerve in rats

Injection of Fluoro-Gold (FG) into the whiskerpad muscles of rats yields a permanent retrograde labeling of motoneurons in the facial nucleus. Following subsequent resection of 10 mm of the facial nerve, one-third of the facial motoneurons die and the microglia phagocytize the dead FG-labeled neurons, take up FG, and get labeled in vivo. The resulting identification of all FG-labeled cells allows long-term comparative investigations on the behavior of neuronophages. In this study, we used two groups of rats to test whether the quantified expression of five immune-related antigens by neuronophages was related to quantified decline in neuron number (counts after immunostaining for neuron-specific enolase) 3 to 224 days after resection of the facial nerve. Rats of the first group received standard food and those of the second group, pellets containing 1,000 ppm of the calcium channel blocker nimodipine. Image analysis of the number of FG-containing cells and the number and projection area of immunopositive neuronophages in serial sections for each antigen showed that nimodipine significantly attenuated the immunostaining for CR3, MHC class I, and class II antigens (monoclonal antibodies [MAbs] OX-42, OX-18, and OX-6); enhanced the expression of monocyte-macrophage-specific antigen (MAb ED1); and did not change the expression of rat macrophage differentiation antigen (MAb ED2). The altered expressions, however, had no effect on the loss of motoneurons in the lesioned facial nucleus. We conclude that the degree of expression of immune-related antigens by neuronophages has no influence on the delayed neuronal cell death induced by permanent target deprivation.

Direct spectroscopic and kinetic evidence for the involvement of a peroxodiferric intermediate during the ferroxidase reaction in fast ferritin mineralization

Rapid freeze-quench (RFQ) Mössbauer and stopped-flow absorption spectroscopy were used to monitor the ferritin ferroxidase reaction using recombinant (apo) frog M ferritin; the initial transient ferric species could be trapped by the RFQ method using low iron loading (36 Fe2+/ferritin molecule). Biphasic kinetics of ferroxidation were observed and measured directly by the Mössbauer method; a majority (85%) of the ferrous ions was oxidized at a fast rate of approximately 80 s-1 and the remainder at a much slower rate of approximately 1.7 s-1. In parallel with the fast phase oxidation of the Fe2+ ions, a single transient iron species is formed which exhibits magnetic properties (diamagnetic ground state) and Mössbauer parameters (DeltaEQ = 1.08 +/- 0.03 mm/s and delta = 0.62 +/- 0.02 mm/s) indicative of an antiferromagnetically coupled peroxodiferric complex. The formation and decay rates of this transient diiron species measured by the RFQ Mössbauer method match those of a transient blue species (lambdamax = 650 nm) determined by the stopped-flow absorbance measurement. Thus, the transient colored species is assigned to the same peroxodiferric intermediate. Similar transient colored species have been detected by other investigators in several other fast ferritins (H and M subunit types), such as the human H ferritin and the Escherichia coli ferritin, suggesting a similar mechanism for the ferritin ferroxidase step in all fast ferritins. Peroxodiferric complexes are also formed as early intermediates in the reaction of O2 with the catalytic diiron centers in the hydroxylase component of soluble methane monooxygenase (MMOH) and in the D84E mutant of the R2 subunit of E. coli ribonucleotide reductase. The proposal that a single protein site, with a structure homologous to the diiron centers in MMOH and R2, is involved in the ferritin ferroxidation step is confirmed by the observed kinetics, spectroscopic properties, and purity of the initial peroxodiferric species formed in the frog M ferritin.

Differential expression of calbindin and calmodulin in motoneurons after hypoglossal axotomy

Axotomy induces a profound modification of Ca2+ homeostasis in injured neurons which may lead to neuronal death. Remarkably, after axotomy and resection of the hypoglossal nerve, 65-75% of the hypoglossal motoneurons survive in the long term and this suggests some adaptive mechanisms compensating the massive calcium influx. As potential components of this adaptation, we have examined calmodulin and calbindin-D28k by in situ hybridisation and immunohistochemistry in motoneurons of the rat after hypoglossal nerve transection. Neuronal calbindin mRNA and protein content was low in normal state, transiently increased to 200% of the basal expression at 8 days post-operation (dpo), then declined to normal again until 28 dpo. Calmodulin mRNA was highly expressed in normal hypoglossal motoneurons and remained constant after axotomy. Calmodulin protein immunoreactivity, however, was transiently decreased in axotomised motoneurons suggesting post-transcriptional modification. The upregulation of calbindin expression may facilitate the survival of injured motoneurons.

Spectroscopic characterization of a novel tetranuclear Fe cluster in an iron-sulfur protein isolated from Desulfovibrio desulfuricans

Mossbauer and EPR spectroscopies were used to characterize the Fe clusters in an Fe-S protein isolated from Desulfovibrio desulfuricans (ATCC 27774). This protein was previously thought to contain hexanuclear Fe clusters, but a recent X-ray crystallographic measurement on a similar protein isolated from Desulfovibrio vulgaris showed that the protein contains two tetranuclear clusters, a cubane-type [4Fe-4S] cluster and a mixed-ligand cluster of novel structure [Lindley et al. (1997) Abstract, Chemistry of Metals in Biological Systems, European Research Conference, Tomar, Portugal]. Three protein samples poised at different redox potentials (as-purified, 40 and 320 mV) were investigated. In all three samples, the [4Fe-4S] cluster was found to be present in the diamagnetic 2+ oxidation state and exhibited typical Mossbauer spectra. The novel-structure cluster was found to be redox active. In the 320-mV and as-purified samples, the cluster is at a redox equilibrium between its fully oxidized and one-electron reduced states. In the 40-mV sample, the cluster is in a two-electron reduced state. Distinct spectral components associated with the four Fe sites of cluster 2 in the three oxidation states were identified. The spectroscopic parameters obtained for the Fe sites reflect different ligand environments, making it possible to assign the spectral components to individual Fe sites. In the fully oxidized state, all four iron ions are high-spin ferric and antiferromagnetically coupled to form a diamagnetic S = 0 state. In the one-electron and two-electron reduced states, the reducing electrons were found to localize, consecutively, onto two Fe sites that are rich in oxygen/nitrogen ligands. Based on the X-ray structure and the Mossbauer parameters, attempts could be made to identify the reduced Fe sites. For the two-electron reduced cluster, EPR and Mossbauer data indicate that the cluster is paramagnetic with a nonzero interger spin. For the one-electron reduced cluster, the data suggest a half-integer spin of 9/2. Characteristic fine and hyperfine parameters for all four Fe sites were obtained. Structural implications and the nature of the spin-coupling interactions are discussed.

Axotomy induces transient calbindin D28K immunoreactivity in hypoglossal motoneurons in vivo

Calbindin D28K, an intracellular calcium-binding protein, acts as Ca2+ buffering system in the cytoplasm. By means of this property, calbindin may protect neurons against large fluctuations in free intracellular Ca2+ and, hence, may prevent cell death. Although axotomy causes a massive influx of calcium into the lesioned neurons, resection of the hypoglossal nerve does not induce extensive neuronal cell death in rats. Even several weeks after axotomy, about 70% of the motoneurons survive despite permanent target deprivation. The mechanisms responsible for this remarkable survival rate are unknown. In this study, we have looked at the modification of calbindin immunoreactivity in axotomized hypoglossal motoneurons. In non-axotomized motoneurons, no calbindin is detectable by immunocytochemistry. Axotomy induced an increase of calbindin immunoreactivity in lesioned motoneurons. This increase, visualised by the number of calbindin-immunoreactive neurons extended from 1 day to 28 days. At this time most, but not all, motoneurons located on the side of the lesion were calbindin-positive as shown by retrograde labeling and immunoquenching. From 14 days post operation, calbindin immunoreactivity decreased and reached its basal value after 35 days post operation. At that time, only fibres were still calbindin immunoreactive. Interestingly, calbindin-immunoreactivity was also increased in almost all cell nuclei, compatible with a nuclear regulation. These data are consistent with the hypothesis that, as a reaction to axotomy, motoneurons trigger an increase in calbindin expression which acts as a compensatory Ca(2+)-buffering system, enabling neurons to maintain Ca2+ homeostasis and the survival of many motoneurons after axotomy.

Fetal villosity and microvasculature of the bovine placentome in the second half of gestation

The architecture of the fetal villous tree and its vasculature in the bovine placentome were studied in the second half of gestation using both conventional histology and histology of ink-filled blood vessels. These were compared with corrosion casts of plastic fillings of the vasculature, prepared for scanning electron microscopy. This combination of morphological methods allows perception of the villous tree throughout gestation from broad-conical to tall-conical form where branch ramification occurs mainly at right angles to the stem. The stem villus typically contains a single central artery and several peripheral veins arranged in parallel. The proximal branches to the stem, the intermediate villi, contain a central arteriole and accompanying venules. The distal branches, the terminal villi, enclose capillary convolutions which consist of an afferent arterial capillary limb, capillary loops and efferent venous capillary limbs. Vascular interconnections exist within the terminal villi, as capillaries or venules between the capillary convolutions, serially bridging them in up to 5 places, and as capillary anastomoses between the capillary loops. Coiling and sinusoidal dilatations of these loops develop near the end of gestation. The intraplacentomal rearrangement of villous trees with progressive gestation and their morphological vascular adaptations are discussed in relation to placental function, including the ever increasing need for transplacental substance exchange. This adaptation allows the blood to traverse the shortest possible arterioarteriolar route to the periphery of the trees where exchange takes place. The need for an increasing blood flow stimulates capillary growth and at the same time optimises the blood flow reaching the placental barrier represented by the vessel cast surface. The capillaries also carry the blood back into the very voluminous system of venules and veins where back diffusion may occur. The total volume of terminal villi of bovine placentome, the 'working part' of villous trees, hence distinctly increases with respect to the stem and intermediate villi, the 'supplying part' of the villous tree. In morphological terms the efficiency of the bovine transplacental diffusional exchange is higher than in the closely related 'co-ruminants' sheep and goats and distinctly higher when compared with the human placenta.

Placental vascular corrosion cast studies: a comparison between ruminants and humans

The microvasculature of both the ruminant placentomes of cattle, sheep, and goats and the human placenta were compared, using corrosion casts of blood vessels and scanning electron microscopy. The fetal vascular trees of ruminant and human placenta differ in form and size, which correlates with the degree of ramification; however, their architecture of stem, intermediate, and terminal villi is similar. In the human, the system of serially linked capillary convolutions of terminal villi is longer than that in ruminants. Therefore, in guaranteeing blood flow against flow resistance, the human vessels particularly need a straight course, anastomoses, and sinusoidal dilations. Specifically in the ruminants studied, the venous vessels outweigh the arterial ones by volume and by number. They are suggested to be absorptive for substances metabolized in the zone of the capillary complex. The most extreme interspecies difference relates to the maternal vasculature, which, in contrast to the fetal system, is a closed system in the ruminant septas and an open lacunal intervillous space in the human. Converging and differing morphological vascular phenomena of ruminants and human placenta are discussed in terms of maternofetal exchange related to placental efficiency. In summary, the ruminant placenta, concerning the fetal vascular tree, in many aspects is workable as a model for the human.

Vascular interrelationships of near-term mink placenta: light microscopy combined with scanning electron microscopy of corrosion casts

The microvasculature of the near-term zonary placenta of the mink has been studied using light microscopy and scanning electron microscopy of corrosion casts, prepared from maternal and fetal vessel systems, respectively. The zonary area, most important for placental exchange, includes a characteristic labyrinth. The labyrinth is composed of lobules oriented in a maternal-fetal direction. One maternal stem artery serves as the central axis of a lobule, and about six pairs of fetal stem arteries and stem veins of the chorionic primary villi mark the periphery of the lobule. Viewed from the fetal side of the labyrinth, this lobular structure presents a roughly hexagonal pattern, with the central maternal stem artery and radially oriented arteriolar branches giving the lobule the shape of a star. These arterioles frequently form bridges to neighboring lobular systems; however, the majority continue into the feto-maternally oriented three-dimensional network of maternal capillary sinusoids, which converge on the outlets of the maternal stem veins on the maternal side of the labyrinth. Maternal main crypts are delimited by the rays of the star-shaped lobules containing chorionic primary villi. The latter penetrate into maternal crypts from the fetal side, and are characterized by their axial arterial and venous stem vessels. Fetal secondary villi are arranged at different levels from these stem vessels. The secondary villi are characterized by arterioles and venules branching in pairs from the stem vessels and supply the tributary capillary complexes of terminal villi. The lobular structure of the placental labyrinth provides a three-dimensional framework of vessels where maternal capillary sinusoids and fetal capillaries meet in a one-way cross-current arrangement. The blood flow conditions and the peculiarities of the mink placenta interhemal membrane are compared to those of other carnivores and discussed with respect to the efficiency of the endotheliochorial placenta.

Calretinin is transiently expressed in tendon fibroblasts of the paravertebral region of the chick embryo

Although calretinin is an intracellular calcium acceptor protein essentially located in neurons, we have previously shown that calretinin was also expressed in the mesenchymal cells forming the intervertebral disc. Here, we describe, using immunohistochemistry, the transient expression of calretinin in fibroblasts responsible for the tendon formation in the paravertebral region. We have looked at chick embryos from embryonic day 4 to day 18. At embryonic day 6, calretinin immunoreactivity was detected in chick embryo cells located laterally to the spinal cord between two groups of developing muscular cells. At embryonic day 8, calretinin immunoreactivity intensity was the highest in cells showing a fibroblast morphology. After embryonic day 8, when fibroblast proliferation decreased and differentiation increased, calretinin immunoreactivity progressively disappeared. Interestingly, calretinin could not be detected in fibroblasts of the anterior and posterior limbs at any investigated age. Because calretinin expression appeared selectively and transiently in the fibroblasts of the paravertebral region, we may conclude that the phenotype of those fibroblasts is different from the limbs fibroblasts.

Localisation of glycans in the placenta: a comparative study of epitheliochorial, endotheliochorial, and haemomonochorial placentation

Specimens of mid-term (horse), near-term (pig, cow, sheep, mink) and term (human) placentae and associated tissues have been examined with a panel of 15 biotinylated lectins combined with an avidin-peroxidase revealing system. The aim of this study has been to analyse the expression of glycans at the materno-fetal interface in order to establish whether the morphological diversity exhibited by these six species is reflected by accompanying biochemical diversity, or whether similar types of glycan are expressed in tissues performing similar functions. Lectin staining intensity was scored in the following elements of the interhaemal placental barrier: maternal capillaries, maternal uterine epithelium, the materno-fetal interdigitating microvillous membrane (brush border in the human), trophoblast, and fetal capillaries. A high degree of biochemical diversity was found in the glycan expression of the various placental components within and among placental types. Each layer showed widely differing patterns of lectin binding between species, with only a few findings in common: 1) the relative lack of simple fucosyl termini, 2) the presence of non-bisected bi/tri-antennary N-glycan in most layers, 3) an abundance of terminal N-acetyl galactosamine, and 4) the restriction of high mannose glycans to intracellular granules. This diversity may be a mechanism to avoid hybridisation, although glycan patterns may change between conception and placental development, or it may have evolved as a consequence of morphological changes. It is possible that it may also be part of the cause, rather than the result, of the structural diversity that is so characteristic of mammalian placentation.