Spontaneous regression of periodontoid pannus mass in psoriatic atlantoaxial subluxation. Case report

STUDY DESIGN

A case report of a 41-year-old man with psoriasis who had cervical myelopathy caused by atlantoaxial subluxation and periodontoid pannus mass.

OBJECTIVE

To describe the possible mechanism underlying the periodontoid pannus formation and the optimal treatment for such cases.

SUMMARY OF BACKGROUND DATA

Atlantoaxial subluxation causing spinal cord compression at the craniocervical junction may develop in patients with rheumatoid or psoriatic arthritis. Periodontoid pannus formation plays an important role in compromising the anteroposterior diameter of the spinal canal and in causing neurologic deficits. Transoral transpharyngeal excision of the pannus is sometimes thought necessary for anterior decompression of the spinal cord. Spontaneous resolution of the periodontoid pannus after posterior atlantoaxial fusion and fixation has been documented in rheumatoid arthritis, but not in psoriatic arthritis.

METHODS

The patient underwent posterior atlantoaxial fusion and Halifax fixation.

RESULTS

The patient experienced clinical improvement. Regression of the periodontoid pannus mass was observed on magnetic resonance imaging.

CONCLUSIONS

Posterior fusion and instrumentation resulted in spontaneous regression of the pannus mass and symptomatic relief. This report provides evidence that atlantoaxial instability may be the sine qua non for the formation of periodontoid pannus, and that amelioration of such instability leads to spontaneous resolution of the pannus mass.

Effects of exposure protocols on induction of kinetochore-plus and -minus micronuclei by arsenite in diploid human fibroblasts

Arsenic, widely distributed in the environment, is a potent human carcinogen. Arsenite genotoxicity has been observed in a variety of cells and animal systems. However, the underlying mechanism is not completely clear. In this study, human fibroblasts (HFW) were treated with 1.25-10 microM arsenite for 24 h (low dose and long exposure) and 5-80 microM for 4 h (high dose and short exposure), and the arsenite accumulation, cytotoxicity, and micronucleus (MN) induction were examined. By these two different protocols, HFW cells showed equivalent levels of arsenite accumulation, but exhibited different kinetics of cell killing and different types of MN generation. Arsenite induced mainly kinetochore-positive MN (K+-MN) in HFW cells by low dose exposure whereas mainly kinetochore-negative MN (K--MN) was induced by high dose exposure. Catalase reduced both K+- and K--MN induced by these two exposure protocols. Except for the case of K+-MN induction by the high dose exposure protocol, N-acetyl-cysteine (NAC) in both low and high dose protocols was also shown to effectively reduce arsenite-induced MN. The present results imply that oxidative stress is involved in arsenite-induced MN in diploid human fibroblasts. However, different protocols for arsenite exposure may result in different cellular damage.

Exposure to disgust-evoking imagery and information processing biases in blood-injection-injury phobia

Biased processing of threat-relevant information is a central construct among contemporary theories of anxiety. However, biases in attentional and memory processes have not been systematically investigated in blood-injection-injury (BII) phobia. Theory has suggested that disgust rather than fear characterizes BII phobia and may mediate processing biases differently. We investigated the effects of a disgust mood induction on attention and memory in BII phobic and nonphobic participants. The Stroop task failed to demonstrate an attentional bias toward medical and disgust words, even under conditions of disgust provocation. However, an implicit memory task showed that BII phobics completed more medical and disgust word stems than nonphobics. These results suggest that BII phobia may be characterized by a similar implicit memory, but not an attentional, bias found in other anxiety disorders. As such, information processing in BII phobia may be qualitatively different from other anxiety disorders. Implications for further research regarding information processing biases in BII phobia are discussed.

Plant alkaloid tetrandrine downregulates protein kinase C-dependent signaling pathway in T cells

Tetrandrine, a purified traditional Chinese medicinal herb that acts as an immunosuppressant and a Ca2+ channel blocker, has been clinically used to treat patients with arthritis, silicosis and hypertension. Since T cells play a critical role as autoreactive and pathogenic population in autoimmune diseases, in this study, we examined the immunosuppressive effect of tetrandrine on human peripheral blood T cells. We showed that tetrandrine inhibited phorbol 12-myristate 13-acetate (PMA) + ionomycin-induced T cell proliferation, interleukin-2 secretion and the expression of the T cell activation antigen, CD71. Further investigation of the molecular mechanism demonstrated that tetrandrine inhibited the expression of the protein kinase C-dependent interleukin-2 receptor alpha chain and CD69 but not the expression of the Ca2+-dependent CD40 ligand and CD69. Interestingly, when tetrandrine and cyclosporin A were added together, significant synergism in the suppression of T cell activation was observed. Moreover, of the several tetrandrine analogues studied, hernandezine was the most potent inhibitor of protein kinase C signaling events. These results also suggest that the protein kinase C-inhibitory capacity of tetrandrine and its analogues may not be associated with their function as Ca2+ channel blockers. Lastly, we showed that, within therapeutic concentrations, tetrandrine and its analogues could induce cellular apoptosis, which is defective in autoimmune diseases. In conclusion, our findings provide novel information about the molecular mechanism of the immunosuppressive effect of tetrandrine and its analogues in human peripheral blood T cells.

Sodium arsenite enhances copper accumulation in human lung adenocarcinoma cells

In this report, we found that arsenite-resistant human lung adenocarcinoma cells, CL3R15, were more susceptible to CuCl2 than the parental CL3 cells. With the aid of atomic absorption spectrophotometry, we observed that CL3R15 cells accumulated more copper than CL3 cells. We further demonstrated that sodium arsenite treatment resulted in a dose-dependent increase of copper accumulation in the parental CL3 cells. In contrast, copper did not alter the levels of intracellular arsenite in CL3 cells treated in combination with sodium arsenite and CuCl2. Pretreatment of CL3 cells with sodium arsenite resulted in a significant increase of copper accumulation and cytotoxicity. These results indicate that intracellular copper accumulation is enhanced by arsenite. However, arsenite-enhanced copper accumulation was not observed in two fibroblastic cells, GM00220 and GM03700, derived from Menkes patients. The Menkes gene encodes a membrane pump responsible for copper exportation. Our results suggest that Menkes protein is a potential target of arsenite.

Population pharmacokinetic modeling in very premature infants receiving midazolam during mechanical ventilation: midazolam neonatal pharmacokinetics

BACKGROUND

Midazolam is used widely as a sedative to facilitate mechanical ventilation. This prospective study investigated the population pharmacokinetics of midazolam in very premature infants.

METHODS

Midazolam (100 microg/kg) was administered as a rapid intravenous bolus dose every 4-6 h to 60 very premature neonates with a mean (range) gestational age of 27 weeks (24-31 weeks), a birth weight of 965 g (523-1,470 g), and an age of 4.5 days (2-15 days). A median (range) of four (one to four) blood samples, 0.2 ml each, were drawn at random times after the first dose or during continuous treatment, and concentrations of midazolam in serum were assayed by high-performance liquid chromatography. A population analysis was conducted using a two-compartment pharmacokinetic model using the NONMEM program.

RESULTS

Average parameter values (interpatient percent coefficient of variation) for infants with birth weights 1,000 g or less were total systemic clearance (Cl(T)) = 0.783 ml/min (83%), intercompartmental clearance (Cl(Q)) = 6.53 ml/min (116%), volume of distribution of the central compartment (V1) = 473 ml (70%), and volume of distribution of the peripheral compartment (V2) = 513 ml (146%). For infants with birth weights more than 1,000 g they were as follows: Cl(T) = 1.24 ml/min (78%), Cl(Q) = 9.82 ml/min (98%), V1 = 823 ml (43%), and V2 = 1,040 ml (193%). The intrapatient variability (percent coefficient of variation) in the data was 4.5% at the mean concentration midazolam in serum of 121 ng/mL.

CONCLUSIONS

Serum concentration-time data were used in modeling the population pharmacokinetics of midazolam in very premature, ventilated neonates. Clearance of midazolam was markedly decreased compared with previous data from term infants and older patients. Infants weighing less than 1,000 g at birth had significantly lower clearance than those weighing more than 1,000 g.

Mxi1 is a repressor of the c-Myc promoter and reverses activation by USF

The basic region/helix-loop-helix/leucine zipper (B-HLH-LZ) oncoprotein c-Myc is abundant in proliferating cells and forms heterodimers with Max protein that bind to E-box sites in DNA and stimulate genes required for proliferation. A second B-HLH-LZ protein, Mxi1, is induced during terminal differentiation, and forms heterodimers with Max that also bind E-boxes but tether the mSin3 transcriptional repressor protein along with histone deacetylase thereby antagonizing Myc-dependent activation. We show that Mxi1 also antagonizes Myc by a second pathway, repression of transcription from the major c-myc promoter, P2. Repression was independent of Mxi1 binding to mSin3 but dependent on the Mxi1 LZ and COOH-terminal sequences, including putative casein kinase II phosphorylation sites. Repression targeted elements of the myc P2 promoter core (-35/+10), where it reversed transactivation by the constitutive transcription factor, USF. We show that Zn2+ induction of a stably transfected, metallothionein promoter-regulated mxi1 gene blocked the ability of serum to induce transcription of the endogenous c-myc gene and cell entry into S phase. Thus, induction of Mxi1 in terminally differentiating cells may block Myc function by repressing the c-myc gene P2 promoter, as well as by antagonizing Myc-dependent transactivation through E-boxes.

Visual avoidance in specific phobia

Cognitive models of anxiety postulate that fear and anxiety serve as programs for avoidance of threat-relevant stimuli. We hypothesized that exposure to phobia-relevant stimuli would lead to visual avoidance in specific phobics. Spider phobic, blood-injection-injury phobic, and nonphobic participants were asked to view spider, injection, and neutral photographs through a three-channel tachistoscope that measured viewing time for each picture. Despite experimenter instructions to study the pictures carefully for a subsequent recognition test, phobic subjects showed decreased viewing times for threat-relevant pictures as compared to neutral pictures. Results are discussed in terms of cognitive models of anxiety disorders and implications for exposure-based therapies.

On a wing and a prayer: the biomechanics of the Rev. Dr. Samuel Haughton (1821-1897)

In 1873, Samuel Haughton published Principles of Animal Mechanics. Based on research begun in 1862, it was a response to Darwin's The Origin of Species by Means of Natural Selection published three years earlier. In this article, the nature of Haughton's biomechanical researches is described by reviewing and re-analysing some of his original work. He showed how muscles could be seen as designed to carry out the maximum amount of work with the least expenditure of energy. Haughton used the results to argue against Darwin's theory of natural selection, the "unproved hypothesis" as Haughton called it. Despite correspondence with Darwin, Haughton received no scientific rebuttal of his arguements. To this day, it would seem, there is a lack of concordance between the biomechanical view of organic life as "optimised" and the evolutionary view of life under continual transformation as organic forms descended "from a supposed common ancestor."

Development of expanded extrusion food products for an Advanced Life Support system

Extrusion processing was proposed to provide texture and to expand the variety of cereal food products in an isolated Advanced Life Support (ALS) system. Rice, wheat, and soy are the baseline crops selected for growing during long-term manned space missions. A Brabender single-screw laboratory extruder (model 2003, L/D 20:1), equipped with round nozzles of various lengths, was used as a prototype of a small-size extruder. Several concepts were tested to extend the variety and improve the quality of the products, to decrease environmental loads, and to promote processing stability. These concepts include: the blending of wheat and soybean flour, the extrusion of a coarser rice flour, separation of wheat bran, and optimization of the extruder nozzle design. An optimal nozzle length has been established for the extrusion of rice flour. Bran separating was necessary to improve the quality of wheat extrudates.

Closed reduction of bilateral locked facets of the cervical spine under general anaesthesia

BACKGROUND

Bilateral facet interlocking of the cervical spine is a relatively uncommon type of cervical spinal injury. It is frequently associated with devastating neurological symptoms and signs. Early reduction of the locked facets is thought to be critical in preventing progressive secondary spinal cord injury. Whereas skull tong traction remains our primary option for closed reduction of bilateral locked facets of the cervical spine, it is not always successful, even with heavy traction weights. Other more aggressive measures may occasionally be required. The authors report their experience in reducing bilateral locked facets of the cervical spine by manual closed reduction.

METHODS

This small series consists of six cases of cervical spinal injury with bilateral locked facets in which manual closed reduction under general anaethesia and muscle relaxation was used. Three of them presented with complete quadriplegia (Frankel class A). One case presented with incomplete but severe neurological deficits (Frankel class B). After unsuccessful closed reduction with skull traction, these patients were treated by manual closed reduction under general anaesthesia and muscle relaxation, followed by anterior discectomy, interbody fusion and stabilization.

RESULTS

All cases made neurological improvement after the procedures. Even in cases with initial severe neurological deficits, the recovery was remarkable. The recovery was dramatic in two cases. Case 1 improved from Frankel class B to E; and Case 5 from Frankel class A to D. No case deteriorated neurologically after the procedures. Pneumonia occurred in Case 3; and stress ulcer accompanied by haemorrhage was noted in Case 4. None of these complications was directly related to the procedures.

CONCLUSION

The potential for improvement of neurological function following early and successful reduction and fixation of the dislocated spine is emphasized. With meticulous techniques, manual closed reduction may be an effective alternative to skull tong traction when the latter fails.

Successful removal of a hemangioblastoma from the medulla oblongata: case report

Hemangioblastomas are histologically benign tumors that occur exclusively within the neuraxis, most commonly in the posterior fossa. They are typically cystic tumors located in the cerebellum. Excision of the vascular mural nodules leads to cure. Brain stem lesions are rarely reported. Surgical extirpation of a solid brain stem hemangioblastoma is relatively risky and requires precise microsurgical techniques. We present a woman with a hemangioblastoma embedded in the medulla oblongata. This 33-year-old woman presented with occipital headaches and sensory ataxia. Complete and detailed preoperative imaging studies were followed by successful microsurgical excision of the lesion. The patient recovered completely within 2 weeks after the operation except for mild paresthesia of the legs. Preoperative magnetic resonance imaging and cerebral angiography provided important information regarding the nature, location, and blood supply of this lesion, which facilitated its total removal. The importance of intraoperative identification and control of the feeding artery of the tumor is emphasized.

Measuring the shape and size of microcracks in bone

Microcracks in bone are normally measured from two-dimensional, transverse sections but this provides incomplete information about their three-dimensional shape and size. The methods of stereology can usefully be applied in such a case. This problem has been addressed using a theoretical model and a numerical simulation. Results show that the data are consistent with a crack shape which is elliptical, with axis ratio approximately 4.5:1 and with size variation (expressed as the ratio of standard deviation to mean length) of at least 0.1. Measured lengths will, on average, be smaller and have more scatter than true lengths. Errors caused by omitting small cracks are relatively unimportant. Knowledge of the true crack dimensions, and their variability, is important for the analysis of damage, stress fracture, remodelling and adaptation.

New system for long-term monitoring of sperm motility: EDTA effect on semen

Many drugs act as sperm stimulants and are of clinical value for male infertility. Current research deals with the physiological mechanisms of sperm motility/sperm stimulation and how long the effect lasts. For such a study, long-term monitoring of sperm motility becomes essential for traditional semen evaluation. A new system was designed to deal with the microscopic images of semen. Its performance was evaluated by studying the effect of EDTA on sperm motility. EDTA increased sperm curvilinear velocity (Vcl) and straight-line velocity (Vsl) by 31 and 20%. EDTA also prolonged the duration of motility by 68 and 61%, respectively. However, EDTA had less effect on the linearity of forward progression (Lin). The proposed system can analyze semen and does well at monitoring sperm motility for short term and long term. It may be valuable to test the possible role of sperm stimulation for male infertility and assisted reproduction.

Lidocaine concentrations in plasma and cerebrospinal fluid after systemic bolus administration in humans

Preclinical studies suggest that systemic lidocaine acts at the level of the spinal dorsal horn to inhibit hyperalgesia resulting from nerve injury, yet no clinical data are available to support this view. Therefore, we sought to characterize the time course of lidocaine in the plasma and cerebrospinal fluid (CSF) after an IV bolus injection of lidocaine 2 mg/kg in patients scheduled for surgery involving spinal anesthesia. Sixty-five patients were randomly allocated to one of five study groups (n = 13 per group) receiving IV lidocaine before CSF/ plasma sampling at 5, 10, 15, 30, or 60 min. Gas chromatographic analysis of these samples revealed a fast but transient peak (5-15 min) in lidocaine plasma levels (1.7+/-0.16 microg/mL), which declined rapidly thereafter. Only small concentrations of IV lidocaine were found in the CSF (6%- 8% of plasma concentration), but this fraction remained stable from 15 min until termination of the experiment. No statistical correlation was observed between plasma and CSF lidocaine levels. These data suggest that because of the prolonged availability of lidocaine at the spinal dorsal horn level, systemic administration of lidocaine suppresses central sensitization within the spinal cord after nerve injury in humans.

IMPLICATIONS

Cerebrospinal fluid concentrations of lidocaine after its systemic bolus delivery in humans indicate that the spinal cord may be the major site of antinociceptive action by this route of drug administration.

Fluorescence-aided detection of microdamage in compact bone

En bloc staining with basic fuchsin is an established method for demonstrating microdamage in bone. Using transmitted light microscopy, variations in light intensity, depth of focus and magnification are necessary to distinguish fully-stained microcracks generated in vivo, from partially-stained or unstained artefactual cracks due to cutting and machining. This process is both difficult and time-consuming. In this study, 2 methods were used to examine fuchsin-stained microcracks in human rib sections, transmitted light and epifluorescence microscopy. No differences were found in crack number, density or length between the 2 methods indicating comparable accuracy. Using green epifluorescence, only microcracks containing fuchsin fluoresced orange against the darkfield background, enabling unstained, artefactual cracks to be screened out. Under UV epifluorescence, microcracks stained through the full 100 microm depth of the section fluoresced purple. Partially-stained artefactual cracks failed to fluoresce and were screened out. Epifluorescence is a simple, rapid and accurate screening method for differentiating fully-stained from artefactual microcracks in bone.

Types of purinoceptors and phospholipase A2 involved in the activation of the platelet-activating factor-dependent transacetylase activity and arachidonate release by ATP in endothelial cells

Acyl analogs of PAF are the major products synthesized during agonist stimulation of endothelial cells. We have previously shown that PAF: 1-acyl-2-lyso-sn-glycero-3-phosphocholine transacetylase in calf pulmonary artery endothelial cells is activated by ATP through protein phosphorylation, and the increase in transacetylase activity by ATP contributes to the biosynthesis of acyl analogs of PAF (J. Biol. Chem. 272, 17431-17437, 1997). To understand the mechanisms(s) by which ATP stimulates acyl analogs of PAF production, we have identified the subtypes of the purinergic receptor that are linked to the activation of two enzymes involved in the generation of acyl analogs of PAF, namely, transacetylase and phospholipase A2. Experiments with transient transfection of the cells with antisense and sense thio-oligonucleotide to cytosolic phospholipase A2 (cPLA2) were also performed to evaluate whether downstream activation of cPLA2 is involved in ATP-receptor mediated induction of arachidonate release and synthesis of radylacetyl-GPC. We found that the P2u/P2Y2 receptor, which recognizes a pyrimidine nucleotide, UTP, as well as purine nucleotides, shows a potency profile of UTP > ATP = ATP gamma S > 2-methylthio-ATP in mediating the activation of PAF: lysophospholipid transacetylase. On the other hand, ADP beta S and 2-methylthio-ATP have similar potencies as ATP but have lower potencies than UTP and ATP gamma S in stimulating the release of arachidonate. These results suggest that both P2u/P2Y2 and P2y/P2Y1 receptor subtypes promote arachidonate release. In addition, transient transfection of endothelial cells with cPLA2 antisense but not the sense thio-oligonucleotide inhibited the stimulation of arachidonate release and [3H]acetate incorporation into radyl[3H]acetyl-GPC. Thus, our data suggest that a receptor-mediated process is involved in the activation of transacetylase for the induced synthesis of acyl analogs of PAF in endothelial cells. Furthermore, it is likely that cPLA2 supplies the lysophospholipids as substrates for the transacetylation reaction.

Induction of pulmonary fibrosis in organ-cultured rat lung by cadmium chloride and transforming growth factor-beta1

Cadmium chloride (CdCl2) exposure has been reported to induce pulmonary fibrosis in rats. Accumulating evidence has shown that cytokines play a pivotal role in the excessive production of connective tissue components in pulmonary fibrosis. In this report, rat lung slice cultures were used to study the synergistic involvement of transforming growth factor-beta1 (TGF-beta1) in CdCl2-induced alveolar fibrosis. Rat lung slices were maintained at the interphase of air and medium on a polyester mesh stretched on a plastic scaffold. Treatment of lung slices with 2.5, 5 or 10 microM CdCl2 for 7 days resulted in 85, 40 and 6% respectively for relative survival. Under these culture conditions, CdCl2 alone did not induce alveolar fibrosis in rat lung slices. However, in the presence of 0.5 ng/ml TGF-beta1, CdCl2 at a dose ranging from 1 to 5 microM increased the thickness of alveolar septa. Furthermore, the thickness of alveolar septa in lung slices treated with CdCl2 was dose-dependently increased by the presence of TGF-beta1. The thickened alveolar septa were apparently due to the deposition of excessive extracellular matrix, as revealed by trichrome stain and ultrastructural examination. Our results also show that fibrogenic activity induced by the combined treatment with CdCl2 and TGF-beta1 can be reduced by co-treatment with 200 microg/ml lambda-carrageenan, a TGF-beta1 inhibitor. Therefore, the present results indicate that TGF-beta1 can synergistically stimulate the fibrogenic activity in lung tissue subsequent to CdCl2 injury.

Induction of sister chromatid exchanges and micronuclei by titanium dioxide in Chinese hamster ovary-K1 cells

Titanium dioxide (TiO2) has color properties of extreme whiteness and brightness, is relatively inexpensive, and is extensively used as a white pigment in a variety of materials. TiO2, an effective blocker of ultraviolet light, is frequently added to sunscreens and cosmetic creams. However, the genotoxicity of TiO2 remains to be controversial. In this report, we have demonstrated that TiO2 can be transported into Chinese hamster ovary-K1 (CHO-K1) cells. The effects of TiO2 on induction of sister chromatid exchanges (SCE) and micronuclei (MN) were then studied in these cells. The SCE frequency in CHO-K1 cells treated with TiO2 at a nonlethal dose range (0 to 5 microM) for 24 h was significantly and dose-dependently increased. By the conventional MN assay, TiO2 at the dose ranged from 0 to 20 microM slightly increased the MN frequency in CHO-K1 cells. However, in the cytokinesis-block MN assay, the number of MN per 1000 binucleated cells was significantly and dose-dependently enhanced in CHO-K1 cells treated TiO2 at the same dose range for 24 h. These results suggest that TiO2 is a potential genotoxic agent.

Arsenite inhibits mitotic division and perturbs spindle dynamics in HeLa S3 cells

Arsenical compounds, known to be human carcinogens, were shown to disturb cell cycle progression and induce cytogenetic alterations in a variety of cell systems. We report here that a 24 h treatment of arsenite induced mitotic accumulation in human cell lines. HeLa S3 and KB cells were most susceptible: 35% of the total cell population was arrested at the mitotic stage after treatment with 5 microM sodium arsenite in HeLa S3 cells and after 10 microM in KB cells. Under a microscope, we observed abnormal mitotic figures in arsenite-arrested mitotic cells, including deranged chromosome congression, elongated polar distance of mitotic spindle, and enhanced microtubule immunofluorescence. The spindle microtubules of arsenite-arrested mitotic cells were more resistant to nocodazole-induced dissolution than those of control mitotic cells. According to turbidity assay, arsenite at concentrations below 100 microM significantly enhanced polymerization of tubulins. Since spindle dynamics play a crucial role in mitotic progression, our results suggest that arsenite-induced mitotic arrest may be due to arsenite's effects on attenuation of spindle dynamics.

Effect of patient position and hypotensive anesthesia on inferior vena caval pressure

STUDY DESIGN

This is a prospective study to measure the inferior vena caval pressure of 20 patients in different positions and different states of blood pressure.

OBJECTIVES

Because the inferior vena caval pressure could affect the vertebral venous pressure, which in turn may influence blood loss during lumbar spinal surgery, this study was designed to provide the quantitative data necessary to stress the importance of patient positioning and to assess the effect of controlled hypotension on inferior vena caval pressure.

SUMMARY OF BACKGROUND DATA

Positioning patients with a pendulous abdomen and controlled hypotension has been practiced widely during lumbar spinal surgery. It is generally believed that the former will help reduce vertebral venous engorgement and the latter will produce a bloodless surgical wound. However, there have been no complete studies in which quantitative changes of inferior vena caval pressure resulting from different positions was examined. In addition, it would be interesting to know what happens to inferior vena caval pressure during induced hypotension. Could there be an adverse effect on the inferior vena caval pressure during the hypotensive state?

METHODS

An intravenous catheter was introduced into the inferior vena cava in each of 20 patients undergoing spinal surgery. In each patient, the inferior vena caval pressure was measured when the patient was supine, prone on a conventional pad, and prone on a Relton-Hall frame. It was followed by isoflurane-induced hypotension with reduction of mean arterial pressure by 20 mm Hg.

RESULTS

In this series, the inferior vena caval pressure ranged from 8.2 to 23.4 mm Hg (with a mean of 15.3 mm Hg) when patients were positioned prone on a conventional pad. However, when they were subsequently positioned prone on a Relton-Hall frame, the inferior vena caval pressure decreased dramatically to a range of 4.6 to 13.6 mm Hg (with a mean of 8.2 mm Hg). In each patient the measured inferior vena caval pressure when positioned prone on a conventional pad was 1.5 times greater than that measured with the patient positioned on a Relton-Hall frame. There was a statistically significant difference between these two positions (F = 75.996; P < 0.05). The patients' mean arterial pressure ranged from 92 to 105 mm Hg before induced hypotension. During this time, the inferior vena caval pressure ranged from 4.1 to 13.1 mm Hg (mean, 8.2 mm Hg). During the hypotensive state, the patients' inferior vena caval pressure was found to range from 4.2 to 13.6 mm Hg (mean, 8.1 mm Hg). In each patient the hypotensive interior vena caval pressure may be slightly higher or lower than the baseline pressure. However, the variation never exceeded 1.7 mm Hg. Statistically, there was no significant difference between these two periods (t = 0.956; P > 0.05).

CONCLUSIONS

A device allowing the patient's abdominaL viscera to hang freely while the patient is in a prone position significantly reduces their inferior vena caval pressure. The patients also has a constant inferior vena caval pressure during isoflurane-induced hypotension.

Cytochrome b5 augments the 17,20-lyase activity of human P450c17 without direct electron transfer

In the biosynthesis of steroid hormones, P450c17 is the single enzyme that catalyzes both the 17alpha-hydroxylation of 21-carbon steroids and the 17,20-lyase activity that cleaves the C17-C20 bond to produce C19 sex steroids. Cytochrome b5 augments the 17,20-lyase activity of cytochrome P450c17 in vitro, but this has not been demonstrated in membranes, and the mechanism of this action is unknown. We expressed human P450c17, human P450-oxidoreductase (OR), and/or human cytochrome b5 in Saccharomyces cerevisiae and analyzed the 17alpha-hydroxylase and 17,20-lyase activities of the resulting yeast microsomes. Yeast expressing only P450c17 have 17alpha-hydroxylase and trace 17,20-lyase activities toward both Delta4 and Delta5 steroids. Coexpression of human OR with P450c17 increases the Vmax of both the 17alpha-hydroxylase and 17,20-lyase reactions 5-fold; coexpression of human b5 with P450c17 also increases the Vmax of the 17,20-lyase reactions but not of the 17alpha-hydroxylase reactions. Simultaneous expression of human b5 with P450c17 and OR, or addition of purified human b5 to microsomes from yeast coexpressing human P450c17 and OR, further increases the Vmax of the 17,20-lyase reaction without altering 17alpha-hydroxylase activity. Genetically engineered yeast and mixing experiments demonstrate that OR is both necessary and sufficient for microsomal 17,20-lyase activity. Addition of purified human holo-b5, apo-b5, or cytochrome c to microsomes containing both human P450c17 and OR demonstrate that the stimulatory action of b5 does not require electron transfer from b5 to P450c17. These data suggest that human b5 acts principally as an allosteric effector that interacts primarily with the P450c17.OR complex to stimulate 17, 20-lyase activity.

The regulation of human P450c17 activity: relationship to premature adrenarche, insulin resistance and the polycystic ovary syndrome

The polycystic ovary syndrome (PCOS) is characterized by hyperandrogenism and insulin resistance, but the connection between these two features has been unclear. Androgen synthesis is regulated in part by the ratio of the 17alpha-hydroxylase and 17,20 lyase activities of P450c17. Three separate lines of evidence show that the ratio of lyase to hydroxylase activity is regulated by electron flow from P450 oxidoreductase. Lyase activity and androgen synthesis are particularly dependent on the serine phosphorylation of P450c17. Serine phosphorylation of the insulin receptor beta chain causes insulin resistance, and some PCOS women have hyperphosphorylated receptors. We hypothesize that an overactive serine/threonine kinase hyperphosphorylates both the insulin receptor and P450c17 in PCOS, accounting for the characteristic insulin resistance and hyperandrogenism of this disease.