X-Ray Studies on Phospholipid Bilayers, in. Structure and Morphology of L-α-Dilaurylphosphatidylethanolamine (DLPE)

Phospholipid, Bilayer, X-Ray Diffraction, Morphology, Dilaurylphosphatidylethanolam ine, Membrane Powder samples and oriented films of the synthetic phospholipid L-α-dilaurylphosphatidyl-ethanolamine (DLPE) were studied by X-ray diffraction over a wide range of hydration. Only small differences were found between the unit cell dimensions of DLPE powder and oriented-film specimens. These dimensions did not vary appreciably with hydration. In the multilayer DLPE structure, the molecules pack with polar groups parallel to the bilayer plane and hydro­ carbon chains perpendicular to it. Examination of oriented films by scanning electron microscopy gave information on the surface morphology. Complementary data on the lamellar packing of the molecules and the average thickness of the bilayers was provided by thin-section and shadow-cast preparations studied by transmission electron microscopy.

[Postoperative nausea and vomiting and opioid-induced nausea and vomiting: guidelines for prevention and treatment]

Postoperative nausea and vomiting (PONV) causes patient discomfort, lowers patient satisfaction, and increases care requirements. Opioid-induced nausea and vomiting (OINV) may also occur if opioids are used to treat postoperative pain. These guidelines aim to provide recommendations for the prevention and treatment of both problems. A working group was established in accordance with the charter of the Sociedad Española de Anestesiología y Reanimación. The group undertook the critical appraisal of articles relevant to the management of PONV and OINV in adults and children early and late in the perioperative period. Discussions led to recommendations, summarized as follows: 1) Risk for PONV should be assessed in all patients undergoing surgery; 2 easy-to-use scales are useful for risk assessment: the Apfel scale for adults and the Eberhart scale for children. 2) Measures to reduce baseline risk should be used for adults at moderate or high risk and all children. 3) Pharmacologic prophylaxis with 1 drug is useful for patients at low risk (Apfel or Eberhart 1) who are to receive general anesthesia; patients with higher levels of risk should receive prophylaxis with 2 or more drugs and baseline risk should be reduced (multimodal approach). 4) Dexamethasone, droperidol, and ondansetron (or other setrons) have similar levels of efficacy; drug choice should be made based on individual patient factors. 5) The drug prescribed for treating PONV should preferably be different from the one used for prophylaxis; ondansetron is the most effective drug for treating PONV. 6) Risk for PONV should be assessed before discharge after outpatient surgery or on the ward for hospitalized patients; there is no evidence that late preventive strategies are effective. 7) The drug of choice for preventing OINV is droperidol.

[Reticulocyte response after immediate withdrawal of recombinant human erythropoietin in chronic hemodialysis patients]

The sudden interruption of recombinant human erythropoietin (rHuEPO) in end-stage renal disease (ESRD) patients leads to rapid anemization. The mechanisms of this phenomenon are, however, insufficiently understood. The present study examined the response to immediate rHuEPO withdrawal in dialysis patients.

METHODS

10 chronic hemodialysis (HD) patients regularly receiving rHuEPO were studied. rHuEPO was stopped and reinitiated after 7 days. Reticulocyte profile, haemoglobin and haematocrit were measured at 0, 7 and 15 days. As a complementary study, and with the purpose of analyzying whether uremia was a relevant factor, 10 non-uremic male Wistar rats were treated with rHuEPO. After two weeks, rHuEPO was withdrawn in 5 animals, and continued for 7 additional days in the remainder. The same variables than in the human study were determined.

RESULTS

Changes in reticulocyte subtypes from baseline to day 7 were: total 18.2 +/- 0.9 vs 14.3 +/- 1.8% (p < 0.06); high-fluorescence (HFR): 2.6 +/- 0.4 vs 0.75 +/- 0.2 (p < 0.001); medium-fluorescence (MFR): 13.0 +/- 1.1 vs 6.6 +/- 0.9% (p < 0.02); and low-fluorescence (LFR): 84.2 +/- 1.4 vs 92.7 +/- 1% (p NS). The baseline pattern was recovered upon 7 days of rHuEPO reinitiation (p NS). Mean hemoglobin and hematocrit decreased by day 14 (p < 0.02) in spite of rHuEPO reinitiation at day 7. In non-uremic rats, changes were similar to that in the ESRD patients.

CONCLUSION

rHuEPO induces changes in the reticulocyte pattern, consisting in a reduction of immature reticulocytes. These changes appear to be independent of the presence of uremia. Accordingly, complete rHuEPO withdrawal in HD patients will cause a rapidly-developing anaemia due to an alteration in the reticulocyte maturation series; therefore, sudden rHuEPO interruption should be avoided whenever is possible. As a collateral application, the specific changes described herein have potential use for detecting illegal administration of rHuEPO.

[Comparative study of intravenous anesthesia with propofol in continuous perfusion and neuroleptanalgesia in traumatology surgery]

OBJECTIVE. To study propofol as the single agent for both anesthetic induction and maintenance with respect to quality of anesthesia, hemodynamic effects, quality of recovery and analgesic requirements in comparison with neuroleptoanesthesia as the technique of reference. PATIENTS AND METHODS. We selected 2 homogeneous groups of 15 ASA I-III patients undergoing traumatological surgery. Patients were premedicated with bromazepam 3 mg p.o. and droperidol 0.03 mg/kg prior to induction. Induction was achieved with propofol 1.5-2.5 mg/kg in group I (GI) and with sodium thiopental 4-5 mg/kg in group II (GII). Maintenance was by continuous infusion of propofol 6-12 mg/kg in GI and with droperidol 0.15 microgram/kg/h and 50% N2O/O2 in GII. Both groups received fentanyl 4 micrograms/kg/h. Neither analgesia nor curarization were antagonized pharmacologically. Variables recorded were time and quality of anesthetic induction, mean duration of anesthesia, anesthetic education time, time until orientation and time of residual analgesia. Hemodynamic parameters were recorded for both groups at baseline, after induction, at intubation, at 2 and 5 min after intubation, at the start of surgical incision, 30 min after start of incision, and at the end of surgery. Results for the two groups were compared, as were results at the various moments of measurement within groups.

[Anesthesia and perioperative complications of correcting transposition of the great arteries using the Jatene technique]

We present a retrospective morbi-mortality study in 12 patients undergoing Jatene's arterial repair for transposition of the great vessels between 1988 and 1992. Half of the patients were boys ranging in age from 4 days to 35 months. In 34% heart failure was grade III, while in 65.6% it was grade IV (NYHA). Anesthetic induction was with ketamine in 11 patients and with halothane in 1. Maintenance was with pancuronium and fentanyl supplemented with N2O in 2 and with isoflurane in 1. The overall intra- and perioperative death rate was 16.6%. Nine cases have undergone surgical repair since 1988 with no mortality. We conclude that Jatene's technique is the best alternative for repair of transposition of the great vessels when there is no hypoplasia of the right cavity.

X-ray studies on phospholipid bilayers. XIV. Interactions with the antiarrhythmic asocainol

Asocainol (ASOC) belongs to class I of the antiarrhythmic drugs, i.e., those that exert their action at the level of the sodium channels of the myocardial cell membrane. It has been suggested that their molecular mechanism of action might be through nonspecific interactions with phospholipids that surround the channel proteins. In order to test this hypothesis, ASOC was made to interact with two multibilayer systems, one built-up of dimyristoylphosphatidylcholine (DMPC) and the other of dimyristoylphosphatidylethanolamine (DMPE). These are the type of lipids that are respectively found in the outer and inner monolayers of human erythrocytes. The experiments were carried out in a hydrophobic as well as in a hydrophilic medium below the phospholipid main transition temperatures. The perturbing effect of ASOC upon the bilayer structures was determined by X-ray diffraction. It was found that ASOC was able to fluidize DMPC in both media but not to DMPE.

X-ray studies on phospholipid bilayers. XII. Interactions of pentachlorophenol with myelin

Pentachlorophenol (PCP) is a widely used pesticide, particularly for the preservation of wood. Given its high toxicity and resistance to degradation it has become a dangerous environmental pollulant. Due to its high lipophilicity, PCP is able to partition into the lipid bilayer of cell membranes disrupting several vital functions. The present research was concerned with the effects that the chronic administration of PCP could produce in vivo to the sciatic nerve of rats. X-ray diffraction patterns obtained from freshly dissected and dried sciatic nerves of PCP treated rats did not show significant differences in their reflections with respect to those present in the patterns from untreated animals. However, morphological studies performed by optical and electron microscopy showed degenerative changes in about 10% of the A and B type of nerve fibers.

X-ray studies on phospholipid bilayers. X. Interactions with chlortetracycline hydrochloride

This study deals with the structural perturbations that the antibiotic chlortetracycline hydrochloride (CTC) can produce on phospholipid bilayers. Two multibilayer systems, one built-up of dimyristoylphosphatidylethanolamine (DMPE) and the other of dimyristoylphosphatidylcholine (DMPC) were allowed to interact with different concentrations of CTC in the absence and presence of water. The study was carried out by X-ray diffraction methods and all experiments were done below the phospholipid main transition temperatures. The results showed that CTC produced significant perturbations on DMPC even in the absence of water, whereas they were much milder in DMPE.

X-ray studies on phospholipid bilayers. VIII. Interactions with chlorpromazine.HCl

Chlorpromazine is a widely used phenothiazine tranquilizer known to alter the shape of normal erythrocytes and their osmotic fragility. In order to understand the nature of the interactions chlorpromazine.HCl (CPZ.HCl) was made to interact with phospholipid bilayers formed by dimyristoylphosphatidylethanolamine (DMPE) and dimyristoylphosphatidylcholine (DMPC). This study was carried out by X-ray diffraction on crystalline powders of various molar mixtures of CPZ.HCl with DMPE and DMPC, with and without water. It was found that CPZ.HCl significatively affects the bilayer structure of DMPC in the presence of water, but not that of DMPE.

X-ray studies on phospholipid bilayers. V. Interactions with DDT

The possible interaction of DDT with the lipids dimyristoyl lecithin (DML), dipalmitoylphosphatidylethanolamine (DPPE) and tripalmitin (TP) was studied. The work was carried out on oriented films and crystalline powders of DDT-lipid mixtures at different molar ratios by X-ray diffraction techniques. The diagrams showed only the patterns of pure DDT and that of the corresponding lipid. It is concluded that new phases were not formed and, therefore, no interactions occurred.