Analysis of Cholesterol in All Lipoprotein Classes by Single Vertical Ultracentrifugation of Fingerstick Blood and Controlled-Dispersion Flow Analysis

This new, highly sensitive analytical system, based on controlled dispersion of the flowing sample, gives a rapid, continuous, and direct analysis for cholesterol in all lipoprotein classes, separated by single vertical-spin density-gradient ultracentrifugation. In this Vertical Auto Profile-II fingerstick system, designated VAP-IIfs, a narrow-bore Teflon coil serves as the reactor with no segmentation of the analytical stream by air bubbles, in contrast to the Technicon AutoAnalyzer used in the VAP-I method. Concentrations of high-, low-, intermediate-, and very-low-density lipoprotein cholesterol and lipoprotein(a) cholesterol are determined by decomposing the spectrophotometric absorbance curve for the continuous analysis of the centrifuged sample, with use of software developed in this laboratory. Total cholesterol is determined from the total area under the absorbance curve. For assaying total cholesterol, the CV between aliquots within a rotor ranged from 1.35% to 3.15%; the CV between rotors was 2.45%. Because only 18 microL of sample is required, VAP-IIfs can be readily adapted to analysis for lipoprotein cholesterol profiles in capillary blood samples. Total cholesterol values by VAP-IIfs for fingerstick and venous samples from 23 subjects agreed well: slope = 1.01 (SD 0.03), intercept = -21 (SD 51) mg/L, Sy/x = 50 mg/L, and r = 0.992. Results by VAP-IIfs also correlated highly with results for duplicate samples analyzed at the Northwest Lipid Research Laboratories.

The effects of global warming on allergic diseases

Global warming is a public health emergency. Substantial scientific evidence indicates an unequivocal rising trend in global surface temperature that has caused higher atmospheric levels of moisture retention leading to more frequent extreme weather conditions, shrinking ice volume, and gradually rising sea levels. The concomitant rise in the prevalence of allergic diseases is closely related to these environmental changes because warm and moist environments favour the proliferation of common allergens such as pollens, dust mites, molds, and fungi. Global warming also stresses ecosystems, further accelerating critical biodiversity loss. Excessive carbon dioxide, together with the warming of seawater, promotes ocean acidification and oxygen depletion. This results in a progressive decline of phytoplankton and fish growth that in turn promotes the formation of larger oceanic dead zones, disrupting the food chain and biodiversity. Poor environmental biodiversity and a reduction in the microbiome spectrum are risk factors for allergic diseases in human populations. While climate change and the existence of an allergy epidemic are closely linked according to robust international research, efforts to mitigate these have encountered strong resistance because of vested economic and political concerns in different countries. International collaboration to establish legally binding regulations should be mandatory for forest protection and energy saving. Lifestyle and behavioural changes should also be advocated at the individual level by focusing on low carbon living; avoiding food wastage; and implementing the 4Rs: reduce, reuse, recycle, and replace principles. These lifestyle measures are entirely consistent with the current recommendations for allergy prevention. Efforts to mitigate climate change, preserve biodiversity, and prevent chronic diseases are interdependent disciplines.

Effects of testosterone administration on cognitive function in hysterectomized women with low testosterone levels: a dose-response randomized trial

PURPOSE

To determine the dose-dependent effects of testosterone administration on cognition in women with low testosterone levels.

METHODS

71 hysterectomized women with or without oophorectomy with total testosterone <31 ng/dl and/or free testosterone <3.5 pg/ml received a standardized transdermal estradiol regimen during the 12-week run-in period and were then randomized to receive weekly intramuscular injections of placebo, 3, 6.25, 12.5, or 25 mg testosterone enanthate for 24 weeks. Total testosterone was measured in serum by LC-MS/MS, and free testosterone levels were measured by equilibrium dialysis. Cognitive function was evaluated using a comprehensive battery of standardized neuropsychological tests at baseline and 24 weeks.

RESULTS

46 women who had baseline and end-of-treatment cognitive function data constituted the analytic sample. The five groups were similar at baseline. Mean on-treatment nadir total testosterone concentrations were 15, 89, 98, 134, and 234 ng/dl in the placebo, 3, 6.25, 12.5, and 25 mg groups, respectively. No significant changes in spatial ability, verbal fluency, verbal memory, or executive function were observed in any treatment arm compared to placebo even after adjustment for baseline cognitive function, age, and education. Multiple regression analysis did not show any significant relation between changes in testosterone concentrations and change in cognitive function scores.

CONCLUSION

Short-term testosterone administration over a wide range of doses for 24 weeks in women with low testosterone levels was neither associated with improvements nor worsening of cognitive function.

Dural sinus thrombosis owing to polycythaemia vera in a 12-year-old girl

Because of the rarity of dural sinus thrombosis in children with polycythaemia vera (PV), the options for diagnosis and treatment remain elusive. A 12-year-old girl was admitted with dural sinus thrombosis associated with PV, diagnosed by magnetic resonance venography. She was managed with interventional endovascular thrombolectomy and venoplasty, phlebotomy, hydroxyurea, low molecular weight heparin, and aspirin followed by warfarin. She made a good recovery without residual neurological deficit. This case highlights the importance of diagnosis and appropriate intervention with multi-modality treatments in patients with PV and thrombosis.

Tension-free transobturator tape procedure for stress urinary incontinence

PURPOSE OF REVIEW

Recent data on the tension-free transobturator tape procedure for the treatment of female stress urinary incontinence are reviewed.

RECENT FINDINGS

Although long-term data are not available, the effectiveness and safety of the tension-free transobturator tape procedure as reported during the past 5 years are very promising and this procedure is becoming a popular surgical treatment for female stress urinary incontinence. The continence rates obtained have been similar to those obtained using the retropubic tension-free vaginal tape on short-term follow-up. Clinical data as well as studies on cadaveric dissections suggest that complication rates can be decreased significantly with the transobturator approach. In the original tension-free transobturator tape procedure, the tape is inserted through the obturator foramen from the outside-to-inside direction (skin incision to vaginal incision). The inside-to-outside approach with passage of the tape from the vaginal incision to the obturator foramen has also been described.

SUMMARY

The tension-free transobturator tape procedure provides a useful alternative to the retropubic tension-free vaginal tape approach while maintaining the principles of tension-free midurethral support. By avoiding the intrapelvic and retropubic passage, complications can be decreased. The effectiveness of this approach is similar to that of tension-free vaginal tape on short-term follow-up.

Cutaneous tuberculosis in Hong Kong: an update

OBJECTIVE

To provide an update on cutaneous tuberculosis in Hong Kong.

DESIGN

Retrospective study.

SETTING

Social Hygiene Service (Dermatology Division), the largest dermatological referral centre in Hong Kong.

PATIENTS

Patients presented with cutaneous tuberculosis between 1993 and 2002 inclusive. Case notes, histology reports, and microbiological reports were reviewed with particular reference to the epidemiology, duration of illness, history of contact with tuberculosis, culture results, and response to treatment.

RESULTS

There were 147 patients with cutaneous tuberculosis; among these a few had true cutaneous tuberculosis (n = 16) and the remainder were tuberculids (n = 131). In all they accounted for 0.04% of new dermatology cases diagnosed. Cases of cutaneous tuberculosis were distributed as follows: lupus vulgaris (n = 6, 4%), tuberculosis verrucosa cutis (n = 6, 4%), tuberculosis of the skin unclassified (n = 2, 1%), and orificial tuberculosis (n = 2, 1%). Culture and polymerase chain reaction was positive in less than half of the latter cases. All responded well to anti-tuberculosis therapy. Erythema induratum was the most common form (n = 127, 86%), but papulonecrotic tuberculids (n = 4, 3%) were uncommon. Erythema induratum affected the lower limb in all patients, with a female predominance, and responded to isoniazid monotherapy, multidrug anti-tuberculosis therapy, or doxycycline.

CONCLUSION

Lupus vulgaris and tuberculosis verrucosa cutis remain the commonest forms of true cutaneous tuberculosis, and erythema induratum is the most common tuberculid. Culture and polymerase chain reaction are positive in a small proportion of patients.

Atypical mycobacterial cutaneous infections in Hong Kong: 10-year retrospective study

OBJECTIVE

To review the epidemiology of atypical mycobacterial cutaneous infection in Hong Kong.

DESIGN

Retrospective study.

SETTING

Social Hygiene Service (Dermatology Division), the largest dermatological referral centre in Hong Kong.

PATIENTS

Patients with a diagnosis of atypical mycobacterial cutaneous infection based on clinical features, histopathology, with or without a positive culture during the period 1993 to 2002.

MAIN OUTCOME MEASURES

Epidemiological data, clinical features, histology, microbiological investigation, and treatment response.

RESULTS

Of 345,394 dermatological cases presented over the 10-year period, 33 (0.0096%) cases (19 male, 14 female) of atypical mycobacterial cutaneous infection were diagnosed. The most common type of infection was caused by Mycobacterium marinum (n=17, 51.5%), followed by Mycobacterium avium-intracellulare (n=3, 9.1%) and Mycobacterium chelonae (n=2, 6.1%). The upper limb, especially the hands and fingers, was the most common (69.7%) site of involvement. Tissue culture was positive in 18 (54.5%) cases. All biopsies showed granulomatous histology. Thirty-two patients received treatment and 31 responded. Twenty-six were treated with oral tetracycline group of antibiotics (minocycline, doxycycline, tetracycline). The duration of treatment ranged from 8 to 54 weeks (mean, 24 weeks). Mild transient adverse effects to treatment were reported in six cases.

CONCLUSION

Atypical mycobacterial infection is rare in Hong Kong. Because of the low sensitivity of traditional culture techniques, atypical mycobacterial infection may be underdiagnosed if only culture-confirmed cases are included. Polymerase chain reaction provides a rapid and sensitive method to improve diagnostic accuracy. Tissue culture is crucial to determine antimicrobial susceptibility. In our study, tetracycline group of antibiotics, especially minocycline, was an effective treatment, particularly in cases caused by Mycobacterium marinum.

Intravesical injection of botulinum toxin for the treatment of overactive bladder

PURPOSE OF REVIEW

In recent years, botulinum toxin has been investigated for the treatment of various types of lower urinary tract dysfunctions. This review discusses recently published data related to the therapeutic applications of botulinum toxin in overactive bladder as well as the effects of repeated doses, cross-reactivity between different serotypes, and side effects of the toxin injection into the detrusor muscle.

RECENT FINDINGS

Botulinum toxin A has been employed initially in the treatment of neurogenic detrusor overactivity in spinal cord injured patients. Since then, several reports, including a large multicenter study, have confirmed the therapeutic effects of this neurotoxin. The application of botulinum toxin A was extended to the treatment of idiopathic detrusor overactivity and similar results were obtained. Repeated injections of botulinum toxin A had the same sustained benefit. Recently, botulinum toxin B was investigated for the treatments of both neurogenic and idiopathic detrusor overactivity as well as for the management of botulinum toxin A resistant cases.

SUMMARY

Although intradetrusal injection of botulinum toxin is not yet an approved treatment for overactive bladder, available data suggest that botulinum toxin can be a therapeutic option in patients with neurogenic and nonneurogenic detrusor overactivity who are refractory to anticholinergic medications. There is a need, however, for further investigation to determine the optimal conditions for these applications. A randomized, double-blinded, placebo-controlled trial to evaluate the therapeutic effects of botulinum toxin is under way.

Reevaluating occult incontinence

PURPOSE OF REVIEW

Occult incontinence is a controversial subject without significant exposure in the literature. Conventionally, it has been assumed to be a marker for increased risk of postoperative stress urinary incontinence (POSUI) after repair of pelvic organ prolapse. The controversy surrounds the performance of prophylactic incontinence procedures based on this assumption. Until 2004 no article in the English language had been published demonstrating an association between occult incontinence and increased risk of stress urinary incontinence after repair of severe pelvic organ prolapse in previously continent women. We will explore the evidence regarding occult incontinence, review the data on intervention trials, and address questions that remain.

RECENT FINDINGS

The limited evidence suggests 11-22% of continent patients with severe pelvic organ prolapse will develop POSUI. New evidence suggests that patients with occult incontinence are at substantially more risk. Since anti-incontinence procedures in patients with occult incontinence reduces the incidence of POSUI (to 0-15%), there appears to be some benefit from screening and intervention. Most studies on the subject are small and limited by their design. Results differ regarding whether a negative stress test can be used to rule out the risk of POSUI.

SUMMARY

Minimal existing evidence in the English language suggests that patients with occult incontinence are at increased risk of POSUI. Outcomes in occult incontinence patients undergoing repair of pelvic organ prolapse need systematic study. Until there is adequate solid evidence on the predictive values of our screening test, we cannot counsel patients regarding our ability to prevent POSUI or protect them from unnecessary procedures.

A review of laparoscopic uterine suspension procedures for uterine preservation

PURPOSE OF REVIEW

The most appropriate surgical approach for uterine preservation still remains the subject of ongoing controversy. Uterine suspension procedures can be performed abdominally, vaginally, or laparoscopically. This article focuses on the three different laparoscopic approaches of uterine suspension for uterine preservation: suspension to the round ligaments; suspension to the uterosacral ligaments; and suspension to the anterior ligament of the sacral promontory. This article reviews the published studies in the literature, analyzes the results, discusses the differences, and compares the different laparoscopic techniques.

RECENT FINDINGS

A review of the literature reveals a paucity of research studies and publications on laparoscopic uterine suspension procedures. All the published studies are small, retrospective case series or case studies. Laparoscopic ventrosuspension using the round ligaments for uterine prolapse has a reported success rate of less than 50%. The ventrosuspension procedure has a very limited role and should not be employed. In comparison, laparoscopic uterine suspension procedures have a reported success rate ranging between 81 and 100%. The newest surgical technique is the laparoscopic sacral colpohysteropexy and there is only one reported case series on this procedure. The reported success rate for the sacral colpohysteropexy is 100%.

SUMMARY

The first surgical option for uterine preservation is uterine suspension to the uterosacral ligaments. If the uterosacral ligaments cannot be identified or the uterosacral ligaments are weak and unusable, then laparoscopic sacral colpohysteropexy is a reliable second option. Uterine suspension to the round ligaments has an unacceptably high failure rate and is not an effective, durable alternative.

Physiologic role of nitric oxide and nitric oxide synthase in female lower urinary tract

PURPOSE OF REVIEW

In recent years nitric oxide (NO) has gained increasing recognition as an important neurotransmitter and cell signaling molecule with a broad range of functions in the lower urinary tract. This review discusses recently published data related to the physiologic and pathophysiologic roles of NO and nitric oxide synthase (NOS) in the female lower urinary tract.

RECENT FINDINGS

Expression of three isoforms of NOS, namely endothelial NOS, neuronal NOS and inducible NOS, has been identified in various tissues of the lower urinary tract in animals and humans. In addition to its relaxation effects on bladder and urethra, NO also serves as a neurotransmitter in the lower urinary tract. The physiologic roles of NO in overactive bladder, bladder outlet obstruction, diabetic cystopathy, interstitial cystitis, and bladder inflammation have been demonstrated.

SUMMARY

NO plays an important role in the micturition process and in disorders of the lower urinary tract. Improved understanding of the pathophysiologic role of NO/NOS system and of the L-arginine-NO-cGMP pathway may allow us to identify suitable therapeutic targets for lower urinary tract disorders. However, there is a need for further investigation to determine the precise function of NO in human lower urinary tract because most work thus far has been done in animal models.

Anabolic effects of androgens on muscles of female pelvic floor and lower urinary tract

PURPOSE OF REVIEW

This review discusses recently published data concerning the anabolic effects of androgens on muscle and the mechanism by which testosterone regulates body composition with special emphasis on the anabolic effects of androgens on the muscles of the pelvic floor and lower urinary tract.

RECENT FINDINGS

Androgens have direct anabolic effects on skeletal muscle. Testosterone increases lean body mass and decreases fat mass in a dose- and concentration-dependent fashion. The action of testosterone on muscle involves multiple mechanisms, including its effects on inducing protein synthesis, recruiting satellite cells, and modulating the commitment of pluripotent mesenchymal cells to myogenic lineage. Levator ani and other muscles of the pelvic floor and lower urinary tract are sensitive to the anabolic effects of testosterone. Androgen receptors are also expressed in the pelvic floor and lower urinary tract of both animals and humans. Anabolic effects of androgens may play an important role in the female pelvic-floor and lower-urinary-tract disorders. Furthermore, the interactions between androgen and nitric oxide synthase and arginase have been demonstrated, suggesting that androgens may also participate in modulating the physiological functions of lower urinary tract through nitric oxide.

SUMMARY

Androgens induce muscle hypertrophy and reduce fat mass. The action of androgens in the lower urinary tract and pelvic floor is complex and may depend on their anabolic effects, hormonal modulation, receptor expression, interaction with nitric oxide synthase, or a combination of these effects. Further studies are needed to determine the precise role of androgens in women with urinary incontinence and pelvic organ prolapse.

Poikiloderma-like cutaneous amyloidosis in an ethnic Chinese girl

Primary cutaneous amyloidosis is the deposition of amyloid in the skin without involvement of internal organs. It is easily diagnosed when presented in its typical manifestation. Atypical or rare clinical presentations can pose diagnostic difficulties. Poikiloderma-like cutaneous amyloidosis (PCA), a rare variant of primary cutaneous amyloidosis, was first reported in the literature in 1936 (1). It is characterised by: 1) poikilodermatous skin lesions; 2) lichenoid papules; 3) cutaneous amyloid deposit in the pigmented and lichenoid lesions; 4) light sensitivity; 5) short stature; and 6) other features such as blister formation or palmoplantar keratosis. Ogino coined the term PCA syndrome when these unusual features present early in life (2). We report a 26-year-old Chinese woman who presented with poikilodermatous skin lesions and was misdiagnosed as poikiloderma atrophica vasculare (PAV) on the basis of clinical appearance without any histological proof. The diagnosis of PCA was made after skin biopsy which showed amyloid deposits in the skin. This condition can easily be confused with other true poikiloderma skin diseases. Histology is important in confirming the diagnosis.

HIV-associated eosinophilic folliculitis in a Chinese woman: a case report and a survey in Hong Kong

This is the first survey of eosinophilic folliculitis (EF) in patients infected with the human immunodeficiency virus (HIV) in Hong Kong. The present report provides the local data on HIV-associated eosinophilic folliculitis (HIV-EF) and includes the first Chinese, heterosexual female patient with this condition. This is a retrospective study on all HIV-positive patients (n = 451) attending the outpatient clinic of the AIDS Unit in Hong Kong. Patients diagnosed as having EF with histological support were included for analysis. The data were presented by descriptive method. Three patients were identified, all of them had skin biopsies done which confirmed the diagnosis; including the female case. Recognition of HIV-EF is important because it is indicative of significant immunosuppression with risk of opportunistic infection. We concluded that HIV-EF is no longer an exclusive male disease in homosexual patients only. We expect more female patients or heterosexual subjects who are HIV positive developing this disease in the future.

Genome-wide expression monitoring in Saccharomyces cerevisiae

The genomic sequence of the budding yeast Saccharomyces cerevisiae has been used to design and synthesize high-density oligonucleotide arrays for monitoring the expression levels of nearly all yeast genes. This direct and highly parallel approach involves the hybridization of total mRNA populations to a set of four arrays that contain a total of more than 260,000 specifically chosen oligonucleotides synthesized in situ using light-directed combinatorial chemistry. The measurements are quantitative, sensitive, specific, and reproducible. Expression levels ranging from less than 0.1 copies to several hundred copies per cell have been measured for cells grown in rich and minimal media. Nearly 90% of all yeast mRNAs are observed to be present under both conditions, with approximately 50% present at levels between 0.1 and 1 copy per cell. Many of the genes observed to be differentially expressed under these conditions are expected, but large differences are also observed for many previously uncharacterized genes.

Three-dimensional finite element analysis of the effects of posts on stress distribution in dentin

A finite element analysis was conducted to study the influence of posts on dentinal stress in pulpless teeth. Three-dimensional models of an intact Chinese maxillary central incisor with and without post restoration were analyzed. When the tooth was subjected to masticatory and traumatic loads, stress distributions in dentin were similar whether or not the post was present. Maximal dentinal stresses were reduced by only 7% to 10% and 10% to 14.5%, respectively, with gold alloy and stainless steel posts. Thus the reinforcement effects from posts appeared limited in pulpless incisors.

Analysis of cholesterol in all lipoprotein classes by single vertical ultracentrifugation of fingerstick blood and controlled-dispersion flow analysis

This new, highly sensitive analytical system, based on controlled dispersion of the flowing sample, gives a rapid, continuous, and direct analysis for cholesterol in all lipoprotein classes, separated by single vertical-spin density-gradient ultracentrifugation. In this Vertical Auto Profile-II fingerstick system, designated VAP-IIfs, a narrow-bore Teflon coil serves as the reactor with no segmentation of the analytical stream by air bubbles, in contrast to the Technicon AutoAnalyzer used in the VAP-I method. Concentrations of high-, low-, intermediate-, and very-low-density lipoprotein cholesterol and lipoprotein(a) cholesterol are determined by decomposing the spectrophotometric absorbance curve for the continuous analysis of the centrifuged sample, with use of software developed in this laboratory. Total cholesterol is determined from the total area under the absorbance curve. For assaying total cholesterol, the CV between aliquots within a rotor ranged from 1.35% to 3.15%; the CV between rotors was 2.45%. Because only 18 microL of sample is required, VAP-IIfs can be readily adapted to analysis for lipoprotein cholesterol profiles in capillary blood samples. Total cholesterol values by VAP-IIfs for fingerstick and venous samples from 23 subjects agreed well: slope = 1.01 (SD 0.03), intercept = -21 (SD 51) mg/L, Sy/x = 50 mg/L, and r = 0.992. Results by VAP-IIfs also correlated highly with results for duplicate samples analyzed at the Northwest Lipid Research Laboratories.

Flow injection analysis of L-lactate with enzyme amplification and amperometric detection

A flow injection analysis method for the determination of the lactate anion with enzyme amplification and amperometric detection is described. The system utilizes an oxygen electrode for measurement of changes in the oxygen concentration in the flow stream. Two enzymes, lactate oxidase and lactate dehydrogenase, were randomly coimmobilized on aminopropyl controlled-pore glass (AMP-CPG) and packed into a reactor. beta-NADH was used as a coenzyme for the regeneration of lactate from pyruvate. The experimental conditions for the determination of the lactate anion were studied for this system by the simplex and the univariant methods. The results obtained under these two conditions were compared. The simplex experimental condition yielded a calibration curve whose linear portion had a slope that was 1.2 times greater than that of the linear portion of the curve obtained under univariant conditions. The limit of detection under simplex condition was 1.19 x 10(-7) M vs 3.29 x 10(-7) M lactate under univariant conditions. The relative standard deviation obtained for this system at 6 x 10(-6) M lactate (n = 10) was about 2.5% under simplex conditions and 3.6% under univariant maximization conditions.

In vitro propagation of human hepatitis B virus in a rat hepatoma cell line

A rat hepatoma cell line (Q7) of Morris hepatoma origin was transfected with a construct containing the tandem dimer genome of human hepatitis B virus (HBV) and the neomycin-resistant selection marker. The culture medium of several neomycin-resistant single-cell clones was found to accumulate high levels of secreted HBV surface antigen and core-related e antigen. HBV-specific replication intermediates, including relaxed circular and single-stranded DNA with a minus-strand polarity, could be found in both the intracellular fraction and the extracellular culture medium by the Southern blot procedure. One of these clones, designated Q7 HBV-21, was characterized in further detail. DNA polymerase activity was present in the virus particles produced by Q7 HBV-21 cells. Characteristic transcripts of HBV, including the 3.5-, 2.5-, and 2.1-kilobase mRNA as well as a core-gene-related transcript of 2.2 kilobases could be detected. Electron microscopic examination of the conditioned medium from Q7 HBV-21 cells identified 42-nm Dane-like particles as well as 22-nm subviral particles with a spherical or filamentous shape. This Q7 HBV-21 cell line has been maintained in the absence of neomycin for 1 year without losing the properties of HBV DNA replication and Dane-like particle production. Our results strongly suggest that the species barrier of HBV infection is at an early step of viral absorption onto or penetration into the target hepatocytes. This nonhuman system for HBV production in culture could be used to complement the human HepG2 system.

Validity domain of the weak-phase-object approximation for electron diffraction of thin protein crystals

The domain of validity of the weak-phase-object (WPO) approximation is evaluated for high-energy electrons (100 keV, 500 keV and 1 MeV) scattered by crystalline biological macromolecules. Cytochrome b5 is used as an example in which calculated dynamical diffraction intensities are used to simulate observed diffraction intensities which are then compared with intensities calculated by the weak-phase-object approximation. Three criteria of validity are used, namely the crystallographic residual (R value), the interpretability of difference Patterson maps, and the results of phasing by the heavy-atom isomorphous replacement method. The present calculations indicate that the error associated with the WPO approximation is quite acceptable up to a specimen thickness of 200 A for 100 keV electrons, which is two to four times the thickness limit for crystalline organic structures with much smaller unit-cell dimensions. An equally acceptable thickness limit at 500 keV and 1MeV is about 300-350 A.

Enantiomeric composition analysis of amphetamine and methamphetamine by chiral phase high-performance liquid chromatography-mass spectrometry

N-(Trifluoroacetyl)-l-prolyl- (N-TFA-l-prolyl-) d- and l-amphetamine diastereoisomers were separated by high-performance liquid chromatography and confirmed by an interfaced mass spectrometer system, using the commercially available N-3,5-(dinitrobenzoyl)phenylglycine chiral column. A separation factor of 1.52 and resolution of 3.8 were observed. N-TFA-l-prolyl-d- and -l-methamphetamine diastereoisomers were only partially resolved. The chiral stationary phase-solute interactions were studied by varying the mobile phase (2-propanol in hexane). Results indicate the separation mechanism proceeds via dipolar and hydrogen-bond interactions between the chiral stationary phase and the solute. A modified "dipole-stacking" model takes into account these interactions and explains the difference in separability observed for N-TFA-l-prolyl-d- and -l-amphetamine and N-TFA-l-prolyl-d- and -l-methamphetamine.

Daily rhythm in human urinary melatonin

The melatonin in urine samples from six healthy adult volunteers was concentrated on Amberlite XAD-2 resin, eluted with organic solvents, and quantitated by use of a bioassay technique (the dermal melanaphore response of larval anurans to melatonin in their bathing medium). The melatonin content of samples collected between 11 p.m. and 7 a.m. was, in each case, several times higher than that of samples collected between 7 a.m. and 3 p.m. or between 3 p.m. and 11 p.m.