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The European Register for Specialists in Clinical Chemistry and Laboratory Medicine: guide to the Register Version 2-2003 and procedure for re-registration.
The European Communities Confederation of Clinical Chemistry and Laboratory Medicine (EC4) opened a Register for European Chemists in 1997. The operation of the Register is undertaken by a Register Committee (EC4RC). During the last 5 years more than 1,400 clinical chemists entered the register. In this article an update of the first Guide to the Register is given, based on the experience of 5 years of operation and the development of the discipline. The registration is valid for 5 years. In a second part the procedure and the conditions for re-registration are presented.
Moyamoya disease in a patient with schizophrenia.
We present the case of a 23-year-old Vietnamese male with a 2-year history of a psychotic illness marked by prominent negative symptoms, fatuousness and disturbed behavior. Neuroimaging revealed a prominent vascular flow void affecting the middle and anterior cerebral arteries, with associated increased collateral supply to the frontal cortex, consistent with Moyamoya disease. Neurological examination was unremarkable; however, neuropsychological assessment revealed significant executive dysfunction, including stimulus-driven behavior. Whilst the diagnosis of schizophrenia and Moyamoya disease may be coincidental, an interaction between the 2 diseases may have led to some of the atypical features of this case, including prominent executive dysfunction and marked sensitivity to psychotropic medication. We discuss the nature of possible interactions between the 2 conditions. This case also highlights the importance of re-evaluating patients with atypical or treatment-resistant psychoses for cerebral pathology.
Investigation of potential iatrogenic transmission of hepatitis C in Victoria, Australia.
OBJECTIVE: To determine the level of exposure to medical and surgical procedures among Australian-born patients whose mode of acquisition of the hepatitis C virus (HCV) is unknown. METHOD: Place and time of study: Melbourne, Australia, 1998-2000. DESIGN: Retrospective case series. INSTRUMENT: Structured questionnaire administered by one interviewer. SETTING: Referral centre for hepatitis C in a tertiary teaching hospital. PARTICIPANTS: Australian-born individuals persistently HCV antibody (anti-HCV) positive on at least two second-generation commercial assays. MAIN OUTCOME MEASURES: Demographic and self-reported exposure data. RESULTS: Of 135 anti-HCV positive individuals with no known mode of transmission, 54 (40%) individuals fulfilled all the entry criteria and agreed to participate. Of the 54 cases, 53 had at least one medical/surgical procedure and/or invasive dental work; 46 (85%) had dental extractions, 19 (35.2%) had complex dental work, e.g. root canal, 44 (82%) had an operation requiring general anaesthesia, 41 (75.9%) had a procedure requiring local anaesthetic, and a number of endoscopic procedures were reported: gastroscopy (n=3), colonoscopy (n=3), laparoscopy (n=4), arthroscopy (n=5), cystoscopy (n=2). CONCLUSION: We have documented exposure to medica/surgical procedures among HCV patients with no previously recognised mode of transmission. IMPLICATIONS: The findings of this study have important public health implications for current cleaning, disinfection and sterilisation procedures and protocols (or lack of these) as well as for the policies and guidelines relating to the re-use of medical equipment such as multi-dose vials, suturing material and anaesthetic circuits.
The vesicular monoamine transporter is not regulated by dopaminergic drug treatments.
The number of neuronal synaptic vesicular monoamine transporters (vesicular monoamine transporter type 2; VMAT2) has been recently proposed as an index of monoamine presynaptic terminal density. The present study investigated the possible regulation of the vesicular monoamine transporter. Rats were treated for 2 weeks with drugs known to influence dopaminergic neurotransmission, including those commonly used in the treatment of Parkinson's disease. Autoradiographic assays were performed using [3H]methoxytetrabenazine, [3H]raclopride, and [3H]WIN 35,428 ([3H]2beta-carbomethoxy-3beta-(4-fluorophenyl)tropane) to measure vesicular monoamine transporter, dopamine D2 receptor and synaptic plasma membrane dopamine re-uptake site bindings, respectively. None of the drug treatments significantly modified levels of vesicular monoamine transporter binding. In contrast, both dopamine D2 receptors and dopamine re-uptake sites were altered by some of the treatment regimens. These data extend preliminary results that suggest the vesicular monoamine transporter is not easily regulated and confirm the plasticity of dopamine D2 receptors and the dopamine re-uptake site. Measures of striatal vesicular monoamine transporter density may, thus, provide objective estimates of monoaminergic innervation in neurodegenerative diseases, unaffected by the use of symptomatic therapies.
The measurement of corneal epithelial thickness in response to hypoxia using optical coherence tomography.
PURPOSE: To determine if corneal epithelial thickness increases in association with corneal edema induced by wearing soft contact lenses during eye closure. DESIGN: Experimental study. METHODS: One eye (randomly selected) of twenty noncontact lens wearers (10 males and 10 females, age 35.6 +/- 9.6 years) was patched during 3 hours of soft contact lens (SCL) wear and the contralateral eye acted as a control. Corneal and epithelial thickness of both eyes was measured before and after SCL wear using optical coherence tomography (OCT). RESULTS: Immediately after contact lens removal, total corneal thickness was increased significantly by 13.8 +/- 2.3% (mean +/- SD) compared with baseline (P <.0001, paired t test) and after 100 minutes was still 4.5 +/- 2.3% thicker than baseline (P <.0001, paired t test). The control eyes showed no change in total corneal thickness (P >.05, paired t test). Immediately after contact lens removal, corneal epithelial thickness was increased by 1.7 +/- 4.8%, but this change was not statistically significant (P >.05, paired t test). Following contact lens removal, epithelial thickness changed significantly (Repeated measure analysis of variance [Re-ANOVA]: F((7,133)) = 4.91, p(H-F) < 0.001) over the next 100 minutes with thinning recorded at 60, 80, and 100 minutes (P <.05, paired t test). There was no significant change over time in epithelial thickness of the control eyes (Re-ANOVA: F(4, 76) = 0.91, p(H-F) = 0.464). CONCLUSION: OCT demonstrated that corneal epithelial thickness does not increase in response to hypoxia from SCL wear and eye closure, in contrast to a significant increase in total corneal thickness.
Plasticity and cytokinetic dynamics of the hair follicle mesenchyme: implications for hair growth control.
The continuously remodeled hair follicle is a uniquely exploitable epithelial-mesenchymal interaction system. In contrast to the cyclical fate of the hair follicle epithelium, the dynamics of the supposedly stable hair follicle mesenchyme remains enigmatic. Here we address this issue using the C57BL/6 hair research model. During hair growth, increase in total follicular papilla size was associated with doubling of papilla cell numbers, much of which occurred before intra-follicular papilla cell proliferation, and subsequent to mitosis in the proximal connective tissue sheath. This indicates that some papilla cells originate in, and migrate from, the proliferating pool of connective tissue sheath fibroblasts. Follicular papilla cell number and total papilla size were maximal by anagen VI, but intriguingly, decreased by 25% during this period of sustained hair production. This cell loss, which continued during catagen, was not associated with intra-follicular papilla apoptosis, strongly indicating that fibroblasts migrate out of the late anagen/early catagen papilla and re-enter the proximal connective tissue sheath. Low-level apoptosis occurred only here, along with the "detachment" of cells from the regressing connective tissue sheath. Thus, the hair follicle mesenchyme exhibits significant hair cycle-associated plasticity. Modulation of these cell interchanges is likely to be important during clinically important hair follicle transformations, e.g. vellus-to-terminal and terminal-to-vellus during androgenetic alopecia.
The practice of clinical chemistry in the European Union.
The European Communities Confederation of Clinical Chemistry has been actively engaged in raising the level of clinical chemistry in the European Union. Closer contacts between the national societies for clinical chemistry have resulted in more comparable programs for postgraduate training of clinical chemists, closer similarity of contents and practice of the profession in the different countries, and the official registration of professionals. This article reviews some of the characteristics of professional organisation, practice, and regulation in the fifteen European Union countries. Many similarities appear. In half of the countries microbiology, blood-banking and transfusion medicine fall within the domain of clinical chemistry. The minimum number of years for training (university and postgraduate) is eight, but in practice this will extend to 10 or more years. Official regulation of the profession by law exists in a minority of countries. Continuing education and re-registration have not been officially instituted yet in any country, but these issues will be the next steps forward. In those countries that prepare themselves for entering the European Union, training and practice of clinical chemistry are moving towards the common standards of the European Communities Confederation of Clinical Chemistry.
Neuroanatomical abnormalities before and after onset of psychosis: a cross-sectional and longitudinal MRI comparison.
BACKGROUND: Psychotic disorders, such as schizophrenia, are associated with neuroanatomical abnormalities, but whether these predate the onset of symptoms or develop progressively over the course of illness is unclear. We investigated this issue with MRI to study people with prodromal symptoms who are at ultra high-risk for the development of psychosis. METHODS: We did two comparisons, cross-sectional and longitudinal. For the cross-sectional comparison, 75 people with prodromal signs of psychosis were scanned with MRI. After at least 12 months of follow-up, 23 (31%) had developed psychosis and 52 (69%) had not. Baseline MRI data from these two subgroups were compared. For the longitudinal comparison, 21 of the ultra high-risk individuals were scanned again with MRI after at least 12 months. Ten of these had developed psychosis and 11 had not. MRI data from baseline and follow-up were compared within each group of people. FINDINGS: In the cross-sectional comparison, compared with people who did not develop psychosis, those who did develop the disorder had less grey matter in the right medial temporal, lateral temporal, and inferior frontal cortex, and in the cingulate cortex bilaterally. In the longitudinal comparison, when re-scanned, individuals who had developed psychosis showed a reduction in grey matter in the left parahippocampal, fusiform, orbitofrontal and cerebellar cortices, and the cingulate gyri. In those who had not become psychotic, longitudinal changes were restricted to the cerebellum. INTERPRETATION: Some of the grey-matter abnormalities associated with psychotic disorders predate the onset of frank symptoms, whereas others appear in association with their first expression.
Effect of peri-operative red blood cell transfusion on 30-day and 1-year mortality following coronary artery bypass surgery.
OBJECTIVE: The purpose of this study was to examine the effect of peri-operative red blood cell (RBC) transfusion on 30-day and 1-year mortality following coronary artery bypass grafting (CABG). METHODS: We retrospectively analysed 3024 consecutive patients who underwent isolated CABG between January 1999 and December 2001. Patient records were linked to the National Strategic Tracing Service, which records all mortality in the UK. Thirty-day and 1-year mortality were derived from Kaplan-Meier curves. Confounding variables were controlled for by constructing a propensity score for the probability of receiving a transfusion from core patient characteristics including the lowest recorded laboratory haemoglobin (LL Hb) from a clinical chemistry database (C statistic 0.81). The propensity score and the comparison variable (transfusion versus no transfusion) were included in a Cox proportional hazards analysis, allowing calculation of adjusted hazard ratios (HR) and Kaplan-Meier survival curves. RESULTS: Nine hundred and forty (31.1%) patients received RBC transfusion during or within 72h of surgery. Predictors of the need for transfusion were LL Hb and lower body mass index, use of cardiopulmonary bypass, female sex, number of grafts, renal dysfunction, increased age, extent of disease, and prior CABG; these factors were all included in the propensity score. After 1-year of follow-up, 122 (4.03%) deaths occurred. The crude HR for 1-year mortality in patients transfused was 3.0 (P<0.001). After adjusting for the propensity score, re-operation for bleeding, peri-operative blood loss and post-operative complications, the adjusted 30-day mortality was 1.9% in transfused patients compared to 1.1% in patients not transfused (P<0.05). The adjusted HR for 1-year mortality in patients transfused was 1.88 (P<0.01). CONCLUSIONS: Peri-operative RBC transfusion after CABG is associated with an increased risk of mortality during a 1-year follow-up period, with a large proportion of deaths occurring within 30-days.
Cerebral relapse of metastatic gastrointestinal stromal tumor during treatment with imatinib mesylate: case report.
BACKGROUND: The management of unresectable or metastatic gastrointestinal stromal tumors (GISTs) has previously been difficult as they are resistant to conventional chemotherapy and radiation. The development of imatinib mesylate has made a major impact on the management of advanced GISTs. It is apparent that there are sanctuary sites such as the central nervous system where imatinib does not achieve adequate concentrations. We describe the case of a man with metastatic GIST who experienced multiple cerebral relapses of disease while systemic disease progression appeared to be controlled by imatinib. CASE PRESENTATION: A 47-year-old man presented in July 1999 with a jejunal GIST with multiple hepatic metastases. The jejunal primary was resected and after unsuccessful cytoreductive chemotherapy, the liver metastases were also resected in December 1999. The patient subsequently relapsed in August 2001 with symptomatic hepatic, subcutaneous gluteal, left choroidal and right ocular metastases all confirmed on CT and PET scanning. Biopsy confirmed recurrent GIST. MRI and lumbar puncture excluded central nervous system involvement. The patient was commenced on imatinib 400 mg bd in September 2001 through a clinical trial. The symptoms improved with objective PET and CT scan response until December 2002 when the patient developed a right-sided foot drop. MRI scan showed a left parasagittal tumor which was resected and confirmed histologically to be metastatic GIST. Imatinib was ceased pre-operatively due to the trial protocol but recommenced in February 2003 on a compassionate use program. The left parasagittal metastasis recurred and required subsequent re-excision in September 2003 and January 2004. Control of the systemic GIST was temporarily lost on reduction of the dose of imatinib (due to limited drug supply) but on increasing the dose back to 800 mg per day, systemic disease was stabilized for a period of time before generalised progression occurred. CONCLUSION: This case illustrates that the brain can be a sanctuary site to treatment of GISTs with imatinib. Maintaining dosing of imatinib in the face of isolated sites of disease progression is also important, as other metastatic sites may still be sensitive.
Extracorporeal shock wave lithotripsy combined with litholytic therapy in the treatment of patients with symptomatic gallstones--the Melbourne experience.
OBJECTIVE: To investigate the role of extracorporeal shock wave lithotripsy using the Dornier MPL9000 lithotripter and adjuvant litholytic therapy in the treatment of symptomatic gallbladder stones. PATIENTS AND METHODS: Between August 1989 and March 1991, 399 patients had their one to three gallbladder stones fragmented by the Dornier MPL9000 lithotripter. Chenodeoxycholic acid alone was used as adjuvant litholytic therapy in the majority. A minority received a combination of chenodeoxycholic acid and ursodeoxycholic acid or ursodeoxycholic acid alone. Patients who died, had cholecystectomies or failed to complete the treatment program were excluded from analysis, leaving a cohort of 287 patients with a follow-up of at least 12 months. This cohort comprised 173 patients with single small stones (20 mm or less in diameter), 32 patients with single large stones (21 mm to 30 mm in diameter) and 82 patients with two to three stones. OUTCOME MEASURES: Patients were followed up by repeated ultrasound examination to monitor the disappearance of fragments from the gallbladder. Stone-free rates, recurrences and complications of treatment were determined. RESULTS: The stone-free rate 12 months after treatment was 37.6% for patients with a single small stone, 3.1% for patients with a single large stone and 18.3% for patients with two to three stones. Of 70 patients with a single small stone who had become stone free at some time during the 12 months after treatment, five (7.1%) experienced recurrence, as did one of the 16 patients (6.9%) with two to three stones. Some 179 patients (44.9%) experienced biliary colic after lithotripsy. Most attacks were mild. Eleven patients (2.8%) developed cholecystitis and nine (2.3%) became jaundiced. Five patients (1.3%) suffered from pancreatitis, of whom one died from severe necrotising pancreatitis. Treatment mortality was 0.25%. Cholecystectomy was needed in 44 patients (11.9%). CONCLUSIONS: Only about 15%-20% of all patients with symptomatic gallbladder stones are suitable for lithotripsy. In this study, only about 28% were stone free after 12 months. As the gallbladder is not removed, stones may re-form. Laparoscopic cholecystectomy and open cholecystectomy by comparison will produce a "stone-free state" in 100% of patients, no matter how many stones are present in the gallbladder, their size, or whether the gallbladder is non-functioning. Consequently, lithotripsy and litholytic therapy are now reserved for those few patients who are unable to tolerate general anaesthesia and cholecystectomy and those who refuse surgery. Even in centres showing the most favourable results, lithotripsy and litholytic therapy will have at best a minor role to play in the overall management of symptomatic gallbladder stones.
Mumps orchitis in the non-immune postpubertal male: a resurgent threat to male fertility?
OBJECTIVE: To report clinical findings associated with an increased incidence of mumps orchitis in Liverpool, UK, as in the last 2 years there has been a four-fold increase in the number of notified viral mumps cases in the UK. PATIENTS AND METHODS: In the 8 months before April 2005, patients presenting to the Accident and Emergency/Urology Departments of the Royal Liverpool University Hospital with a diagnosis of epididymo-orchitis were identified from the emergency urological admission database. RESULTS: Of 195 males presenting with an acute history of testicular pain and swelling, 25 gave a history of mumps parotitis 4-11 days earlier. Three had bilateral orchitis and two needed scrotal exploration to exclude torsion. Scrotal ultrasonography findings varied from increased vascularity to abnormal testicular echo texture. Treatment included analgesia, scrotal support, re-hydration and broad-spectrum antibiotics. Of the 10 patients followed-up to date, four had testicular abnormalities; one had persistent testicular pain, one a change in testicular consistency, one a noticeably reduced size of one testis, and one significant testicular atrophy. CONCLUSION: As postpubertal mumps in males is associated with a 40% incidence of orchitis, parents should be made aware that failing to immunize their children threatens the future fertility of their sons. Young men not immunized as children should be counselled and offered urgent vaccination. Clinicians should be aware that epididymo-orchitis may be secondary to mumps infection even with no history or clinical evidence of parotitis.
Seven-year outcome in the RITA-2 trial: coronary angioplasty versus medical therapy.
OBJECTIVES: This study was designed to compare the long-term consequences of percutaneous transluminal coronary angioplasty (PTCA) and continued medical treatment. BACKGROUND: The long-term effects of percutaneous coronary intervention need evaluating, especially in comparison with an alternative policy of continued medical treatment. METHODS: The Second Randomized Intervention Treatment of Angina (RITA-2) is a randomized trial of PTCA versus conservative (medical) care in 1,018 patients considered suitable for either treatment option. Information on clinical events, interventions, and symptoms is available for a median seven years follow-up. RESULTS: Death or myocardial infarction (MI) occurred in 73 (14.5%) PTCA patients and 63 (12.3%) medical patients (difference +2.2%, 95% confidence interval -2.0% to +6.4%, p = 0.21). There were 43 deaths in both groups, of which 41% were cardiac-related. Among patients assigned PTCA 12.7% subsequently had coronary artery bypass grafts, and 14.5% required additional non-randomized PTCA. Most of these re-interventions occurred within a year of randomization, and after two years the re-intervention rate was 2.3% per annum. In the medical group, 35.4% required myocardial revascularization: 15.0% in the first year and an annual rate of 3.6% after two years. An initial policy of PTCA was associated with improved anginal symptoms and exercise times. These treatment differences narrowed over time, mainly because of coronary interventions in medical patients with severe symptoms. CONCLUSIONS: In RITA-2 an initial strategy of PTCA did not influence the risk of death or MI, but it improved angina and exercise tolerance. Patients considered suitable for PTCA or medical therapy can be safely managed with continued medical therapy, but percutaneous intervention is appropriate if symptoms are not controlled.
Objective measurements of corneal light-backscatter during corneal swelling, by optical coherence tomography.
PURPOSE: To demonstrate that corneal light-backscatter can be measured objectively during corneal swelling by optical coherence tomography (OCT). METHODS: One eye (randomly selected) of 20 non-contact-lens wearers (10 men and 10 women; mean age, 35.6 +/- 9.6 years) was patched during 3 hours of soft contact lens (SCL) wear. The contralateral eye acted as the control. Central corneal images were captured before and after SCL wear at 20-minute intervals over 100 minutes using optical coherence tomography (OCT) to obtain corneal thickness and light-backscatter profiles. OCT backscattered light of the epithelial layer (decided by the thickness measurements) and 10 equally divided layers of the remaining cornea were analyzed with a custom software program. Two baseline measurements were taken at different visits before lens wear to test the repeatability of light-backscatter measurements. RESULTS: From two baseline measurements, repeated measurements showed good repeatability of normalized backscatter results. Immediately after contact lens removal, total central corneal thickness increased significantly by 13.8% +/- 2.3% (mean +/- SD) compared with baseline (P = 0.0001, paired t-test) and then decreased during the deswelling course. Corneal backscattered light changed significantly (repeated-measures ANOVA [Re-ANOVA]: F((50, 950)) = 2.22, P = 0.0001) after lens wear, and a significant increase in backscatter was found in the epithelial layer (36.4%) and the most posterior corneal layer (35.6%) immediately after lens removal (post hoc test, P = 0.005). There was a strong correlation (r = 0.9375, P < 0.05) between the change in backscatter and corneal swelling during the deswelling period. The backscatter recovery rate was approximately the same for both epithelial and posterior layers after lens removal. CONCLUSIONS: Light-backscattering analysis with OCT seems to be a promising and repeatable method of objectively measuring corneal backscatter. This study has demonstrated that corneal backscattered light increased in the anterior and posterior layers of the cornea during corneal swelling induced by contact lens wear and eye closure.
Evidence for cortical encoding specificity in episodic memory: memory-induced re-activation of picture processing areas.
Functional magnetic resonance imaging (fMRI) was used to examine whether neural pathways used to encode pictures into memory were re-activated during retrieval of those memories. At encoding, subjects semantically classified common objects presented as pictures or words. At retrieval, subjects performed yes/no recognition memory judgments on words that had been encoded as pictures or as words. The retrieval test probed memory for the encoded item, but not memory for the modality of the encoded item (picture/word). Results revealed that a subset of the brain regions involved specifically in encoding of pictures were also engaged during recognition memory for the encoded pictures. Specifically, encoding of pictures relative to words engaged bilateral extrastriate visual cortex, namely fusiform, lingual, middle occipital, and inferior temporal gyri (Broadman area (BA) 18/19/37). Recognition memory judgments about words that were encoded as pictures relative to those that were encoded as words activated fusiform and inferior temporal gyri primarily in the left hemisphere. Thus, cortical areas originally involved in perception of a visual experience become part of the long-term memory trace for that experience. These findings suggest a neural basis for encoding specificity and transfer appropriate processing in human memory.
The lysosomal cysteine protease cathepsin L regulates keratinocyte proliferation by control of growth factor recycling.
Mice deficient for cathepsin L (CTSL) show epidermal hyperplasia due to a hyperproliferation of basal keratinocytes. Here we show that the critical function of CTSL in the skin is keratinocyte specific. This is revealed by transgenic re-expression of CTSL in the keratinocytes of ctsl-/- mice, resulting in a rescue of the ctsl-/- skin phenotype. Cultivation of primary mouse keratinocytes with fibroblast- and keratinocyte-conditioned media, as well as heterologous organotypic co-cultures of mouse fibroblasts and human keratinocytes, showed that the altered keratinocyte proliferation is caused primarily by CTSL-deficiency in keratinocytes. In the absence of EGF, wild type and CTSL-knockout keratinocytes proliferate with the same rates, while in presence of EGF, ctsl-/- keratinocytes showed enhanced proliferation compared with controls. Internalization and degradation of radioactively labeled EGF was identical in both ctsl-/- and ctsl+/+ keratinocytes. However, ctsl-/- keratinocytes recycled more EGF to the cell surface, where it is bound to the EGF-receptor, which is also more abundant in ctsl-/- cells. We conclude that the hyperproliferation of keratinocytes in CTSL-knockout mice is caused by an enhanced recycling of growth factors and growth factor receptors from the endosomes to the keratinocyte plasma membrane, which result in sustained growth stimulation.
Acyl CoA:retinol acyltransferase (ARAT) activity is present in bovine retinal pigment epithelium.
Visual perception is mediated by a family of G protein-coupled receptors called the opsins. The light-absorbing chromophore in most opsins is 11-cis-retinaldehyde, which is isomerized to all-trans-retinaldehyde upon absorption of a photon. Restoration of light sensitivity to the photobleached opsin requires chemical re-isomerization of the chromophore. This is carried out by an enzymatic pathway called the visual cycle in retinal pigment epithelial cells. The isomerase in this pathway uses fatty-acyl esters of all-trans-retinol as substrate. A retinyl-ester synthase that produces these esters, called lecithin:retinol acyltransferase (LRAT), has been extensively characterized. Based on prior biochemical studies and the phenotype in lrat(-/-) knockout mice, it has been assumed that LRAT is the sole or dominant retinyl-ester synthase in the retinal pigment epithelium. Here we demonstrate the presence of a second ester synthase activity in these cells called acyl CoA:retinol acyltransferase (ARAT). We show that this activity uses palmitoyl coenzyme A as an acyl donor, unlike LRAT which uses phosphatidylcholine. Similar to LRAT, ARAT esterifies both all-trans-retinol and 11-cis-retinol. LRAT and ARAT are both potently inhibited by the retinyl-ester analog, all-trans-retinylbromoacetate, but only ARAT is inhibited by progesterone. Unexpectedly, the maximum turnover rate (V(max)) of ARAT was similar to that of LRAT. However, the Michaelis constant (K(M)) of ARAT was 10-fold higher than the K(M) of LRAT for all-trans-retinol. These observations suggest that ARAT may complement LRAT to provide additional retinyl-ester synthase activity under conditions of high all-trans-retinol. These conditions occur in the retina following exposure to bright light.