Correspondence DIFFERENTAL EFFECTS OF FLUTICASONE PROPIONATE ON ALLERGEN-EVOKED BRONCHOCONSTRICTION AND INCREASED URINARY LEUKOTRIENE E 4 EXCRETION To the Editor: We read with interest the paper by O'Shaughnessy and colleagues which recently appeared in the Review (Am Rev Respir Dis 1993; 147:1473-7). The paper deals with the effect of fluticasone propi- onate pretreatment on the increased urinary excretion of leu- kotriene E 4 after immunologic challenge in atopic subjects. Al- though the paper presents interesting data as well as an exhaustive discussion, there is a point that needs to be clarified and dis- cussed. Throughout the entire paper, beginning with the title, the authors refer to "allergen evoked ... increased urinary leukotriene E 4 excretion;" several groups have, in fact, reported that allergen challenge is accompanied by a raise in urinary LTE 4 (u-LTE 4 ) con- centration. Nevertheless, the authors fail to show any data sup- porting the evidence that they are indeed measuring increased urinary LTE 4 concentrations. In fact there are no data concerning the prechallenge values of u-LTE 4 • This is of critical importance in light of the fact that the geometric mean of post-challenge u-LTE 4 concentrations reported in the present paper (18.4 ng/mmole cre- atinine) is even lower than the basal values for either healthy con- trols (23.8 ng/mmolecreatinine) or atopic subjects (23.5 ng/mmole creatinine) as published by one of the authors in Lancet 1989; 1:584-8. In this paper, the values reported for u-LTE 4 after anti- gen challenge raised to 153.7 ng/mmole creatinine. The authors refer to the Lancet paper several times but do not comment on this discrepancy. Furthermore, after a careful reading of the "Urine Collections and LTE 4 Analysis" paragraph in the METHODS section, we have concluded that the authors estimate retention time and recovery of u-LTE 4 based on the liquid scintillation counting of 250 dpm of tritium. This is the result of 5,000 (dpm added to 20 ml of urine) divided by 4 (5 ml urine samples are extracted) multiplied by 60% (the average recovery), divided by 3 (the authors use 1/3 of each reconstituted HPLC fraction for liquid scintillation counting). Con- sidering that this estimate may further be affected by several fac- tors (LTE 4 splitting in two vicinal 2 ml HPLC fractions; recovery of this system has been reported by the same authors to be 40% in J Allergy Clin Immuno/1992;89:575-83), it appears that the use of 3H-LTE 4 for recovery correction may lower measurement preci- sion rather than improve accuracy. According to the method as described in the J Allergy Clin Im- munol, the authors use 3H-LTC 4 as tracer for radioimmunoassay of LTE 4 and quantify samples against a LTC 4 standard curve. It would be interesting to know how values for LTE 4 are then extrapo- lated; if the transformation is based on the cross-reactivity reported for the antibody with LTE 4 , it is important to test parallelism of curves obtained using LTC 4 or LTE 4 as standards. Displacement curves of sulfidopeptide leukotrienes from antibodies showing good cross-reactivities for LTC 4 , LTD 4 and LTE 4 , usually do not show the same slope; quantitation as described would therefore result inaccurate. In light of the criticisms raised, it appears of vital importance to see if the post-challenge values reported are indeed reflecting increased urinary LTE 4 excretion; the authors ehould therefore measure basal values for the atopic subjects studied and, in case of statistically significant difference with post-challenge, discuss differences with previous data. ANGELO SALA GIANCARLO FOLCO Centro di Studio e Ricerca di Farmacologia Cardiopolmonare Sperimentale Universita degli Studi di Milano Milan, Italy From the Authors: We thank Drs. Sala and Folco for their comments on our paper. As I am sure they will appreciate, the assay we have used for LTE 4 has undergone continual revision since we first published it in 1987 (1). Most importantly, we no longer use a commercial kit (Amer- sham International, Amersham, UK), but have resorted to an in- house antibody raised to LTE 4 • This has allowed us to use an LTE 4 standard curve directly without the need to extrapolate from an LTC 4 one. As rightly pointed out, the latter type of extrapolation can be prone to error and we were particularly concerned that our own estimates of the cross-reactivity of the antibody in the commercial kit differed from those supplied by the manufacturer. The effect of these alterations has been to generally lower the values for assayable LTE 4 with the consequencethat our original values for baseline urinary LTE 4 (2) cannot be directly compared with those reported in our current paper. The allergen evoked rise in urinary LTE 4 is also sufficiently well established both in our hands and others (3) that we feel it is reasonable to omit the additional labor and costs of measuring baseline values in every study to ensure that a rise has actually taken place. Regarding the use of the [3H]-LTE 4 internal standard, it is true that recovery depends on scintillation counting of perhaps only a few hundred dpm. The error involved in measuring this is, how- ever, considerably less than the two- to threefold variability in LTE 4 recovery which it corrects for. With an intra- and interassay vari- ability of <200/0, there can be no doubt that this internal standardi- zation actually increases and not decreases the precision of the assay. KEVIN M. O'SHAUGHNESSY Department of Clinical Pharmacology Royal Postgraduate Medical School Hammersmith Hospital University of London London, UK 1. Richmond RR, Turner NC, Maltby NH et al. Single step procedure for the extraction andpurification of leukotrienes B 4 , C 4 and 0 4 - J Chroma- tog 1987;417:241-51. 2. Taylor GW, Taylor IK, BlackP et al. Urinary leukotriene E 4 afterantigen challenge and in acute asthma andallergic rhinitis. Lancet 1989;1:584-8. 3. Taylor IK. Release of urinary leukotriene E 4 in asthmatic subjects: A re- view. In: Samuelson B, Dahl SE, Fritsch E, Hedquist P, eds. Advances in Prostaglandins & Thromboxane Res, 1992; 21. Raven Press. INHALED CORTICOSTEROIDS IN ASTHMA To the Editor: The report by Drs. Barnes and Pedersen on the workshop on "The Efficacy and Safety of Inhaled Corticosteroids in Asthma" (Am Rev