344

lationship between acute reduction in circulating potassium levels and digitalis-induced arrhythmias, and the only discovered work on chronic potassium depletion in laboratory animals did not show increased sensitivity to the action of digitalis.12 Therefore, on what grounds are we entitled to teach that diuretic-induced chronic hypokalaemia in patients makes them more likely to have arrhythmias when digitalis is being given concomitantly ? Some recent experimental work helps delineate the problem. Dogs anaesthetised with sodium pentobarbitone were infused with 3H-digoxin at 20 tJ.g. per minute until atrioventricular dissociation occurred. This was chosen in preference to ventricular tachycardia, for in the presence of low plasma-potassium concentrations ventricular tachycardia is difficult to diagnose. Routine electrocardiograms and also atrial electrograms were done during the infusion of digoxin to help in the diagnosis of the arrhythmias, and plasma and tissue were taken for analysis for tritium content ten minutes after the digoxin infusion had been stopped after the first appearance of atrioventricular dissociation lasting more than 3 seconds. The control series contained 8 dogs, an acutely hypokalaemic group (glucoseinsulin infusion) had 10 dogs in it, while the chronic hypokalxmic dogs (hydrochlorthiazide plus high sodium, no potassium synthetic diet) contained 6 dogs. Although complete analysis has not been accomplished, the average plasma-potassium concentrations in these groups when the digoxin infusion was started were 4-0,2-3, and 2-6 meq. The amount of digoxin infused to produce per litre. atrioventricular dissociation was 151, 144, and 145 tJ.g. per kg. Digitalis-induced ventricular irritability appears to be induced first in the left ventricle,21 and the left ventricular myocardial digoxin content in the normal and acutely hypokalaemic groups (chronic hypokalasmia not yet analysed) at atrioventricular dissociation averaged 630 and 679 ng. per g. wet

weight.

In these experiments no evidence has come to light to support the idea that hypokalaemia, either acute or chronic, sensitises the myocardium to digoxin. Of particular importance are the chronic hypokalaemia experiments where 100 mg. hydrochlorthiazide a day and a zero potassium intake produced an average negative potassium balance of 78 meq. over a period of about ten days. This design was employed to give the nearest practical approximation to the condition of a patient on chronic diuretic therapy. As there was no evidence that those animals were more sensitive to digoxin, perhaps our teaching should be less

pragmatic. Section of Cardiology, Pennsylvania Hospital, Philadelphia, Pennsylvania 19107, U.S.A.

P. F. BINNION.

MULTIPLE SCLEROSIS SIR,—The paper by Sir Charles Symonds (Jan. 18, p. 155) raises some interesting points in comparative pathology and biochemistry. It also points out how sound scientific observations can be largely ignored in the quest for fashionable explanations of disease phenomena. Certainly Sir Charles Symonds is right to question Acheson’s statement that any relation between swayback and multiple sclerosis can be discounted. The demyelinating disease swayback is not a simple manifestation of copper deficiency. Copper and vitamin-A metabolism are closely interrelated and a decrease in bloodcopper level diminishes the liver’s capacity to store the vitamin in preparation for its many metabolic roles.22 Among these is the activation of sulphate to 3’-phospho21. 22.

Kastor, J. A., Spear, J. F., Moore, E. N. ibid. 1972, 45, 952. Owen, E. C. Fd Cosmet. Toxicol. 1965, 3, 701.

adenosine-5’-phosphosulphate, an essential step in the of the sulphatides of the medullary sheath. synthesis Owen 23 has discussed mechanisms by which copper and/or vitamin-A deficiency may interfere with sulphate metabolism and myelin integrity. Irving and Richards 2’ studied the relationship between the level of vitamin A in the diet and the incidence of demyelinated fibres in the medulla of the rat brain. Demyelination occurred at levels none of which was so low that overt signs of vitamin deficiency were produced. However, some consider that any damage to the nervous system in hypovitaminosis A is caused by skeletal dysplasia.25 Since the optimum human requirement of vitamin A is not known with any certainty, certain members of the community may be deficient in it. In his classic Nutrition and Disease, Mellanby suggested that a vitamin-A-rich diet might be of value in treating the inflammatory stage which occurs before the glial overgrowth in multiple sclerosis and produced some clinical evidence to support thiS.26 This work has never been adequately followed up and it is only recently that attention has once again been focused on nutritional influences in multiple sclerosis. 27 Many factors may operate in the development of this disease and the nutritional status of the individual may control how he responds to some of these-e.g., viral infection-and should not be neglected. As Mellanby remarked forty years ago, it is important that "... no possibility is missed of adding knowledge to the eetiology or therapeutics of an otherwise intractable disease ". Metabolic Unit, University College Hospital, London WC1E 6JJ.

J. GODFREY HEATHCOTE.

AGGREGATION OF HUMAN PLATELETS BY PLATELET-ACTIVATING FACTOR SIR,—Platelet-activating factor (P.A.F.) is a basic phospholipid from human or rabbit basophils which aggregates rabbit platelets and releases their vasoactive amines 28; rabbit P.A.F. has been implicated in deposition of immune complexes in acute serum sickness.29 The possible role of P.A.F. in human immunological diseases raises the question of its target cell. We have demonstrated its action on human platelets. Human platelets were prepared by centrifugation and washing on a cushion of red blood-cells.3O Aggregation was measured in an aggregometer; the heights of the recorded curves were expressed as arbitrary units. After aggregation, platelets were centrifuged and the serotonin content of supernatants and pellets was measured.31 The percentage of serotonin released into the supernatants was calculated. Human P.A.F. used in these experiments was a phospholipidic fraction from a silica-gel thin-layer chromatography. Typical results are given in the accompanying table. P.A.F. induced a two-stage aggregation curve; the second stage was most probably related to endogenous adenosine diphosphate (A.D.P.) release by the platelets; it was suppressed by apyrase, an A.D.P. inhibitor. A.D.P. itself induced first-stage and second-stage aggregations of the same magnitude as those observed with P.A.F. Clotting of 23. 24. 25. 26. 27.

28. 29. 30. 31.

Owen, E. C. Wld Rev. Nutr. Dietet. 1965, 5, 184. Irving, J. T., Richards, M. B. Biochem. J. 1940, 34, 198. McIlwain, H., Bachelard, H. S. Biochemistry and the C.N.S.; p. 300. London, 1971. Mellanby, E. Nutrition and Disease. Edinburgh, 1934. Millar, J. H. D., et al. Br. med. J. 1973, i, 765. Benveniste, J. Nature, 1974, 241, 581. Benveniste, J., Henson, P. M., Cochrane, C. G. J. exp. Med. 1972, 136, 1356. Bang, N. V., Heidenreich, R. O., Trygstad, C. W. Ann. N. Y. Acad. Sci. 1972, 201, 280. Weissbach, H., Andrews, E., Seligson, H. T. Standard Methods of Clinical Chemistry; vol. IV, p. 197. New York, 1963.

345 AGGREGATION OF PLATELETS BY P.A.F., A.D.P., AND THROMBIN

I

I &mid ot;

25

x

platelets

10’

with 1’5

x

were

suspended in 1 ml. of Tyrode’s solution added

10-3M calcium chloride and 360 µ.g. per ml. human

fibrinogen. t First-stage and second-stage aggregation heights.

fibrinogen by thrombin released all the serotonin from the platelets trapped in the fibrin mesh. Without fibrinogen, thrombin induced platelet aggregation and release comparable to P.A.F. and A.D.P. These results suggest that the IgE-basophil-p.A.F. system, a starter mechanism of immune-complex deposition in the rabbit, also exists in man. Its role in human immunological diseases remains to be demonstrated. Hôpital Necker, J. BENVENISTE 161 rue de Sèvres, J. P. LE COUEDIC 75730 Paris Cedex 15,

ÆTIOLOGY OF

JAMAICAN NEUROPATHY SIR,-Strokes excepted, the commonest neurological problem in Jamaica is a neuropathy, the major elements of which are damage to the pyramidal tracts and posterior columns, selective lower-motor-neurone lesions, retrobulbar neuropathy, and nerve deafness. 1-3 Although these lesions occur singly or in combination, the clinical presentation is generally in two groups-the spastic, in which pyramidaltract damage is severe, and the ataxic in which posteriorcolumn loss predominates. The aetiology of this syndrome is disputed. Though disseminated in space, the natural history of the c.N.s. lesions is not that of multiple sclerosis.,,2 The clinical picture is also compatible with syphilis, but 20-65% of patients have a normal blood serology (the incidence of a positive v.D.R.L. in the general population is 30%) and the cerebrospinal-fluid serology is normal in 75-100% of cases.1-3 Furthermore, the incidence of this neuropathy is far greater than all of the recognisable forms of neurosyphilis taken together. Of great interest is the recent description of a disorder resembling multiple sclerosis in young women with chronic biological false-positive serological tests for syphilis, characterised by pyramidal-tract damage and minimum involvement of other systems.4 Other serological abnormalities were L.E. cells, high IgM levels, and antimitoD.N.A.

antibodies

were not

tested

for, but it was suggested that this so-called " lupoid sclerosis " might be related to S.L.E. The serum of as

30% of patients with

S.L.E. shows a positive reaction.6 It is possible that the Jamaican neuropathy syndrome whether luetic in origin or not may have a similar immunological basis. Further investigation of this possibility is at present in progress.

many

as

V.D.R.L. or F.T.A.-ABS

University Hospital of the West Indies, Kingston 7, Jamaica.

W. A. WILSON G. R. V. HUGHES.

Cruickshank, E. K. West Indian med. J. 1956, 16, 233. Montgomery, R. D., Cruickshank, E. K., Robertson, W. B., McMenemey, W. H. Brain, 1964, 87, 425. 3. Rodgers, P. E. West Indian med. J. 1965, 14, 36. 4. Fulford, K. W., Catterall, R., Delhanty, J., Doniach, E., Kremer, M. Brain, 1972, 95, 373. 5. Kraus, S. J., Haserick, J. R., Lantz, M. A. New Engl. J. Med. 1970, 282, 1287. 1. 2.

RESULTS

OF

CONFIRMATORY TESTING ON 577 HEPANOSTICONPOSITIVE BLOOD-DONOR SPECIMENS

P. KAMOUN.

France.

chondrial antibodies.

HEPANOSTICON IN SCREENING FOR HBsAg SIR,—We have carried out the reversed passive haemagglutination techniquedeveloped by Schuurs and Kacaki (’ Hepanosticon ’, Organon Scientific Development Group, Oss, Holland) in parallel to counter-electrophoresis (C.E.p.)2 on 139,853 volunteer-blood-donor sera. All sera giving positive reactions were re-tested by ’Ausria-125 ’ (Abbott Laboratories), and the specificity of results obtained with this test was evaluated by neutralisation with antiHBS,3 as well as by a reversed passive haemagglutination test (’Raphadex B’) and its confirmatory anti-HB, neutralisation test.4 These independent tests for HB.Ag specificity were compared with the results obtained by

Determined by anti-HBs neutralisation test with ausria and/or raphadex B. t 2 specimens too low in titre to show 4-fold reduction by anti-HBs. t1 specimen was still positive after 3 absorptions: 1 specimen was of insufficient quantity for second absorption.

absorbing positive-reacting sera with the hepanosticon absorbent-i.e., sheep red cells coated with normal sheep IgG. 577 sera gave positive results in the hepanosticon screening-test. Confirmatory test results on these sera are shown in the accompanying table. 10 of the 255 were which found to be specimens HBsAg-specific by anti-HB;, neutralisation became negative in the hepanosticon test after absorption with the hepanosticon absorbent-a finding reported also by Schuurs and Kacaki.l Of 322 specimens found to be nonspecific on the basis of ausria and raphadex testing and anti-HBs neutralisation, 50 required two absorptions, and 3 required three absorptions with the Organon absorbent prior to turning negative. The ability of the hepanosticon test to detect HBsAgspecific specimens compared favourably with C.E.P.: 225 (0-18%), compared with 185 (0-13%) detected by the latter test-i.e., 38% additional positives. The raphadex B test, which detected 32 HBAg-specific specimens out of 20,100 volunteer donor sera compared with 31 detected by ausria 125I’4 detected 37% additional specific positives in a comparison with C.E.P. on 137,000 donor sera. The three tests thus appear essentially equal in their ability to detect HBSAg in blood-donor sera. However, our data indicate that the hepanosticon absorbent procedure is not a satisfactory test for HBsAg specificity. We agree with Reesink et al.5 that a confirmatory test based on anti-HB, neutralisation is required for this purpose. New York Blood Center, 310 East 67 Street, New York, N.Y. 10021, U.S.A.

DORIS CHICOT R. WRIGHT B. BROTMAN ALFRED M. PRINCE.

Schuurs, A. H. W. M., Kacaki, J. Vox sang. 1974, 27, 97. Alter, H. J., Holland, P. V., Purcell, R. H. J. Lab. clin. Med. 1971, 77, 1000. 3. Prince, A. M., Brotman, B., Jass, D., Ikram, H. Lancet, 1973, i, 1346. 4. Prince, A. M., Chicot, D., Wright, R., Vnek, J., Neurath, R., Lippin, A., Swiss, S., Ehrich, C. Unpublished. 5. Reesink, H. W., Duimel, W. J., Brummelhuis, H. G. L. Lancet, 1973, ii, 1351.

1. 2.