LYSOLECITHIN AND RABBIT PLATELETS

629 LYSOLECITHIN AND RABBIT PLATELETS SIR,-Mr. Rutty and Mr. Vine (Jan. 25, p. 206) have shown that rabbit platelets behave electrophoretically like human platelets in response to adenosine diphosphate (A.D.P.) and noradrenaline. After induced thrombosis, rabbit platelets become differentially more sensitive to A.D.P. than to noradrenaline in patients with arterial diseaseand with multiple sclerosis,2 and in women taking oral contraceptives.3 One of us has jointly shown 4 that in patients with arterial disease and in women on oral contraceptives this abnormal behaviour pattern is the result of a plasma-lipid disturbance, and that the active plasma fraction is a low-density lipoprotein lecithin. This is believed to be converted to a lysolecithin by a labile plasma enzyme. (A similar type of reaction has been observed in serum by Adlkofer et al. 5.) These results have recently been confirmed in vitrousing synthetic lecithin and lysolecithin. We have therefore studied the effects of lysolecithin on the rabbit’s cerebral cortical vessels using the procedure developed by Honour and Mitchell.7 When a cortical artery is nipped hard by forceps a white thrombus forms at the site, grows, and becomes detached as an embolus-a process which occurs regularly for several hours. A less severe injury (a minor injury) is not followed by a white thrombus, but application of A.D.P. to the site produces a white thrombus which becomes detached as an embolus. If concentrations of A.D.P. are successively reduced there comes a point when no thrombus forms. This end-point is replicable. The minimum concentration of A.D.P. required to produce a white body is usually of the order of 0-4-0-8 mg. per 100 ml. In six experiments, when a solution of lysolecithin (KochLight, from egg lecithin, 1-1000 mg. per 100 ml. of 0-9% saline) was dropped on to the surface of the brain where a minor injury had been made to a cortical artery, the injury site reacted by intense vasoconstriction and formation of a single white thrombus. Later applications of lysolecithin failed to reactivate the site, but A.D.P. always produced a white body. In two instances minor injuries were converted to major ones by lysolecithin (1 mg. per 100 ml.). The sites continued to produce white bodies for up to an hour at intervals of 2-3 minutes, but could not be reactivated by further applications of lysolecithin. In four experiments intravenous infusions of lysolecithin at 1 ml. per minute, using 10-100 mg. per 100 ml., for up to an hour by jugular cannulation failed to affect the " endpoint " for A.D.p.-induced white-body formation. Retrograde infusion of lysolecithin (52 mg., 1 mg. per ml., over 45 minutes) in one rabbit through a central arterial cannula also did not affect this end-point. When lysolecithin infusion was stopped, and 0-9% saline substituted, white bodies produced by A.D.P. were considerably larger than those induced by A.D.P. during the infusion. In one experiment low-density lipoproteins (density 1-006-1-063) were obtained by preparative ultracentrifugation8 of the platelet-poor plasma from 40 ml. whole blood of a subject with ischxmic heart-disease. Similar lipoproteins were obtained from an age-matched control with no clinical evidence of arterial disease. These were freed from excess inorganic ions by passage through ’Sephadex G.50’, as described previously. Neither of these preparations produced a white body when applied topically, or affected the A.D.P. end-point when infused intravenously by jugular cannulation. Further work using low-density lipoproteins is now in progress. These results seem to indicate that topically applied Hampton, J. R., Mitchell, J. R. A. Lancet, 1966, ii, 764. Bolton, C. H., Hampton, J. R., Phillipson, O. T. ibid. 1968, i, 99. Bolton, C. H., Hampton, J. R., Mitchell, J. R. A. ibid. p. 1336. Bolton, C. H., Hampton, J. R., Mitchell, J. R. A. ibid. 1967, ii, 1101. Adlkofer, F., Schiebel, W., Ancker, E., Ruhenstroth-Bauer, G. HoppeSeyler’s Z. physiol. Chem. 1968, 349, 417. 6. Hampton, J. R., Bolton, C. H. (in the press). 7. Honour, A. J., Mitchell, J. R. A. Br. J. exp. Path. 1964, 45, 75. 8. de Lalla, O. F., Gofman, J. W. in Methods of Biochemical Analysis (edited by D. Glick); p. 459. New York, 1945. 1. 2. 3. 4. 5.

may deplete the injured ve’ssel wall of some material which causes vasoconstriction and/or white-body formation. This material is not replenished. In these circumstances, however, A.D.P. is still able to cause white-body formation. The possible role of lysolecithin as a lytic agent causing irreversible cellular damage to the vessel wall, and releasing A.D.P. or a similar compound, cannot be excluded.

lysolecithin

The failure of low-density lipoprotein to produce white bodies when applied topically, or affect A.D.P. " end-point " when infused, could be due to a species difference in lipoprotein composition between man and rabbit, but in view of the work of Mr. Rutty and Mr. Vine this is less likely. Farbiszewski and Worowski 9 have recently shown that, in vitro, platelet aggregation by A.D.P. and platelet adhesiveness are increased by P (low-density) lipoproteins from both rabbits and man. The permeability of the rabbit’s vessel wall to human low-density lipoproteins might be a decisive factor, as might the rate of metabolism of human lipoproteins in the rabbit. C. H. BOLTON Department of the A. J. HONOUR Regius Professor of Medicine, G. W. PICKERING. Radcliffe Infirmary, Oxford.

VARIATIONS OF BLOOD-PRESSURE SIR,-Imust hasten to disarm Professor MacGowan’s very reasonable criticism last week (p. 572). All the measurements of blood-pressure in my investigation (Feb. 22, p. 391) were made using the right arm. I am sorry this was not stated. Department of Pharmacology, Hospital Medical College,

London

London E.1.

J. F. DUNNE.

HUMIDIFICATION OF INSPIRED AIR SIR,-Dr. Wright 10 correctly points out that my heated humidification device 11 is dangerous if any breakdown should occur in communication between the temperature sensor at the patient and the heater. The safety measures in the apparatus were not described in detail, and some changes has been made in the prototype to ensure that dangerously high temperatures cannot reach the patient. The heating coil is switched off if the temperature sensor : (1) is not correctly placed in the control box; (2) is not correctly placed in the nose-piece or the respirator tube; (3) is damaged, leading either to separation or short-circuiting of the sensor leads. Furthermore, the performance of the humidifier has been changed: the water temperature in the humidifier varies only between 58°C and 60°C when flows of 10, 20 and 30 litres per minute are used, and is 68°C at a flow of 5 litres per minute. From a bacteriological point of view this is important, since growth of pathogens is inhibited when the water temperature is around 60°C and above. The only precaution is that the flow must not be stopped while the heating coil is switched on. I hope that Dr. Wright will agree that the humidifier, with the improvements mentioned, cannot be considered as dangerous. The heated nebuliser which Dr. Wright has used probably delivers an aerosol saturated at 37°C, corresponding to 44 mg. of water per litre of gas, but the exact water content was not measured. Nebulisers which work by producing a dense mist, may, when measured, deliver only 20 mg. of water per litre of gas. Dr. Wright’s figures for his nebuliser 12 show that when not heated it delivers 33 mg. of water per litre of gas. The comfort range of gas temperature when using high flows into one nostril seems to be rather broad-32-39°C, with an optimum of 35-36°C. The discomfort for the patient in breathing a cold aerosol is greatly diminished with the 30°C aerosol used by Dr. Wright. Certainly humidification can be 9. 10. 11. 12.

Farbiszewski, R., Worowski, K. J. atheroscler. Wright, B. M. Lancet, 1968, ii, 1392. Lomholt, N. ibid. p. 1214. Wright, B. M. ibid. 1958, ii, 24.

Res.

1968, 8, 988.