The sedimentation rate and fragility of human erythrocytes in vitro after exposure to lead chloride.

One important contributory factor in producing anaemia in lead poisoning in human subjects is undoubtedly the inhibition of the biosynthesis of haem in erythroid bone marrow cells (Eriksen, 1955). To what extent a haemolytic action of lead participates has been the subject of much experimental study. McFadzean and Davis (1949) demonstrated more abundant stippled cells in the bone marrow of leadpoisoned guinea-pigs than in the peripheral circulation, such cells being rapidly and preferentially taken up by the spleen. The interpretation of the 'data was that punctate basophilic erythrocytes were abnormal both in haemoglobin content and physical structure as a consequence of damage by lead before the corpuscles were released from the haemopoietic site. The peripheral action of lead has not been evaluated with certainty. Aub, Fairhall, Minot, and Reznikoff (1926) made extensive studies in vitro, mainly on washed red blood cells in phosphate-free Ringer solutions. The addition of small quantities of lead chloride caused increased mechanical fragility of the corpuscles which, however, became more resistant to hypotonic haemolysis. An increased mechanical fragility of the circulating corpuscles through contact with plasma lead was regarded as the essential feature of the anaemia of lead poisoning. Indirect evidence which supported this view has been reported more recently, namely, raised urobilinogen excretion in lead-poisoned guinea-pigs (Baikie, 1954) and coproporphyrinuria I in severely poisoned workmen (Kench, Lane, and Varley, 1952). The data in a recent investigation (Holecek and Penickova', 1957) are unfortunately qualitative only. Aub and his colleagues postulated that blood lead was distributed between plasma inorganic phosphate and phosphate groups on the red blood corpuscular surface, now known to be largely dominated by such groups (Furchgott and Ponder, 1941). Lead in whole blood caused much less damage to the erythrocytes than in phosphate-free Ringer suspensions owing to the protection afforded by the plasma inorganic phosphate. Small quantities of lead added to whole blood remain in the plasma as colloidal lead phosphate, but with larger quantities relatively more lead would become bound to the erythrocytes. Changes in fragility were ascribed to the release of hydrochloric acid in the corpuscular surface layers by interaction of lead salt with inorganic phosphate groups. Certain aspects of this hypothesis have been discounted. Bischoff, Maxwell, Evans, and Nuzum (1928) observed that lead salts of weak acids, e.g., lead glycerophosphate, were equally productive of similar changes in the red blood cell although no mineral acid was released. Bambach, Kehoe, and Logan (1942) and Mortensen and Kellogg (1944) described a rapid removal of lead by the red cells even at low blood levels. Clarkson and Kench (1958) from kinetic studies of interaction of lead with human erythrocytes in vitro, have envisaged a process involving coagulation and flocculation of a peptized lead phosphate sol on the cellular membrane. No competitive inhibition of uptake of lead was observed with any of a number of potential competitors tested, including other metal ions, namely, Cu2+, Hg2+, (uO2)2+, and Tl4+. Chelating agents such as EDTA removed lead attached to erythrocytes only slowly in vitro, indicating that the metal was present in a practically unionized state. The present investigation was undertaken to reexamine the behaviour of human erythrocytes following exposure to lead in vitro, in the light of *Present address: Department of Biochemistry, Rochester University, New York.