THE SIGNIFICANCE OF ELECTROPHORETIC SERUM PROTEIN CHANGES IN PREGNANCY

SERUM protein changes during pregnancy have been studied by the method of paper strip electrophoresis by Paton, Robertson and Wellby (1954), Brown (1954), and von Studnitz (1955). Since their findings were not in complete agreement a similar study was done in this hospital in 1956 (MacGillivray and Tovey, 1957). It was shown that during the first seven months of pregnancy the serum albumin value fell, and the a, and f l globulin values rose, the rise in the a value being the greater (50 per cent against 30 per cent). From seven months till term these changes were virtually arrested unless toxaemia developed. During early pregnancy the y globulin value showed a slight insignificant rise; this was followed by a steady continuous fall until term. The principle serum protein changes during pregnancy were therefore considered to be a lowering of the albumin fraction and a raising of the a2 globulin fraction. Since the publication of these results one of the authors has extensively studied the general significance of electrophoretic serum protein changes (Tovey, 1959). Such changes can be attributed to altered serum protein metabolism. Serum protein anabolism occurs in the liver and plasma cclls, and catabolism probably in the kidneys. The liver produces albumin, a,, a2 and /3 globulins, plasma cells produce y globulin, whilst the kidneys primarily catabolize proteins of low molecular weight. Alteration in function at any of these three sites affects the appropriate serum protein fractions. Approximately 27 g. of low molecular weight protein pass through into the glomerular filtrate per day (Dock, 1942). This protein is reabsorbed by the renal tubules, being broken down during the process and therefore lost to the body (Spector, 1954; Oliver et al., 1954, 1955; Eliasch, Sellers, Rosenfeld and Marmorston, 1955). In health this selective serum protein loss is replaced exactly; but in certain diseases and physiological states this loss exceeds replacement with the result that the serum albumin level falls and the relative a , value rises. The albumin level falls because the loss of this fraction into the glomerular filtrate is the greatest (M.V., 69,000) : the a, globulin value shows a relative rise because the loss of this fraction into the glomerular filtrate is the least (a, globulin is the serum protein fraction with the most consistent highest molecular weight, 300,000). The principle serum protein changes during pregnancy therefore suggest increased renal protein catabolism. This contention is supported by inulin clearance studies. During the first two trimesters the glomerular filtration rate rises from 125 ml. /minute to approximately 180 ml. /minute (Bucht, 1951; Bucht and Werko, 1953; de Alvarez, 1956); such a rise increases renal protein catabolism by 50 per cent, from 27 to 40 g. per day. During the last months of pregnancy the glomerular filtration rate falls from 180 ml. / minute to 140 ml. /minute. This should reduce the amount of protein lost into the glomerular filtrate from 40 to 30 grams per day and the maternal serum protein pattern should revert towards normal. But in fact no significant change is seen in the maternal protein pattern. It could be that, as the glomerular filtration rate falls, glomerular permeability increases so that the quantity of protein passing through into the glomerular filtrate per day remains unchanged.