Br. J. Nutr. zyxwvutsrqp (I979), 42, zyxwvut zx 21 Pathogenesis of oedema in protein-energy malnutrition zy : the significance of plasma colloid osmotic pressure zy BY MARTA FIOROTTO AND W. A. COWARD and zyxwvuts Medical Research Council, zyxwv Milton Road, Cambridge CB4 I XJ MRC Dunn Nutrition Unit, Dunn Nutritional Laboratory, University of Cambridge (Received 16 October 1978 - Accepted zyxw 22 January 1979) I. Rats were made oedematous by feeding them low-protein diets (protein:energy (P:E) 0.005) ad zy /ib., and measurements were made of plasma and interstitial fluid colloid osmotic pressures (n, and ni respectively) and interstitial fluid hydrostatic pressure (Pi) before, and at the onset of, oedema formation. Taken together as (7,- ni+Pi) these forces oppose capillary pressure (P,) and thus determine rates of transcapillary water filtration. Interstitial fluid was sampled, in non-oedematous and oedematous animals, from perforated capsules implanted subcutaneously for the measurement of Pi. Blood, plasma and interstitial fluid volumes were also determined. 2. In Expt I comparisons were made between animals fed on a control diet (P:E 0.210) and the low- protein diet. In normal animals the ratio np:ni was approximately 2, but in protein deficiency it was increased since reductions in the absolute value of ni matched those in np. These changes were observed z weeks after the start of the experiment and became more exaggerated when oedema appeared (weeks I 8-22). 3. Pi was normally negative with respect to atmospheric pressure but increased to values close to zero when oedema formation occurred. zyxwvu 4. Despite the reductions in np that were seen in the protein-deficient animals the sum of the forces oppos- ing filtration (n,- ni+ Pi) did not change significantly during the experiment. 5. Plasma and interstitial fluid volumes expressed per kg body-weight (measured using 1251-albumin and srS042-) were unchanged as n, initially decreased in the protein-deficient animals but increased markedly with the onset of oedema. 6. In Expt 2 comparisons were made between animals fed the low-protein diet adlib. and others fed on the control diet in restricted amounts so that weight loss was the same in the two groups of animals. 7. The wasting induced by restriction of the control diet did not produce reductions in n, or ni and values for Pi were normal. Changes in the animals fed on the low-protein diet were similar to those observed in Expt I. By using 51Cr-labelled erythrocytes it was shown that the expansion in plasma volume that occurred when oedema appeared in the protein-deficient animals was mainly due to a reduction in total erythrocyte volume. Blood volume did not increase significantly. 8. It was concluded that in the hypoproteinaemia induced in the experimental animals reductions in the value of n,, which might otherwise result in an imbalance of forces that would produce excessive rates of transcapillary water filtration, were compensated for by reductions in ni. Increases in Pi also compensated but were quantitatively less important. 9. The significance of the results is discussed in terms of the pathogenesis of oedema in kwashiorkor and the concept of an oncotic threshold for oedema formation in hypoproteinaemia. Oedema in kwashiorkor specifically distinguishes this disease from other forms of protein- energy malnutrition (Lancet, 1970) but there is no general agreement as to its cause. The early discovery that plasma protein concentrations were low, and that albumin :globulin ratios were reduced, in children with kwashiorkor (findings of Harvey, and of Cofiiio Ubico & KlCe, cited by Trowell et al. 1954~) was recognized by contemporary workers as being significant so that Trowell et al. (19546) were able to state that ‘the low level of serum albumin found in children in the acute stage of kwashiorkor plays a considerable part in the production of oedema’. It was presumably thought that oedema formation could be explained in terms of Starling’s hypothesis of transcapillary fluid dynamics (Starling, I 896) which is now usually written as: J = Kt ( (P, - g”9) - (P‘ - m), 0007-1145/’p/3236-2201 $01.00 @ 1979 The Nutrition Society Downloaded from https://www.cambridge.org/core. IP address: 54.163.42.124, on 07 Jun 2020 at 07:17:11, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1079/BJN19790086