Metabolism of Serum Albumin in Tumour-Bearing Rats

A LOWERING of the serum albumin level is a common accompaniment of malignant disease in man (Mider, Alling and Morton, 1950) and of the growth of experimental tumours in animals (Hradec, Dusek and Dlouh'a, 1954). The mechanism whereby this hypoalbuminaemia is produced is still obscure. Two factors must be taken into account when trying to explain this phenomenon , namely, the intensity of biosynthesis of serum albumin in cancerous subjects, and the extent of utilization of this protein within the body (Fenninger and Mider, 1954). The liver is the main, if not the only, seat of albumin production as shown by experiments with hepatectomized animals (Madden and Whipple, 1940). A net synthesis of this protein has also been demonstrated in vitro by incubating liver slices in a suitable medium (Peters and Anfinsen, 1950). Although many studies of liver function have been undertaken in cancer patients and some degree of impairment has been shown in a high percentage of them (Tagnon and Trunnell, 1948), there is as yet no answer to the question whether a decline of serum albumin synthesis in livers of cancerous subjects is the real reason for hypoalbuminaemia occurring in blood. Lack of a suitable definition of this hepatic dysfunction makes it difficult to interpret these results (Fenninger and Mider, 1954). Reports from experiments undertaken in tumour-bearing animals show an enlargement of livers and kidneys while other organs undergo a reduction in their size (Babson, 1954) An impairment of hepatic function can scarcely be supposed in these cases. As it can be seen from these facts, no unequivocal evidence exists up to date that hypoalbuminaemia in malignant diseases is due to the lowered ability of the liver tissue to produce albumin. There is good evidence for a demand for an increased supply of protein in cancerous subjects. Tumours increase in size by the formation of new protein molecules, for which an increased quantity of building materials must be available. Since the liver holds a key position in the nitrogen metabolism of the body, the suggestion has been made that the liver hypertrophy in rats bearing transplantable tumours is in response to the tumour's demand for an increased supply of protein (Babson, 1954). It is a well-known fact that tissues are able to utilize plasma proteins for the formation of their own proteins, as was demonstrated in dogs given plasma proteins parenterally as the only source of nitrogen (Terry, …