Contents of sphingolipids (ceramide, sphingomyelin, gangliosides) and the c
omposition of their sphingoid bases were studied in the transplantable rat
nephroma-RA and in rat kidneys. The content of sphingomyelin was about 1.3-
fold decreased and the content of ceramide was about 1.4-fold increased in
the nephroma compared to normal kidneys, and this correlated with a 1.4-fol
d increased activity of neutral sphingomyelinase; however, the activity of
the acidic isoform of the enzyme was virtually unchanged. The content of ga
ngliosides was also increased in the nephroma. Ceramide and sphingomyelin o
f the nephroma, in addition to sphingosine, contained a significant amount
of sphinganine, although a considerable amount of the latter was also found
in the renal ceramide. The ratio sphingosine/sphinganine in sphingomyelins
changed from 65:1 in kidneys to 5:1 in the nephroma. Thus, the biosynthesi
s of sphingoid bases seems to be disturbed in the transplantable rat nephro
ma-RA compared to normal kidneys.