Lysosomal enzyme changes in growing and regressing mammary tumours

Rat mammary tumours induced by 7,12-dimethylbenza]anthracene can undergo repeated growth and regression during successive pregnancies. In a 10-day period after birth about half of the tumours regressed 50% or more. The concentrations of the lysosomal enzymes increased in regressing mammary tumours to the following multiples of the initial values: β-glucuronidase, 7·7; β-galactosidase, 3·9; cathepsin, 2·9; acid ribonuclease, 2·1; arylsulphatase A, 1·5; acid phosphatase, 1·4. In contrast, several non-lysosomal enzymes failed to increase. Activities in the post-partum uterus increased to the following multiples of the initial values: β-glucuronidase, 5·8; cathepsin, 5·5; acid ribonuclease, 4·3; β-galactosidase, 2·2; acid phosphatase, 1·8. Arylsulphatase A in the post-partum uterus decreased significantly, suggesting a non-lysosomal distribution or a special function related to pregnancy. No other significant changes were observed in the lysosomal or non-lysosomal enzymes in the hormone-independent liver or hormone-dependent normal mammary gland. The ratio of free to bound arylsulphatase A and acid ribonuclease decreased slightly 1–3 days after birth because of problems in homogenizing the tumours. At days 4–8, however, there was a dramatic increase in the ratio of the free to bound activities. The results can be explained in terms of the lysosomal theory of intracellular digestion.