Evidence of 1,25-dihydroxyvitamin D synthesis by the rat Walker carcinosarcoma 256.

We tested the existence of 25-hydroxyvitamin D-1 alpha-hydroxylase activity in the Walker carcinosarcoma 256 implanted in rats. This tumour has been shown to induce hypercalcaemia in the host animal. We found this enzyme activity in tumour homogenates, which was in the same range as that in the kidney of tumour-bearing rats. Our results suggest that 1,25-dihydroxyvitamin D synthesized by the Walker tumour might be involved in the mechanism responsible for the hypercalcaemia in the host rat.