ETUDE COMPARATIVE DU CONTENU EN RECEPTEURS DE LA 1,25-DIHYDROXYVITAMINE D3 DANS DES MUQUEUSES ET DES ADENOCARCINOMES DIGESTIFS

We have studied and compared the 1,25-dihydroxyvitamin D3 receptor (RD3) content of 154 human digestive carcinoma with the normal mucosa one, removed at distance from the same surgical specimen. The distribution of biopsies is as follows: 5 oesophagus, 10 stomach, 6 small bowel, 35 right colon, 47 left colon, 40 rectum and 11 pancreas. RD3 were measured by the Dextran Coated Charcoal method and characterized by sucrose gradient ultracentrifugation. One single class of high affinity binding sites (kD = 1.5 ± 0.7 x 10-10 M) was defined, with a sedimentation coefficient of approximately 3.4 S. The RD3 was present in the 6 samples of small bowel and in 82% of whole normal mucosa, whatever their localization along the digestive tract and pancreas, while in the tumoral tissue, the RD3 was positive in only 32% of the cases. In these tumor specimens the incidence decreases from 64% in the right colon to 27% in the left colon and only 15% in the rectum (P < 0.001). RD3 rates vary slightly with the localization and are of the same level in normal tissues and in tumors: 10-314 (median = 59) vs 13-175 (median = 64) (P > 0.005) respectively. No significant variations relating to age or sex of patients were found. However, all RD3 positive tumors from left colon and rectum were well differentiated histologically. These results show that the normal colonic mucosa is a potential target for 1,25-dihydroxyvitamin D3, which can play a role in the metabolism of calcium and other ions. They also suggest that vitamin D3 could be a modulator of colorectal cell growth and differentiation and its receptor is frequently lost during malignant transformation.