[Recent knowledge about the significance of 1,25-hydroxyvitamin D and the development of genetically-induced rickets].

Receptors for the binding of 1,25-hydroxyvitamin D are present in many cell types and are of importance for the regulation of the transcription and function. The 1,25-hydroxyvitamin-D-receptor complexes are in the cells under physiological conditions mainly in the nucleus. The 1,25-hydroxyvitamin D already in a very low concentration in the bone cells further the replication of the DNA and the division of the cells, in the lactotrophic cells of the anterior pituitary the secretion of prolactin, in the B-cells the secretion of insulin and in the epidermis the formation of keratin. In the parathyroid gland it restricts the formation of preproparathormone and in the cultures of lymphocytes the division of cells evoked by the addition of mitogens. The multiplication of various forms of tumour cells and their metastatic spread is inhibited by the administration of 1,25-hydroxyvitamin D3. The equipment with receptors for the 1,25-hydroxyvitamin D is regulated. Biochemical aspects of the development of the 3 different forms of genetically conditioned rachitis are shown.