Vitamin D and hyperparathyroidism: the Lumleian Lecture 1981.
Vitamin D appears to influence parathyroid function indirectly through its effects on calcium metabolism rather than by a direct action of its metabolites on the parathyroid glands. In states of both secondary and primary hyperparathyroidism, the quantitative production of 1,25-(OH)2D may be determined by the prevailing concentration of serum 25-(OH)D but there appears to be some constraint that limits the formation of 1,25-0(OH)2D when the provision of its precursor exceeds the physiological. From the absence of this constraint in 'type 2 vitamin D dependency' it is inferred that it may operate through 'self-inhibition' of the renal production of 1,25-(OH)2D. It is shown that the level of serum 25-(OH)D may always exert some influence on the production of 1,25-(OH)2D and that this effect is facilitated by hyperparathyroidism. In developing vitamin D deficiency the reactive secondary hyperparathyroidism may thus function as an adaptive mechanism that sustains the level of serum 1,25-(OH)2D in the face of a diminishing serum 25-(OH)D. Failure of this adaptation and the development of a critical deficiency of 1,25-(OH)2D is regarded as the direct cause of defective mineralisation of bone. This concept would explain the absence of osteomalacia in some patients with very low levels of serum 25-(OH)D and the occurrence of defective osseous mineralisation in hypoparathyroidism.
D015652:25-Hydroxyvitamin D 2; D002117:Calcitriol / Q000097:blood / Q000378:metabolism / Q000627:therapeutic use; D004872:Ergocalciferols / Q000031:analogs & derivatives / Q000097:blood; D006801:Humans; D006961:Hyperparathyroidism / Q000209:etiology* / Q000378:metabolism; D006962:Hyperparathyroidism, Secondary / Q000209:etiology* / Q000378:metabolism; D006996:Hypocalcemia / Q000097:blood / Q000188:drug therapy; D010018:Osteomalacia / Q000188:drug therapy / Q000378:metabolism; D010281:Parathyroid Hormone / Q000097:blood; D014807:Vitamin D / Q000378:metabolism; D014808:Vitamin D Deficiency / Q000150:complications*
D004872:Ergocalciferols; D010281:Parathyroid Hormone; D014807:Vitamin D; D015652:25-Hydroxyvitamin D 2; D002117:Calcitriol