Publication: Pathophysiology of primary hyperparathyroidism
Authors
Hellman, P. ; Carling, T. ; Rask, L. ; Akerstrom, G.
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Publisher
Murcia : F. Hernández
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DOI
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info:eu-repo/semantics/article
Description
Abstract
Parathyroid gland is the overall regulatory
organ within the systemic calcium homeostasis. Through
cell surface bound calcium-sensing receptors external
calcium inversely regulates release of parathyroid
hormone (PTH). This mechanism, which is voltage
independent and most sensitive around physiologic
calcium concentrations, is regulated through a 120 kDa
calcium sensing receptor, CaR. Inherited inactivation of
this receptor is the cause for familial hypocalciuric
hypercalcemia (FHH). Parallel research identified the
550 kDa glycoprotein megalin, which also is expressed
on the parathyroid cell surface, as another potential
calcium sensing protein. Although this protein expresses
numerous calcium binding sites on its external domain,
its main function may be calcium sensitive binding and
uptake of steroid hormones, such as 25-OH-vitamin Dg
(bound to vitamin D binding protein) and retinol. In
hyperparathyroidism (HPT), excessive PTH is secreted
and the calcium sensitivity of the cells reduced, i.e. the
set-point, defined as the external calcium concentration
at which half-maximal inhibition of PTH release occurs,
shifted to the right. Pathological cells have reduced
expression of both CaR and megalin, and reduced
amount of intracellular lipids, possibly including stored
steroid hormones. A number of possible genetic
disturbances have been identified, indicating multifactorial
reasons for the disease. In postmenopausal
women, however, the individual group with highest
incidence of disease, a causal relation to reduced effect
of vitamin D is possible. An incipient renal insufficiency
with age, lack of sunshine in the Northern Hemisphere,
and an association to the baT haplotype of the vitamin D
receptor supports this theory. This review summarizes
data on regulation of PTH release, dysregulation in HM;
as well as proliferation of parathyroid cells.
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