Calcium-sensing receptor expression and parathyroid hormone secretion in hyperplastic parathyroid glands from humans.
In uremic patients, severe parathyroid hyperplasia is associated with reduced parathyroid calcium-sensing receptor (CaR) expression. Thus, in these patients, a high serum Ca concentration may be required to inhibit parathyroid hormone (PTH) secretion. This study compares the magnitude of reduction in CaR expression and the degree of the abnormality in Ca-regulated PTH release in vitro. A total of 50 glands from 23 hemodialysis patients with refractory hyperparathyroidism were studied. Tissue slices were incubated in vitro to evaluate (1) the PTH secretory output in a normal Ca concentration (1.25 mM) and (2) the PTH secretory response to high (1.5 mM) and low (0.6 mM) Ca concentration. Tissue aliquots were processed for determination of CaRmRNA expression. The results showed that, corrected for DNA, parathyroid tissue with lowest CaR expression secreted more PTH than that with relatively high CaR expression (146 +/- 23 versus 60 +/- 2 pg/microg DNA; P < 0.01). Furthermore, glands with low CaR expression demonstrated a blunted PTH secretory response to both the inhibitory effect of high Ca and the stimulatory effect of low Ca. The study also showed that the larger the gland, the lower the CaRmRNA expression. Thus, large parathyroid glands produce a large amount of PTH not only as a result of the increased gland size but also because the parathyroid tissue secretory output is increased. These abnormalities in PTH regulation are related to low CaR expression.
Cañadillas
Sagrario
S
Research Unit, Hospital Universitario Reina Sofia, Avd Menendez Pidal s/n, Cordoba 14004, Spain.
Canalejo
Antonio
A
Santamaría
Rafael
R
Rodríguez
Maria E
ME
Estepa
Jose C
JC
Martín-Malo
Alejandro
A
Bravo
Juan
J
Ramos
Blanca
B
Aguilera-Tejero
Escolastico
E
Rodríguez
Mariano
M
Almadén
Yolanda
Y
D005260:Female; D006801:Humans; D006962:Hyperparathyroidism, Secondary / Q000209:etiology / Q000503:physiopathology*; D006965:Hyperplasia; D066298:In Vitro Techniques; D007676:Kidney Failure, Chronic / Q000150:complications / Q000628:therapy; D008297:Male; D010280:Parathyroid Glands / Q000378:metabolism* / Q000473:pathology; D010281:Parathyroid Hormone / Q000096:biosynthesis*; D044169:Receptors, Calcium-Sensing / Q000096:biosynthesis*; D006435:Renal Dialysis; D014511:Uremia / Q000209:etiology / Q000628:therapy
D010281:Parathyroid Hormone; D044169:Receptors, Calcium-Sensing