CA2-RNA AND PROTEIN INCREASE IN THE RAT PARATHYROID-GLAND WITH ADVANCING AGE( RECEPTOR MESSENGER)

Parathyroid hormone (PTH) release is regulated by extracellular calciu m through a Ca2+ receptor (CaR) located on the surface of the parathyr oid cell. With advancing age, the serum concentration of PTH increases , and evidence suggests that the calcium set-point for PTH release may also increase. To determine whether these changes are linked to a cha nge in CaR expression, we quantitated mRNA and protein for the recepto r in parathyroid glands of 6-week-, 6-month- and 24-month-old rats. Th yroid and kidney tissue were also studied. Between 6 weeks and 24 mont hs of age, CaR mRNA in the parathyroid gland increased 11.4- and 3.3-f old as measured by competitive reverse transcription PCR and solution hybridization assays respectively. Message levels for the receptor als o increased in the thyroid but not in the kidney. Coincident with the increase in message levels, receptor protein concentration in the para thyroid increased 7-fold between 6 weeks and 24 months of age. These r esults suggest that the altered relationship between extracellular cal cium and PTH release observed in aging is associated with dramatic cha nges in Call metabolism. That PTH secretion is increased despite incre ased receptor concentration suggests that aging may impair calcium bin ding or coupling between the CaR and down-stream effector elements in the pathway regulating PTH release.