PARATHYROIDECTOMY DOES NOT AFFECT MESSENGER-RNA OF PTH-PTHRP RECEPTORIN KIDNEY, LIVER, AND HEART

Elevated blood levels of cytosolic calcium - [Ca2+](i) - appear to med iate the downregulation of the mRNA of the PTH-PTHrP receptor in state s with chronic elevation of blood levels of parathyroid hormone (PTH). Data on the effect of hypoparathyroidism on basal levels of [Ca2+]i( )are not available, while those on the mRNA of the PTH-PTHrP receptor are variable. The present study was performed to measure [Ca2+](i) in renal cells, to estimate the concentrations of mRNA of the PTH-PTHrP r eceptor in kidney, liver, and heart, and to examine the phosphaturic r esponse to PTH and adenine 3',5'-cyclic monophosphate (cAMP) in normal rats as well as in animals after 3 weeks of parathyroidectomy (PTX). The basal levels of [Ca2+](i) of the renal proximal tubular cells in P TX animals (163 +/- 5.1 nM) were not different from those in normal ra ts (160 +/- 4.9 nM). The concentrations of the mRNAs of the PTH-PTHrP receptor in kidney, liver, and heart were not upregulated after PTX. T he phosphaturic responses to PTH or cAMP in normal and PTX rats were n ot different. The results show that PTX of rats with the consequent de crease in their blood levels of PTH is not associated with changes in the basal levels of [Ca2+](i), the concentrations of the mRNA of the P TH-PTHrP receptor, and in the phosphaturic response to PTH. These data lend support to the notion that the regulation of the mRNA of the PTH -PTHrP receptor in the presence of excess PTH or its lack is mediated through changes in basal levels of [Ca2+](i).