Renal Receptors for Parathyroid Hormone in Normal, Parathyroidectomized and Vitamin D-Deficient Rats

We characterized the binding of 125I-[Nle8, Nle18, Tyr34]parathyroid hormone-(1-34) amide [125I-nlPTH-(1-34)] to renal plasma membranes prepared from chicks to determine the effects of secondary hyperparathyroid states on renal PTH receptors. This radioligand exhibited specific binding to membranes with high affinity (Kd, 2-3 X 10(-9) M). Agonists or competitive antagonists of PTH were effective in competing for binding sites labeled with 125I-nlPTH-(1-34), whereas an inactive fragment of PTH, salmon calcitonin, and bovine growth hormone did not compete with the radioligand for renal PTH receptors. Newly hatched chicks raised on control diet with adequate vitamin D and calcium or diets deficient in either vitamin D or calcium were used to study the regulation of renal PTH receptors in experimental models of secondary hyperparathyroidism. We found that both experimental diets resulted in marked hypocalcemia and progressive loss of renal cyclic AMP responsiveness to PTH in vitro. Associated with this refractoriness to the hormone was a marked reduction in PTH receptors in membranes from both vitamin D-deficient and calcium-deficient chick kidney. No change in the affinity of the PTH receptors was found. Vitamin D3, in a single dose of 250 micrograms, partially restored serum calcium of vitamin D-deficient birds toward normal by 72 h and also partly restored renal cyclic AMP responsiveness to PTH and the PTH receptor number toward control values. We conclude that renal refractoriness to PTH observed in experimentally hyperparathyroid animals models is due to a marked loss of plasma membrane receptor sites for PTH without an apparent change in the affinity of the receptors for the hormone.

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Binding of Radioiodinated Bovine Parathyroid Hormone-(1–84) to Canine Renal Cortical Membranes*

Rizzoli¹,

Murray²,

Marx³

et al. 1983

Endocrinology

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Binding of PTH to purified canine renal cortical membranes was investigated using biologically active radioiodinated bovine PTH-(1-84) [bPTH-(1-84)] as radioligand. PTH-(1-84) is thought to be the major circulating form of bioactive PTH, but oxidative inactivation upon iodination has prevented its use as a radioligand probe of PTH receptors. We have labeled PTH-(1-84) by a microelectrolytic constant current method to a high specific activity (180-220 muCi/micrograms), corresponding to an average ratio of 1 mol 125I/mol peptide. Affinity purification on chick renal membranes consistently improved the radioligand-binding properties, with a 6-fold increase in fraction specifically bound. Analysis of equilibrium (180 min at 15 C) competition curves showed two classes of binding sites for bPTH-(1-84). A high affinity binding site appeared to be coupled to activation of adenylate cyclase and exhibited affinity varying between 1.9 and 4.3 X 10(8) M-1. The affinity of this site for bPTH was decreased more than 50% by the nonhydrolyzable analog of GTP, guanyl-5'-yl-imidodiphosphate. A low affinity binding site also was detected (Ka = 0.6-6.2 X 10(6) M-1), and its affinity for bPTH was modulated by the concentration of magnesium. The high affinity sites exhibited hormonal specificity and guanine nucleotide dependency characteristic of peptide hormone receptors, while the low affinity sites did not. Analysis by polyacrylamide gel electrophoresis or high pressure liquid chromatography of the radioligand incubated with or released from purified canine renal cortical membranes revealed a single peak of radioactivity that comigrated with [125I]iodo-bPTH-(1-84). It appears from these studies that cleavage of amino-terminal to residue 43 ([125I]tyrosine) was not required for binding or release of hormone. These experiments indicate that radioiodinated bPTH-(1-84) is a useful probe for further characterization of PTH receptors in kidney and other organs.

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Renal Receptors for Parathyroid Hormone in Normal, Parathyroidectomized and Vitamin D-Deficient Rats

Cited by 3 publications

References 17 publications

Mineral Metabolism in Health and Disease

Mineral Metabolism in Health and Disease

Renal parathyroid hormone receptors in the chick: downregulation in secondary hyperparathyroid animal models

Binding of Radioiodinated Bovine Parathyroid Hormone-(1–84) to Canine Renal Cortical Membranes*

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