Influence of Guanyl Nucleotides on Parathyroid Hormone- Stimulated Adenylyl Cyclase Activity in Renal Cortical Membranes*

Abstract

The interaction of 3 guanyl nucleotides with parathyroid hormone (PTH)-sensitive adenylate cyclase in canine renal cortical membranes was assessed. Results seen after mixing various proportions of the naturally occurring nucleotide GTP, and the nucleotide analogs 5''-guanylylimidodiphosphate (Gpp(NH)p) and 5''-guanylyl methylene diphosphonate (Gpp(CH2)p) suggest that the compounds share a common locus of action, probably distal to the hormone-receptor interaction. The nucleotide (Gpp(NH)p) exerted a marked influence on a variety of synthetic analogs of PTH, increasing the apparent affinity of all PTH derivatives tested and the intrinsic activity of all partial agonists. The potency of the NH2-terminal tetratriacontapeptide of bovine PTH (bPTH), which in assays using dog renal membranes is only 20% that of the native hormone, increased to 100% when assayed with the nucleotide, and the hormone analog (deamino-Ala-1)-bPTH-(1-34), was active in vivo but inert in in vitro adenylyl cyclase assays in the absence of the nucleotide, was a partial agonist in its presence. The analog bPTH-(1-26), previously found to be inert, was a partial agonist in the sensitive canine renal adenylyl cyclase assay even in the absence of added nucleotide, but was virtually a full agonist in the presence of added Gpp(NH)p. Further studies employing the guanyl nucleotide to determine the potential role of GTP in hormone action in vivo and for more effective use of the in vitro adenylate cyclase assay to examine the potency of hormone analogs may be valuable.