Two selective rat adrenomedullin (AM)-receptor antagonists: AM20-50 and AM24-50.
Adrenomedullin (AM) is a hypotensive peptide, which is produced in several organs and tissues, the functions of which it regulates in a autocrine-paracrine manner. Rat (r) and human (h) AM are 50- and 52-amino acid peptides, which differ for 2-amino acid deletions and six substitutions and contain a disulfide bridge-formed six-membered ring between adjacent cysteine residues in the 14 and 19 and 16 and 21 positions, respectively. The amidated C-terminal sequence is needed for AM to bind its receptors, and the ring structure (but not t he N-terminal sequence) seems to be required for AM to activate its receptors. Hence, we examined the effectiveness of some N-terminus and ring-lackingAM fragments as AM-receptor antagonists in the rat zona glomerulosa (ZG), whose cells are provided with abundant AM binding sites and display an AM-induced inhibition of K+-stimulated aldosterone secretion. Quantitative autoradiographic studies showed that cold rAMI-50, rAM20-50 and rAM24-50 displaced [125I]AM1-50 binding from rat ZG with the same potency and efficacy, which were significantly higher than those of hAM1-52, hAM22-52 and hAM26-52. Accordingly, rAM20-50 and rAM24-50 reversed the inhibitory effect of 10(-8) M rAMI-50 on aldosterone response of dispersed rat ZG cells to 10(-2) M K+ with significantly higher potency and efficacy than hAM22-52 and hAM26-52. Taken together, our findings confirm that CONH2-terminal AM fragments, lacking the six-membered ring structure, act as antagonists of AM receptors in the rat ZG. Moreover, they provide the first evidence that rAMI-50 and its fragments should be used in the investigations carried out in the rat.
Belloni
A S
AS
Department of Human Anatomy and Physiology, Section of Anatomy, University of Padua, Via Gabelli 65, I-35121 Padua, Italy.
Guidolin
D
D
Spinazzi
R
R
Nussdorfer
G G
GG
D053607:Adrenomedullin; D000818:Animals; D008297:Male; D010446:Peptide Fragments; D010455:Peptides / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D058265:Receptors, Adrenomedullin; D043562:Receptors, G-Protein-Coupled / Q000037:antagonists & inhibitors*; D015384:Zona Glomerulosa / Q000378:metabolism
D010446:Peptide Fragments; D010455:Peptides; D058265:Receptors, Adrenomedullin; D043562:Receptors, G-Protein-Coupled; C490339:adrenomedullin (20-50), rat; C490340:adrenomedullin (24-50), rat; C081830:adrenomedullin receptor, rat; D053607:Adrenomedullin