The myocardial response to adrenomedullin involves increased cAMP generation as well as augmented Akt phosphorylation.
In this work we aimed to observe (1) the changes in adrenomedullin (AM) and its receptor system - calcitonin receptor-like receptor (CRLR) and receptor activity modifying proteins (RAMPs) - in myocardial ischemic injury and (2) the response of injuried myocardia to AM and the phosphorylation of Akt to illustrate the protective mechanism of AM in ischemic myocardia. Male SD rats were subcutaneously injected with isoproterenol (ISO) to induce myocardial ischemia. The mRNA levels of AM, CRLR, RAMP1, RAMP2 and RAMP3 were determined by RT-PCR. Protein levels of Akt, phosphor-Akt, CRLR, RAMP1, RAMP2 and RAMP3 were assayed by Western blot. Results showed that, compared with that of the controls, ISO-treated rats showed lower cardiac function and myocardial injury. The mRNA relative amount of AM, CRLR, RAMP1, RAMP2 and RAMP3 in the myocardia of ISO-treated rats was increased. The elevated mRNA levels of CRLR, RAMP1, RAMP2 and RAMP3 were positively correlated with AM content in injured myocardia. The protein levels of CRLR, RAMP1, RAMP2 and RAMP3 in injured myocardia were increased compared with that of control myocardia. AM-stimulated cAMP generation in myocardia was elevated in the ISO group, and was antagonized by AM(22-52) and CGRP(8-37). Western blot analyses revealed that AM significantly enhanced Akt phosphorylation in injured myocardia, which was blocked by pretreatment with AM(22-52) or CGRP(8-37). Ischemia-injured myocardia hyper-expressed AM and its receptors - CRLR, RAMP1, RAMP2 and RAMP3 - and the response of ischemic myocardia to AM was potentiated, and the level of Akt phosphorylation was also increased, which suggests that changes in cardiac AM/AM receptor might play an important role in the pathogenesis of myocardial ischemic injury.
Pan
Chun Shui
CS
Institute of Cardiovascular Diseases, Peking University First Hospital, Beijing 100034, China. yongfenqi@yahoo.com
Jin
Shao Ju
SJ
Cao
Chang Qi
CQ
Zhao
Jing
J
Zhang
Jing
J
Wang
Xian
X
Tang
Chao Shu
CS
Qi
Yong Fen
YF
D053607:Adrenomedullin / Q000494:pharmacology*; D000818:Animals; D015153:Blotting, Western; D058286:Calcitonin Receptor-Like Protein; D002316:Cardiotonic Agents / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D004195:Disease Models, Animal; D005786:Gene Expression Regulation / Q000187:drug effects; D006321:Heart / Q000187:drug effects*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D007545:Isoproterenol / Q000633:toxicity; D008054:Lipid Peroxides / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D017202:Myocardial Ischemia / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D020097:Natriuretic Peptide, Brain; D009419:Nerve Tissue Proteins / Q000235:genetics; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D058261:Receptor Activity-Modifying Proteins; D018003:Receptors, Calcitonin / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D058286:Calcitonin Receptor-Like Protein; D002316:Cardiotonic Agents; D047908:Intracellular Signaling Peptides and Proteins; D008054:Lipid Peroxides; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; D058261:Receptor Activity-Modifying Proteins; D018003:Receptors, Calcitonin; C095026:brain natriuretic peptide-35, rat; D020097:Natriuretic Peptide, Brain; D053607:Adrenomedullin; D000242:Cyclic AMP; D051057:Proto-Oncogene Proteins c-akt; D007545:Isoproterenol