Cardioprotective effect of L-glutamate in obese type 2 diabetic Zucker fatty rats.
1. Because diabetic hearts have an increased threshold for cardioprotection by ischaemic preconditioning (IPC), we hypothesized that protection by L-glutamate during reperfusion is restricted in Type 2 diabetic hearts. Previously, we found that L-glutamate-mediated postischaemic cardioprotection mimics IPC. 2. Rat hearts were studied in a Langendorff preparation perfused with Krebs'-Henseleit solution and subjected to 40 min global no-flow ischaemia, followed by 120 min reperfusion. L-Glutamate (0, 15 and 30 mmol/L) was added to the perfusate during reperfusion of hearts from non-diabetic (Wistar-Kyoto) and diabetic (Zucker diabetic fatty (ZDF)) rats, studied at 16 weeks of age. The infarct size (IS)/area-at-risk (AAR) ratio was the primary end-point. Expression of L-glutamate excitatory amino acid transporter (EAAT) 1 (mitochondrial) and EAAT3 (sarcolemmal) was determined by quantitative polymerase chain reaction and immunoblotting. 3. The ISS/AAR ratio did not differ between control hearts from Wistar-Kyoto and ZDF rats (0.52 ± 0.03 and 0.51 ± 0.04, respectively; P = 0.90). L-Glutamate (15 mmol/L) significantly reduced the IS/AAR ratio in non-diabetic hearts, but not in diabetic hearts, compared with their respective controls. The higher concentration of L-glutamate (30 mmol/L) reduced infarct size in diabetic hearts to the same degree as in non-diabetic hearts (IS/AAR 0.35 ± 0.03 (P = 0.002) and 0.34 ± 0.03 (P = 0.004), respectively). The mitochondrial L-glutamate transporter EAAT1 was downregulated in hearts from ZDF rats at both the mRNA and protein levels (P < 0.0005 and P < 0.0001, respectively). However, there was no change in EAAT3 expression at the protein level. Myocardial L-glutamate content was increased by 43% in diabetic hearts (P < 0.0001). 4. Hearts from obese diabetic rats have an elevated threshold for metabolic postischaemic cardioprotection by L-glutamate. These findings may reflect underlying mechanisms of inherent resistance against additional cardioprotection in the diabetic heart.
Povlsen
J A
JA
Department of Cardiology, Aarhus University Hospital, Skejby, DK-8200 Aarhus N, Denmark.
Løfgren
B
B
Rasmussen
L E
LE
Nielsen
J M
JM
Nørregaard
R
R
Kristiansen
S B
SB
Bøtker
H E
HE
Nielsen
T T
TT
D000818:Animals; D015153:Blotting, Western; D002316:Cardiotonic Agents / Q000494:pharmacology*; D048909:Diabetes Complications / Q000209:etiology / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology / Q000517:prevention & control*; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy* / Q000209:etiology / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D027341:Excitatory Amino Acid Transporter 1 / Q000235:genetics / Q000378:metabolism; D050580:Excitatory Amino Acid Transporter 3 / Q000235:genetics / Q000378:metabolism; D018698:Glutamic Acid / Q000494:pharmacology*; D006439:Hemodynamics / Q000187:drug effects; D008297:Male; D008929:Mitochondria, Heart / Q000187:drug effects / Q000378:metabolism; D009203:Myocardial Infarction / Q000209:etiology / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology / Q000517:prevention & control*; D015428:Myocardial Reperfusion Injury / Q000209:etiology / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology / Q000517:prevention & control*; D009206:Myocardium / Q000378:metabolism / Q000473:pathology; D009765:Obesity / Q000150:complications*; D010477:Perfusion; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011921:Rats, Inbred WKY; D011924:Rats, Zucker; D012508:Sarcolemma / Q000187:drug effects / Q000378:metabolism; D013997:Time Factors; D016277:Ventricular Function, Left / Q000187:drug effects
D002316:Cardiotonic Agents; D027341:Excitatory Amino Acid Transporter 1; D050580:Excitatory Amino Acid Transporter 3; D012333:RNA, Messenger; C493398:Slc1a1 protein, rat; C493392:Slc1a3 protein, rat; D018698:Glutamic Acid