pH paradox and neonatal heart.
BACKGROUND
To evaluate the functional status of the Na+/H+ exchanger in the neonatal heart.


METHODS
On the Langendorff system, isolated neonatal rabbit hearts were arrested by using cardioplegia with or without a specific Na+/H+ exchanger blocker, 5-(N,N dimethyl) amiloride (DMA) (20 microM). Ischemic period was 40 minutes at 37 degrees C or 120 minutes at 20 degrees C before 30 minutes of reperfusion at 37 degrees C. When DMA was added to the cardioplegia solution, it was also added to the reperfusate for the first 5 minutes of reperfusion (20 microM).


RESULTS
Postischemic developed pressure was 50.3+/-7.1 mmHg in the DMA group versus 25.9+/-6 mmHg in the control group (p<0.05) at 37 degrees C and 74.8+/-14.6 mmHg in the DMA group versus 60.6+/-11.5 mmHg in the control group (p<0.05) at 20 degrees C. Postischeimic diastolic pressure was 40.4+/-3.3 mmHg in the DMA group versus 28.4+/-7 mmHg in the control group (p<0.05) at 37 degrees C and 9.6+/-3.1 mmHg in the DMA group versus 15+/-3.7 in the control group (p<0.05) at 20 degrees C. Creatine kinase washout was 296+/-97 IU/L in the DMA group versus 1253+/-537 IU/L in the control group (p<0.05) at 37 degrees C and 370+/-156 IU/L in the DMA group versus 524+/-104 IU/L in the control group (p<0.05) at 20 degrees C.


CONCLUSIONS
1) The Na+/H+ exchanger is active in the neonatal heart. 2) The Na+/H+ exchanger plays a key-role in the pathogenesis of reperfusion injury of the neonatal myocardium. 3) This exchanger is sensitive even for low H+ transmembrane gradients and even under hypothermic conditions.
Baron
O
O
Cardiovascular Research Group, 261 C Heritage Medical Research Center, Edmonton, Alberta, Canada.
Saiki
Y
Y
Rebeyka
I M
IM
D000138:Acidosis / Q000209:etiology / Q000378:metabolism; D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D001794:Blood Pressure; D002118:Calcium / Q000378:metabolism; D003971:Diastole; D005260:Female; D006324:Heart Arrest, Induced / Q000379:methods*; D006859:Hydrogen / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008297:Male; D015428:Myocardial Reperfusion Injury / Q000209:etiology / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D011817:Rabbits; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000502:physiology*; D013696:Temperature
D017923:Sodium-Hydrogen Exchangers; C039465:5-dimethylamiloride; D000584:Amiloride; D006859:Hydrogen; D012964:Sodium; D002118:Calcium