Age-related differences in myocardial hydrogen ion buffering during ischemia

Background: During myocardial ischemia, accumulation of end products from anaerobic glycolysis (hydrogen ions (H+), lactate) can cause cellular injury, consequently affecting organ function. The cells' ability to buffer H+ (buffering capacity (BC)) plays an important role in ischemic tolerance. Age related differences in myocardial lactate and H+ accumulation (one hour of ischemia) as well as differences in BC, myoglobin (Mb) and histidine (His) contents in the left (LV) and right (RV) ventricles were assessed in neonatal compared to adult pigs. The BC of the septum was also compared. Methods and Results: Neonatal RV and LV had lactate accumulations of 43% and 63% and significantly greater H+ (p < 0.004) compared to the adult. In the neonate LV, BC was 17% significantly poorer (p = 0.0001), had 33% lower Mb (p = 0.0002) and 15% lower His content (p = 0.0004) when compared to the adult. In the RV, despite similar BC between the neonate and adult, myoglobin content was 36% (p = 0.0004) lower in the neonate. The neonate septum had a BC that was 11% lower than that of the adult. With maturation, the adult LV had a BC that was 10% greater (p < 0.01) than the RV while the septum mirrored that of the LV. Conclusions: During maturation to adulthood, the BC of the septum begins to closely resemble the LV. Neonatal hearts have a potentially greater vulnerability to acid-base disturbances during ischemia in both ventricles when compared to hearts of adults. This is due to lower levels of myoglobin and histidine in the young, which could render them more susceptible to injury during ischemia. Condensed Abstract During myocardial ischemia, H+ and lactate accumulation may pose deleterious effects on the heart. The ability to buffer H+ (buffering capacity, BC) affects ischemic tolerance. Although lactate accumulation during 1 h of global ischemia was similar between ventricles of neonatal and adult swine, H+ accumulation was greater and BC, Mb and His content were lower. With maturation, LV BC was higher than the RV while septum developmentally resembled the LV. Thus, hearts of neonates may be at a greater risk of ischemic injury compared to hearts of adults.