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DOI: 10.1055/s-0035-1544443
Increased Economy of Cardiac Substrate Use during Maturation of Rats
Cardiac metabolism has been described very flexible with regard to its substrate choice which is required for postischemic recovery. As an omnivore the heart metabolizes fatty acids, glucose, lactate and proteins with fatty acid and glucose as major substrates. The heart may thus adapt to different metabolic situations. During fetal and early postnatal life, the heart consumes preferentially carbohydrates and may produce lactate. Postnatally a switch in substrate metabolism from preferentially glucose to fatty acids has been described. However, substrate oxidation of the heart during maturation has not been assessed.
We aimed to assess cardiac substrate oxidation and cardiac performance ex vivo in young (5 weeks old), adolescent (9 weeks), young adult (13 weeks) and adult (6 month) rats. Animal size and weight as well as organ weights were determined. Cardiac power, substrate oxidation and it's response to insulin was investigated in the isolated working rat heart. ATP production from substrate oxidation was calculated and related to cardiac power (economy of substrate use).
Results: Increase in body weights was faster than growth of the heart, thus heart to body weight ratio declined. Cardiac power increased with age and reached a constant level at 13 weeks (5W - 9W - 13W - 6M: 3,14 ± 0,20 - 7,35 ± 0,60 - 9,44 ± 0,40 - 10,06 ± 0,65 mW;p < 0,001). Glucose and fatty acid oxidation rates did not differ with age as did the glucose to fatty acid oxidation ratio. Relating substrate oxidation to cardiac power however, revealed that the heart at 5 weeks of age used significantly more substrate derived ATP to produce power compared with later stages (6,45 ± 0,39 - 3,92 ± 0,32 - 3,43 ± 0,27 - 3,14 ± 0,25 mmol/min/W; p < 0,001).
Constant substrate oxidation rates with increasing power led to an improvement in cardiac economy during maturation of animals. Myocardial substrate metabolism becomes more economic with age. It is tempting to speculate that this increased economy may be related to decreased ischemic tolerance.