MATURATIONAL DIFFERENCES IN CORONARY FLOW AND INTERSTITIAL TRANSUDATEADENOSINE DURING ALTERATION OF PERFUSATE OXYGENATION IN ISOLATED RABBIT HEARTS

This study was designed to investigate effects of perfusate oxygenatio n and maturation on coronary flow (CF), interstitial transudate adenos ine (ITA) and coronary effluent adenosine (CEA) in isolated rabbit hea rts. Hearts were paced at a fixed rate and were perfused under constan t pressure at two different levels of perfusate oxygenation: baseline (B) (pO(2)=408+/-7 mmHg, O-2 content = 1.28 +/- 0.03 ml O-2/dl) and a lower level (L) (pO(2)=189+/-4 mmHg, O-2 content=0.59+/-0.02 ml O-2/dl ). CF was higher in immature (I, age 5 weeks) compared with mature (M, age 12 weeks) hearts at both levels of perfusate oxygenation (9.7+/-0 .4 vs. 7.7+/-0.3 and 12.9+/-0.4 vs. 9.2+/-0.3 ml/min/g). I hearts had correspondingly higher values for myocardial oxygen consumption (MVO(2 )) (53+/-3 vs. 49+/-2 and 39+/-3 vs. 35+/-2 mu L O-2/min/g), but simil ar values for venous oxygen tensions (vO(2)) (240+/-9 vs. 219+/-10 and 74+/-4 vs. 62+/-3 mmHg), compared with M hearts at B and L. Although interstitial transudate adenosine (ITA) concentration was similar in I and M hearts at B (409+/-75 vs. 254+/-39 nM), it was lower in I than M hearts at L (2500+/-770 vs. 4210+/-1000 nM). Comparing responses to reduction of perfusate oxygenation, a similar decrement in vO(2) (175/-10 vs. 166+/-12 mmHg) was found to correspond to a lesser increment in ITA (2090+/-110 vs. 3950+/-480), but a greater increment in CF (3.2 +/-0.2 vs. 1.5+/-0.4 ml/min/g) in I than in M hearts. CEA concentratio n was, in general, higher at L than at B, but was similar in I and M h earts for both experimental conditions of perfusate oxygenation. These results suggest that: (1) CF was higher in I than M hearts due to gre ater metabolic demand; (2) CF was equally effective in maintaining myo cardial oxygenation in both groups; (3) adenosine may help mediate hyp oxia-induced coronary vasodilation in isolated hearts from both age gr oups; and (4) the relationships between myocardial oxygenation and int erstitial adenosine concentration as well as between interstitial aden osine concentration and coronary flow are altered as a consequence of maturation in isolated rabbit hearts.