Metabolic hyperemia is reduced in adult vs. immature guinea pig hearts.

We have previously shown that maturation is associated with decreased maximum coronary flow (CF) elicited pharmacologically or by transient coronary occlusion (Toma, B.S., R.D. Wangler, D.F. DeWitt, and H.V. Sparks. Circ Res. 57: 538-544, 1985). The present study examines the influence of maturation on CF and adenosine release (RADO) during increased myocardial metabolism. Langendorff-perfused hearts from 1- (immature) and 18- (adult) mo-old guinea pigs were given norepinephrine to increase myocardial oxygen consumption (MVO2). CF, oxygen delivery, and venous oxygen tension were significantly lower in the 18-mo-old group for a given MVO2, before and during norepinephrine infusion. Administration of the selective beta-adrenergic agonist isoproterenol, or infusion of norepinephrine during alpha-adrenergic blockade with phentolamine did not significantly increase CF more than norepinephrine at an equivalent MVO2. RADO, relative to MVO2, was greater in 18-mo-old hearts (vs. 1-mo) during norepinephrine infusion. We conclude that in isolated perfused nonworking hearts 1) myocardial metabolic hyperemia decreases during maturation; 2) the observed flow decrement is not the result of increasing alpha-adrenergic activity during maturation; and 3) the flow decrement results in a reduced oxygen supply-to-demand ratio and an increased RADO.