Effect of development on coronary vasodilator reserve in the isolated guinea pig heart.

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Abstract
Morphological studies have demonstrated an age-related decrease in capillary density and capillary surface area in the developing heart. However, the consequences of these changes on myocardial perfusion are not known. We tested the hypothesis that the decreased capillary density is associated with a reduction in coronary blood flow reserve. To test this hypothesis, we studied coronary responses to adenosine and sodium nitroprusside administration, reactive hyperemia, and autoregulatory capacity. We used a Langendorff-perfused heart preparation from guinea pigs of five different age groups (1 week and 1, 2, 12, and 18 months). Data are expressed as mean .+-. SEM. Maximal coronary flows (ml/min per g) in response to adenosine (10-6 to 10-5 M) infusion are: 27 .+-. 1.3, 18.5 .+-. 1.4, 12.2 .+-. 0.4, 10.3 .+-. 0.3, and 10.6 .+-. 0.8 at 1 week, 1, 2, 12, and 18 months, respectively, with the flows at 2 week and 1 month significantly higher than those at 2, 12 and 18 months. There is a similar trend for a decreased maximum coronary perfusion in response to sodium nitroprusside (10-6 to 10-5 M) and following a 45-second occlusion of the coronary inlet flow. Despite the decreased maximal pharmacological and reactive hyperemic flow reserve, autoregulation of flow is not altered with growth. The pressure-flow relationship exhibits autoregulation between 25 and 55 mm Hg perfusion pressure for all but the 1-week age group, which autoregulates within a narrow range of pressures (20-45 mm Hg). Total maximal coronary flow (ml/min) increases during development; this indicates that the growth of vessels continues with development. However, since coronary perfusion, corrected per unit cardiac mass, decreases significantly, we conclude that the vascular growth lags behind that of the parenchyma.