Effect of anemia on cardiac function, microvascular structure, and capillary hematocrit in rat hearts

The effect of anemia on the coronary microcirculation was studied in young male rats. Chronic anemia resulted in increased left ventricular end-diasto lic pressure and decreased functional reserve. Cardiac mass in anemic anima ls increased by 25%. Capillary and arteriolar densities in these hearts rem ained unchanged, indicating angiogenesis in this experimental situation (es timated aggregate capillary length in the left ventricle of anemic hearts w as 3.06 km compared with 2.35 km in control hearts). Capillary hematocrit w as decreased in chronic anemia less than systemic hematocrit: from 25 to 18 % in anemia versus 45 to 28% in controls. Capillary hematocrit and red bloo d cell spacing were also studied after acute blood withdrawal. Here, capill ary hematocrit was preserved even more: 22 versus 24% in systemic hematocri t. Finally, the same was studied in isolated hearts perfused with solutions of various hematocrits. After perfusion with low-hematocrit solution (14%) , the capillary hematocrit (24%) was even higher than the perfusate hematoc rit! In conclusion, we found evidence of angiogenesis in cardiomegaly induc ed by chronic anemia. Microvascular growth was accompanied by advantageous regulation of red blood cell spacing within these vessels. This was even mo re pronounced during acute hemodilution and in isolated perfused hearts.