Cardiac function, microvascular structure, and capillary hematocrit in hearts of polycythemic rats

The effect of polycythemia on the coronary microcirculation was studied in young male rats. Two experimental models of polycythemia were employed: cob alt-induced polycythemia, which mimics hypoxia-induced changes, and erythro poietin-induced polycythemia, which circumvents these changes. In both mode ls, baseline left ventricular function was normal, whereas maximal systolic and developed pressures were decreased. In cobalt-treated rats the left ve ntricular functional reserve was also compromised. Morphometric analysis of the left ventricle confirmed previously described improved geometric condi tions for oxygen supply at the distal portions of capillaries (smaller doma in areas and shorter capillary segments). In cobalt-treated but not in eryt hropoietin-treated rats, increased capillary angiogenesis was also detected . In the hearts from rats with both types of polycythemia, a small but sign ificant increase in the formation of arterioles was found. Capillary linear hematocrit was within the normal range in both types of polycythemia despi te sizeable increases in systemic hematocrit. Significant differences in re d blood cell distribution within capillaries were found between proximal an d distal portions in all experimental groups.