Acute Anemia Induces Erythropoiesis in Rat Organ Surface Primo-Vascular Tissue

The primo-vascular system (PVS) is a newly identified vascular tissue composed of primo-nodes (PNs) and primo-vessels (PVs). Previously, we reported erythropoietic activity in the organ-surface PVS (osPVS) tissue of rats with heart failure. In this study, we further investigated whether acute anemia could induce erythropoiesis in the PVS of rats, based on the hypothesis that erythropoiesis in osPVS tissue is due to anemia accompanying heart failure. Acute anemia was induced by an intraperitoneal injection of phenylhydrazine (PHZ). Circulating red blood cells (RBCs) and hematocrit decreased by 31.6%, whereas reticulocytes and white blood cells increased at day 3 and day 6 after PHZ treatment. All these parameters recovered to control levels at day 10. At days 3 and 6, we observed an increase in the size of the PNs (P < 0.05), the number of the osPVS tissue samples per rat (P < 0.01), and the proportion of osPVS tissue samples with red chromophore (P < 0.001), which was from the RBCs in the PVS tissue. The number of RBCs, estimated from the PN sections stained with hematoxylin and eosin, increased at day 6 in the rats with anemia (P < 0.01). All these anemia-induced changes in the osPVS tissue recovered to the control levels by day 10. Taken together, the results showed that the morphological and cytological changes in the osPVS tissue appear to be related to the erythropoietic activity induced by acute anemia in rats. This study confirmed the previous findings that the osPVS can exert erythropoietic activity in disease states accompanied by anemia, such as heart failure.