Potential Erythropoiesis in the Primo-Vascular System in Heart Failure

The primo-vascular system (PVS), composed of primo-nodes (PNs) and primo-vessels (PVs), has been identified in various animal models. However, little is known about its function. Here, we investigated the changes in gross morphology and cellular composition of the organ-surface PVS (osPVS) in rats with heart failure (HF) induced by myocardial infarction. The size of the PNs in rats with HF was larger than in sham rats (1.87 vs. 0.80 mm²; P < 0.01) and the density of osPVS per rat was greater for the HF rats (28 of 6 rats vs. 19 of 9 rats; P < 0.01). In addition, the osPVS number containing red chromophore was greater in HF rats (P < 0.001). The chromophore was identified as hemoglobin. Transmission electron microscopy and H&E staining revealed that the osPVS of HF rats (P < 0.001) possessed more red blood cells (RBCs) than that of the sham rats. In particular, immature RBC number increased in the HF rats (90.7 vs. 42.3%; P < 0.001). Altogether, the results showed that the osPVS in HF rats increased in its size, density, and the proportion of immature RBCs in the PNs, which may indicate that the PVS has erythropoietic activity. Our study will help to elucidate the physiological roles of PVS in normal and disease states associated with HF.