High Salt Induces An Endothelial Hdac1-Stimulating Circulating Factor Leading To Disrupted Renal Microvascular Nitric Oxide Signaling.

High salt diet (HS) decreases endothelial nitric oxide (NO) signaling as described in human and rodent studies. We have previously shown that inhibition of HDAC1 restores NO signaling in the afferent arteriole of HS fed rats. It remains unknown, however, how HS initiates endothelial dysfunction and activates HDAC1. We first investigated if HS induced endothelial dysfunction is acutely regulated by a circulating factor. To test this, male Sprague Dawley rats were fed normal salt diet (NS; 0.49% NaCl) or 2 weeks of HS (4.0% NaCl). Afferent arteriole vasoconstrictor responses to the NOS inhibitor, L-NAME, were monitored using the in vitro, blood perfused juxtamedullary nephron preparation. Perfusing arterioles from NS fed rats with HS blood blunted constriction to L-NAME (88 ± 1% of Con) compared to perfusing with NS blood (76 ± 2% of Con; P=0.0003), but not completely as seen in arterioles from HS fed rats perfused with HS blood (96 ± 2% of Con; P=0.0095). HS arterioles perfused with NS blood had similar L-NAME-induced constriction (75 ± 2% of Con) compared to arterioles from NS fed rats perfused with NS blood (P=0.9107). These results suggest HS induces endothelial function through an acute-acting circulating factor. This was not due to increased plasma arginase activity (NS: 7.96 ± 3.73 U/L vs HS: 5.42 ± 1.83 U/L P=0.5813) which competes with NO synthase 3 for arginine, nor was it due to decreased superoxide scavenging capacity of the plasma (NS: 7.96 ± 3.73 U/L vs HS: 5.42 ± 1.83 U/L P=0.5813) as measured by a cytochrome c reduction based assay. We then investigated if HS increased endothelial HDAC1 activity. Renal endothelial cells were isolated via magnetic activated cell sorting from NS and HS fed rats and incubated in plasma from the same rat. HDAC1 activity was monitored as the MS-275 (HDAC1 specific inhibitor) inhibitable portion of total HDAC activity. We found HS significantly increased renal endothelium HDAC1 activity (NS: 0.38 ± 0.03 pmol/min vs HS:0.94 ± 0.19 pmol/min, P=0.01). We conclude that HS disruption of renal microvascular NO signaling is initiated by a circulating factor(s) that is dependent upon increased endothelial HDAC1 activity.