A high salt diet alters pressure-induced mechanical activity of the rat lymphatics with enhancement of myogenic characteristics.

Abstract

The lymphatic system has become a new player for pathogenesis in salt-sensitive hypertension animals. A high salt diet (HSD) evokes accumulation of Na(+) in the skin of rodents. In response to increase in Na(+)-proteoglycan complex, infiltrated macrophages stimulate secretion of vascular endothelial growth factor (VEGF)-C. Macrophage-derived VEGF-C increases density of the dermal lymph capillaries, indicating that lymphangiogenesis is advantageous to hypertensive animals by buffering elevated blood pressure. However, the effects of a high salt diet (HSD) on changes in mechanical activity of collecting lymph vessels, which directly connect with lymph capillaries, have not yet been determined. Changes in mechanical activity of isolated collecting lymphatics in normal salt diet (NSD) and HSD rats in response to increase in intraluminal pressures were measured by video-microscopy. HSD vessels had smaller % active diameters (maximum and minimum) and higher amplitude compared with NSD vessels. The frequency of lymphatic oscillation was better maintained in HSD rats than in NSD. Lymphatic pump efficiency including stroke volume index (SVI), frequency times SVI, and amplitude times frequency in HSD rats were significantly higher than those of NSD. Thus, a HSD enhances the resistance to pressure-induced decreases in lymphatic pump efficiency. The present ex vivo study suggest that collecting lymphatics of rats enhance myogenic activity and lymphatic pump efficiency to compensate for increase in lymph flow and/or pressure after 2 weeks salt loading.