Abstract
Objective: To evaluate the age-related changes in active pumping in thoracic duct (TD) from 24-month-old Fisher-344 rats comparing with TD pumping in 9-month rats.
Methods: Lymphatic diameters, contraction amplitude and frequency, ejection fraction, and fractional pump flow were determined in isolated TD preparations. Western blot analyses were performed to evaluate relative levels of eNOS and iNOS in 9- and 24-month-old TD.
Results: Stretch-dependent regulation was altered in aged TD especially at higher levels of pressure: the negative inotropy, negative chronotropy and diminished minute pumping (2- to 3-fold decrease) were observed. Physiological NO/imposed-flow-dependent inhibition was completely abolished in aged TD, yet NO-synthase blockade by l-NAME (10− 4 M) increased pumping in a flow-independent manner. Western blot analyses indicated that the relative levels of eNOS were decreased ∼ 7-fold in the 24-month-old TD when compared with 9-month-old TD; whereas iNOS levels were increased ∼ 10-fold in 24-month-old TD.
Conclusions: These data provide the first evidence that stretch- and imposed-flow-dependent regulatory mechanisms are greatly altered in aged TD. These alterations of active pumping mechanisms in TD appear to be related with age-related disturbances in NO-dependent regulatory pathways, and may reflect diminished lymphatic muscle contractility as well as altered lymphatic endothelium function.
This work was supported by TAMU CERH Grant 5 P30 ES09106-08 and National Institutes of Health Grants HL-070308, HL-075199, and HL-080526. Michael Davis and David Zawieja are greatly acknowledged for the use of diameter analysis program; and for shared resources and valuable advice, respectively. The authors thank Elizabeth Wink, Aleksey Gashev, and Sheng (Max) Yu for their help in primary data analysis.