Genetic removal of basal nitric oxide enhances contractile activity in isolated murine collecting lymphatic vessels
JP Scallan, MJ Davis - The Journal of physiology, 2013 - Wiley Online Library
JP Scallan, MJ Davis
The Journal of physiology, 2013•Wiley Online LibraryKey points• Stimulation of nitric oxide (NO) production by lymphatic endothelium was
originally thought to inhibit lymphatic contractile function.• However, recent studies have
suggested that basal NO paradoxically increases the strength of contractions as a
consequence of decreasing contraction frequency.• Here, we tested that hypothesis directly
for the first time by establishing a new preparation where lymphatic vessels were isolated
from transgenic mice and retained robust contractile activity.• Genetic removal of basal NO …
originally thought to inhibit lymphatic contractile function.• However, recent studies have
suggested that basal NO paradoxically increases the strength of contractions as a
consequence of decreasing contraction frequency.• Here, we tested that hypothesis directly
for the first time by establishing a new preparation where lymphatic vessels were isolated
from transgenic mice and retained robust contractile activity.• Genetic removal of basal NO …
Key points
- • Stimulation of nitric oxide (NO) production by lymphatic endothelium was originally thought to inhibit lymphatic contractile function.
- • However, recent studies have suggested that basal NO paradoxically increases the strength of contractions as a consequence of decreasing contraction frequency.
- • Here, we tested that hypothesis directly for the first time by establishing a new preparation where lymphatic vessels were isolated from transgenic mice and retained robust contractile activity.
- • Genetic removal of basal NO using endothelial NO synthase−/− mice led to an increase in contraction strength without increasing contraction frequency, opposing this hypothesis. In contrast, higher levels of NO production stimulated by ACh inhibited lymphatic contractile function in wild‐type and inducible NO synthase−/− mice, consistent with previous studies.
- • Our results show that NO functions in the peripheral lymphatic vasculature to depress contractile function, which will ultimately depress lymph flow that determines fluid homeostasis, humoral immunity and cancer metastasis.
Abstract The role of nitric oxide (NO) in regulating lymphatic contractile function and, consequently, lymph flow has been the subject of intense study. Despite this, the precise effects of NO on lymphatic contractile activity remain unclear. Recent hypotheses posit that basal levels of endogenous NO increase lymphatic contraction strength as a consequence of lowering frequency (i.e. positive lusitropy), whereas higher agonist‐evoked concentrations of NO exert purely inhibitory effects on contractile function. We tested both hypotheses directly by isolating and cannulating collecting lymphatic vessels from genetically modified mice for ex vivo study. The effects of basal NO and agonist‐evoked NO were evaluated, respectively, by exposing wild‐type (WT), endothelial NO synthase (eNOS)−/− and inducible NO synthase (iNOS)−/− lymphatic vessels to controlled pressure steps followed by ACh doses. To compare with pharmacological inhibition of eNOS, we repeated both tests in the presence of l‐NAME. Surprisingly, genetic removal of basal NO enhanced contraction amplitude significantly without increasing contraction frequency. Higher levels of NO production stimulated by ACh evoked dilation, decreased tone, slowed contraction frequency and reduced fractional pump flow. We conclude that basal NO specifically depresses contraction amplitude, and that greater NO production then inhibits all other aspects of contractile function. Further, this work demonstrates definitively that mouse collecting lymphatic vessels exhibit autonomous, large‐amplitude contractions that respond to pressure similarly to collecting lymphatics of other mammalian species. At least in the peripheral lymphatic vasculature, NO production depresses contractile function, which influences lymph flow needed for fluid regulation, humoral immunity and cancer metastasis.
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