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Rate-sensitive contractile responses of lymphatic vessels to circumferential stretch
Phasic contractile activity in rat portal vein is more sensitive to the rate of change in length than to absolute length and this response is widely assumed to be a general characteristic of myogenic behaviour for vascular smooth muscle. Previously, we found that rat lymphatic vessels exhibit phasic...
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Published in: | The Journal of physiology 2009-01, Vol.587 (1), p.165-182 |
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Main Authors: | , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Phasic contractile activity in rat portal vein is more sensitive to the rate of change in length than to absolute length and
this response is widely assumed to be a general characteristic of myogenic behaviour for vascular smooth muscle. Previously,
we found that rat lymphatic vessels exhibit phasic contractile behaviour similar to that of portal vein. In the present study,
we hypothesized that lymphatic muscle would exhibit rate-sensitive contractile responses to stretch. The hypothesis was tested
on rat mesenteric lymphatics (90â220 μm, i.d.) using servo-controlled wire- and pressure-myograph systems to enable ramp increases
in force or pressure at different rates. Under isometric conditions in wire-myograph preparations, both the amplitude and
the frequency of phasic activity were enhanced at more optimal preloads, but superimposed upon this effect were bursts of
contractions that occurred only during fast preload ramps. In such cases, the ratio of contraction frequency during the ramp
to that at the subsequent plateau (at optimal preload) was > 1. Further, the frequency ratio increased as a function of the
preload ramp speed, consistent with a rate-sensitive mechanism. In contrast, the amplitude ratio was < 1 and declined further
with higher ramp speeds. Downward preload ramps produced corresponding rate-sensitive inhibition of contraction frequency
but not amplitude. Similar findings were obtained in pressurized lymphatics in response to pressure ramps and steps. Our results
suggest that lymphatics are sensitive to the rate of change in preload/pressure in a way that is different from portal vein,
possibly because the pacemaker for generating electrical activity is rate sensitive but lymphatic muscle is not. The behaviour
may be widely present in collecting lymphatic vessels and is probably an important mechanism for rapid adaptation of the lymphatic
pump to local vascular occlusion. |
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ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.2008.162438 |