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Department of Physiology, New York Medical College, Valhalla, New York 10595
Fluid dynamic forces have substantial effects
on the movement of lymph and activity of lymph vessels. The effect of
increases in intraluminal flow on spontaneous pumping activity of
isolated collecting lymphatics has not yet been characterized in a
condition in which the intraluminal pressure is constant. Thus, in
afferent lymph microvessels isolated from rat iliac lymph nodes,
changes in maximum (Dmax) and minimum (Dmin)
diameter to increases in perfusate flow were investigated in the
presence of a constant perfusion pressure of 6 cmH2O.
Intraluminal flow was elicited by increases in the difference between
outflow and inflow pressures (Pdiff, from 0 to 6 cmH2O). Diameters were measured by videomicroscopy. In
response to increases in perfusate flow, Dmax and
Dmin of lymphatics decreased from 157.5 ± 6.1 to 90.9 ± 5.6 µm and from 91.9 ± 5.3 to 66.3 ± 3.6 µm, respectively,
whereas vasomotion frequency increased from 18.0 ± 0.7 min
1 to 23.4 ± 1.1 min
1 (at
Pdiff of 4 cmH2O). Removal of extracellular
Ca2+ abolished spontaneous diameter oscillations; under
these conditions the passive diameter of lymphatics was 216.0 ± 7.1 µm and did not change in response to increases in perfusion. In the
absence of endothelium, flow-induced changes in Dmax,
Dmin, and oscillation frequency were eliminated.
N
-nitro-L-arginine methyl ester,
an inhibitor of nitric oxide synthase, did not affect flow-induced
changes in diameter of lymphatics. In contrast, indomethacin, an
inhibitor of prostaglandin synthesis, or SQ-29,548, a
PGH2/thromboxane A2
(PGH2/TxA2) receptor blocker, inhibited the perfusion-induced reduction of Dmax and
Dmin of lymphatics and also the increase in the frequency
of vasomotion. These findings suggest that the sensitivity of lymphatic
endothelium to increases in intraluminal flow could provide an
important local intrinsic mechanism for the control of lymphatic
resistance by release of constrictor prostanoids
PGH2/TxA2.
intraluminal flow; lymphatic vasomotion; amplitude; frequency; endothelium-derived constrictor factors
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