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Department of Physiology, New York Medical College, Valhalla, New York 10595
It was shown
previously that the presence of endothelium modulates spontaneous
vasomotion of small lymphatic vessels. In the present study, we aimed
to elucidate the nature of endothelium-derived factors, produced in
basal conditions and in response to agonists, that affect the smooth
muscle tone of lymph microvessels in vitro. Afferent lymph microvessels
were isolated from rat iliac lymph nodes, cannulated with glass
micropipettes, and pressurized (6 cmH2O), and changes in their
diameter were investigated with video microscopy. In resting
conditions, isolated lymph vessels exhibited spontaneous constrictions
and dilations. The maximum and minimum diameters
(Dmax and
Dmin) were
149.8 ± 2.9 and 85.8 ± 3.6 µm, respectively. Acetylcholine
(ACh, 10
7 to
10
5 M) and sodium
nitroprusside (SNP, 10
8 to
10
6 M) temporarily
abolished diameter oscillations, increasing the diameter of lymphatics
dose dependently. For example,
10
5 M ACh and
10
6 M SNP increased the
diameter (Dmax)
by 15.2 ± 2.2 and 25.0 ± 2.7 µm, respectively. Treatment of
vessels with NG-nitro-L-arginine
(10
4 M) significantly
reduced the amplitude of diameter oscillations and nearly completely
eliminated ACh-induced dilation of lymph microvessels, whereas SNP
(10
6 M) elicited a
significantly greater dilation (55.6 ± 7.5 µm). Arachidonic acid
(AA, 10
8 to
10
6 M) constricted (up to
50 µm), whereas prostaglandin E2
(PGE2, 10
9 to
10
7 M) dilated (up to 40 µm), lymphatic vessels. Indomethacin
(10
5 M) increased both
Dmax and
Dmin and
completely inhibited AA-induced constrictions, but did not affect
PGE2-induced dilations of lymph microvessels. AA-induced constrictions of lymphatics were converted into dilations after treatment with SQ-29,548, a selective
PGH2-thromboxane A2
(PGH2-TxA2,
10
6 M) receptor antagonist,
whereas PGE2-induced dilations
were not affected. We conclude that endothelial nitric oxide and
prostaglandins are important modulators of lymphatic vasomotion, hence
pumping activity of lymph microvessels in vivo.
vasomotion; endothelium; prostaglandin E2; prostaglandin H2-thromboxane A2
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