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1 First Department of Physiology, Shinshu University School of Medicine, Matsumoto; 2 Department of Electronics and Control Engineering, Nagano National College of Technology, Nagano, 381-8550; and 3 Institute of Organ Transplants, Reconstructive Medicine, and Tissue Engineering, Shinshu University Graduate School of Medicine, Matsumoto 390-8621, Japan
Parathyroid
hormone-related protein (PTHrP) was originally found as a tumor-derived
vasoactive factor and has also been known to produce significant
relaxation of vascular smooth muscles. Thus effects of PTHrP-(1-34), a
PTH receptor-binding domain, on spontaneous lymphatic pump activity was
investigated in isolated pressurized lymph vessels of mice. Low
concentrations (1 × 10
10 and 3 × 10
10 M) of PTHrP-(1-34) dilated lymph vessels and reduced
the frequency of pump activity, whereas high concentrations (1 × 10
9 to 1 × 10
8 M) of PTHrP-(1-34)
caused dilation with cessation of the lymphatic pump activity.
N
-nitro-L-arginine methyl ester
(L-NAME; 3 × 10
5 M) but not
indomethacin (1 × 10
5 M) significantly reduced the
PTHrP-(1-34)-induced inhibitory responses of the lymphatic pump
activity. In the presence of L-NAME (3 × 10
5 M) and L-arginine (1 × 10
3 M), the L-NAME-induced inhibition in the
PTHrP-(1-34)-mediated responses was significantly reduced.
Glibenclamide (1 × 10
6 M) significantly suppressed
the inhibitory responses of the lymphatic pump activity induced by
PTHrP-(1-34) and
S-nitroso-N-acetyl-penicillamine. The
PTHrP-(1-34)-mediated inhibitory responses were significantly reduced
by treatment with PTHrP-(7-34) (1 × 10
7 M). These results suggest that PTHrP-(1-34) inhibits
spontaneous pump activity of the isolated lymph vessels via PTH
receptors and that production and release of endogenous nitric oxide
and activation of ATP-sensitive K+ channels in the lymph
vessels contribute to the PTHrP-(1-34)-mediated inhibitory responses of
the lymphatic pump activity.
mice; nitric oxide; ATP-sensitive K+ channel
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