| |
Isolated rat thoracic
aorta which is pharmacologically precontracted by phenylephrine
induces photorelaxation when exposed to long wave length UV-light.
The aim of the present study was to characterize the mechanism of
UV-light induced by photorelaxation in the rat aorta. 1. UV light
relaxed both endothelium-intact and -denuded rat aortic rings contracted
by phenylephrine. The magnitude of relaxation on UV light was dependent
on the exposure time and slightly greatly in endothelium-denuded
rings than in endothelium-intact preparations. 2. L-NAME (10 nM-100
uM) but not D-NAME completely inhibited the photorelaxation in a
concentration dependent manner. 3. The UV-induced relaxation was
inhibited by methylene blue (1 -100 uM), and verapamil (100 nM),
and removal of extracellular Ca2+. In contrast, UV-light induced
photorelaxation was potentiated by N(w)-nitro-Larginine (L-NOARG)
treatment. 4. In immunocytochemical analysis of UV-light induced
iNOS and eNOS expression in rat aortas, at which expression levels
were increased in a time-dependent manner on UV-irradiation in aortic
endothelium and smooth muscle, respectively. These results suggest
that UV light-induced photorelaxation may be due to nitric oxide
from exogenously administered L-arginine as well as endogenous nitric
oxide donors such as amino acid and arginine derivatives. Additional
suggestion is that UV light stimulates the expression of nitric
oxide synthases, and its activity for nitric oxide generation is
dependent on cytosolic Ca2+ originated from extracellular space. |
