Ts. Hakim et al., SEGMENTAL PULMONARY VASCULAR-RESPONSES TO ATP IN RAT LUNGS - ROLE OF NITRIC-OXIDE, Journal of applied physiology, 82(3), 1997, pp. 852-858
ATP exhibits vascular presser and depressor responses in a dose- and t
one-dependent manner. The vascular site of ATP-induced contraction or
dilation has not previously been characterized. Using the vascular occ
lusion technique, we investigated the effects of ATP in isolated rat l
ungs perfused with autologous blood (hematocrit = 20%) and described i
ts action during resting and elevated tone in terms of changes in resi
stances of the small and large arteries and veins. During resting tone
, ATP (10(-5) M) caused contraction primarily in the small arteries an
d, to some extent, in the small veins, suggesting that P-2x purinocept
ors are present in these small vessels. During hypoxia, ATP caused dil
ation primarily in the small arteries, suggesting that P-2y purinocept
ors are predominant in small arteries. During U-46619-induced contract
ion, which occurred evenly throughout the four segments, ATP caused di
lation in the large arteries and veins but not in the small arteries a
nd veins. After treatment with N-omega-nitro-L-arginine to inhibit nit
ric oxide synthesis, ATP-induced contraction was potentiated, and its
dilatory effects during hypoxia were attenuated. The action of ATP was
independent of prostanoids, because its constrictor and dilatory resp
onses were not affected significantly by indomethacin. in conclusion,
the results indicate that the effects of ATP on the pulmonary vasculat
ure are primarily due to P-2x and P-2y purinoceptors in the small arte
ries. Contribution of these purinoceptors in other vessels to changes
in total vascular resistance in rat lung was minor.