It is known that hypoxia causes pulmonary artery constriction normally maintaining optimal ventilation-perfusion matching in the lung but leading to pulmonary hypertension development. Although it is known that sustained hypoxic pulmonary vasoconstriction (HPV) is critically dependent on both the endothelium and glycolysis, the signaling pathways remain unclear [1]. The aim of this study was to determine the role of gap junctions in HPV development. The vascular tone was measured on isolated small intrapulmonary arteries (IPA) from male Wistar rats (200-250g) using a wire myograph technique. Animals were killed by pentobarbital injection (80 mg/kg). Values are means ± S.E.M., compared by Student’s t-test for paired data. Hypoxia (PO2 2-3 mm Hg) elicited a biphasic response in tension in IPA. The transient HPV phase I consisted 38.89±3.97% of the contraction elicited with 80 mM K+ (TK) (n=10) and the sustained phase II reached a level of 18.62±1.78% TK (n=10) after 40 min of hypoxia in the vessels preconstricted with prostaglandin F2α (PGF2α, 3 µM). Application of gap junctions inhibitor 18β-glycyrrhetinic acid (18β-GA, 30 µM) abolished HPV phase II (4.2±2.36% TK, n=10, P<0.001) but had not effect on the phase I (37.48±3.49% TK, n=10, P>0.05) in PGF2α-precontracted IPA. In IPA precontrtacted with 25 mM K+ 18β-GA (30 µM) also inhibited HPV phase II (1.86±2.49%, n=7 vs. 12.67±2.32% TK in control, n=7, P<0.05) and had not effect on the phase I (22.06±3.16% TK, n=7 vs. 25.39±2.59% TK in control, n=7, P>0.05). In nonprecontracted IPA 18β-GA (30 µM) led to reduction of the sustained HPV phase (2.92±0.29% TK, n=8 vs. 4.66±0.61% TK in control, n=8, P<0.05) without effect on the transient HPV phase I (3.75±1.15% TK, n=8 vs. 2.24±0.69% TK, in control, n=8, P>0.05). Endothelium removing in IPA resulted in reduction in HPV transient phase amplitude (10.71±1.79% TK, n=8 vs. 38.48±7.01% TK in intact control, n=8, P<0.01) and abolished the sustained HPV (-1.03±2.21% TK, n=8 vs. 15.26±2.22% TK, in intact control, n=8, P<0.001), whereas 30 µM 18β-GA enhanced this effect (-17.27±4.04% TK, n=8 vs. -1.03±2.21% TK in endothelium-denuded control, n=8, P<0.01). 18β-GA had no effect on the phase I (11.28±2.1% TK, n=8, vs. 10.71±1.79% TK in deendothelised control, n=8, P>0.05). Taken together, these data indicates that myoendothelial gap junctions can be involved to HPV development reflecting possibility of a novel pathway existing for signaling during hypoxia in pulmonary artery that supports the sustained phase of HPV.