Endothelium-dependent relaxation followed by contraction mediated by NK(1) receptors in precontracted rabbit intrapulmonary arteries

Abstract

In the present study, we examined whether substance P (SP) and SP methyl ester (SPME), a selective NK(1) agonist, cause biphasic responses consisting of endothelium-dependent relaxation (EDR) and contraction (EDC) in precontracted rabbit intrapulmonary arteries. In arteries contracted with PGF(2alpha) (2x10(-6) M), SP as well as SPME caused only EDR at low concentration (10(-9) M) and EDR followed by EDC at higher concentrations, indicating the involvement of NK(1) receptors. The SP (10(-8) M)-induced EDR was abolished in arteries moderately contracted by PGF(2alpha) (5x10(-7) M) and the EDC in arteries maximally contracted by PGF(2alpha) (10(-5) M), indicating that EDR and EDC are inversely dependent on preexisting tone. Indomethacin (10(-8) - 10(-6) M), a cyclo-oxygenase inhibitor, and ozagrel (10(-8) - 10(-6) M), a TXA(2) synthetase inhibitor attenuated the EDC in the SPME (10(-7) M)-induced biphasic response and markedly potentiated the EDR. AA-861 (10(-8) - 10(-6) M), a 5-lipoxygenase inhibitor, did not affect the EDR or EDC. L-N(G)-nitro-arginine methyl ester (10(-5) - 10(-4) M), a nitric oxide synthase inhibitor, attenuated the EDR and slightly potentiated the EDC. CP-99994 (10(-10) - 10(-8) M), an NK(1) antagonist, attenuated the EDC and potentiated the EDR in the SPME (10(-7) M)-induced biphasic response, while the NK(2) antagonist SR-48968 (10(-9) - 10(-7) M) had no effect. CP-99994 attenuated the SPME (10(-7) M)-induced EDC under EDR-blockade to a greater extent than the EDR under EDC-blockade, indicating that CP-99994 enhanced the EDR component by preferential inhibition of the EDC component. In conclusion, NK(1) agonists caused a biphasic endothelium-dependent response (EDR and EDC) in submaximally precontracted intrapulmonary arteries. The EDC and EDR mediated by NK(1) receptors may play physiological and/or pathophysiological roles in modulation of vascular tone.

Figure 1

Representative tracings of responses induced by substance P (SP) and substance P methyl ester (SPME) in endothelium-intact rabbit intrapulmonary arteries precontracted with PGF_2α (2×10⁻⁶ M). Figures with dots show concentrations of peptides (−log M).

Figure 2

Endothelium-dependent relaxation (EDR) and contraction (EDC) induced by SP and substance P methyl ester (SPME) in endothelium-intact rabbit intrapulmonary arteries precontracted with PGF_2α (2×10⁻⁶ M). Data are means±s.e.mean.

Figure 3

Concentration-response curves of SPME (10⁻¹⁰–10⁻⁷ M) for EDR under EDC-blockade and for EDC under EDR-blockade in endothelium-intact rabbit intrapulmonary arteries precontracted with PGF_2α (2×10⁻⁶ M). Data are means±s.e.mean (n=9) EDC: SPME was applied in the presence of L-NAME (10⁻⁴ M) and SR-48968 (10⁻⁷ M), which eliminate EDR and EIC, respectively. EDR: SPME was applied in the presence of ozagrel (10⁻⁵ M) and SR-48968 (10⁻⁷ M), which eliminate EDC and EIC, respectively.

Figure 4

Effects of indomethacin (cyclo-oxygenase inhibitor), ozagrel (TXA₂ synthetase inhibitor), AA-861 (5-lipoxygenase inhibitor) and L-NAME (nitric oxide synthase inhibitor) on the EDC and EDR component in the biphasic endothelium-dependent response induced by SPME (10⁻⁷ M) in endothelium-intact rabbit intrapulmonary arteries precontracted with PGF_2α (2×10⁻⁶ M). C=control. Data are means±s.e.mean. ^*P<0.05, ^**P<0.01, Student's t-test for paired data.

Figure 5

Effects of CP-99994 (tachykinin NK₁ receptor antagonist) and SR-48968 (NK₂ receptor antagonist) on the EDC and EDR component in the biphasic endothelium-dependent response induced by SPME (10⁻⁷ M) in endothelium-intact rabbit intrapulmonary arteries precontracted with PGF_2α (2×10⁻⁶ M). C=control. Data are means±s.e.mean. ^*P<0.05, ^**P<0.01, student's t-test for paired data.

Figure 6

Effects of CP-99994 (tachykinin NK₁ receptor antagonist) on the EDR component induced by SPME (10⁻⁷ M) under EDC blockade and the EDC component under EDR blockade in endothelium-intact rabbit intrapulmonary arteries precontracted with PGF_2α (2×10⁻⁶ M). EDR: ozagrel (10⁻⁵ M) and SR-48968 (10⁻⁷ M) were applied to eliminate EDC and EIC, respectively. EDC: L-NAME (10⁻⁴ M) and SR-48968 (10⁻⁷ M) were applied to eliminate EDR and EIC, respectively. C=control. Data are mean±s.e.mean (n=11). ^*P<0.05, ^**P<0.01, Student's t-test for paired data.