EDHF, NO and a prostanoid: hyperpolarization-dependent and -independent relaxation in guinea-pig arteries

The contribution of endothelium-derived hyperpolarizing factor (EDHF), nitric oxide (NO) and a prostanoid (PG) to endothelium-dependent hyperpolarization and relaxation were assessed in coronary and mammary arteries of guinea-pigs by integration of the responses evoked during discrete applications of acetylcholine (ACh). The results of this integration approach were compared with those using traditional peak analysis methods. N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM) and indomethacin (1 microM), alone or in combination, were without effect on peak hyperpolarizations or relaxations while they markedly reduced the integrated responses in both arteries. Integrated responses attributed to NO and PG were larger than those attributed to EDHF in the coronary artery (at 2 microM ACh, hyperpolarization (mV s): NO, 4200+/-91; PG, 5046+/-157; EDHF, 1532+/-94; relaxation (mN s mm(-1)): NO, 2488+/-122; PG, 2234+/-96; EDHF, 802+/-54). Integrated responses attributed to NO, PG and EDHF were similar in the mammary artery (at 2 microM ACh, hyperpolarization: NO, 347+/-69; PG, 217+/-49; EDHF, 310+/-63; relaxation: NO, 462+/-94; PG, 456+/-144; EDHF, 458+/-40). Gilbenclamide (1 microM) all but abolished the hyperpolarization attributable to NO and PG but not EDHF in both arteries allowing assessment of the role of the hyperpolarization in relaxation. Gilbenclamide was without effect on the integrated relaxation due to NO but significantly reduced the relaxation associated with PG in the two arteries. In conclusion, integration of the responses enabled a more complete assessment of the contribution of EDHF, NO and PG to endothelium-dependent responses, which were strikingly different in the two arteries. There is commonality in the role of hyperpolarization in relaxation in both arteries: EDHF-dependent relaxation is strongly dependent on hyperpolarization; hyperpolarization plays an important role in PG relaxation, whereas it has a small facilitatory role in NO-dependent relaxation.