A new experimental approach in endothelium-dependent pharmacological investigations on isolated porcine coronary arteries mounted for impedance planimetry

1 The aim of this study was to investigate whether the balloon-based impeda nce planimetry technique could be a useful tool in endothelium-dependent in vestigations. 2 Porcine large coronary arteries contracted with prostaglandin F-2 alpha ( PGF(2 alpha), 10 mu M) did not relax to bradykinin (0.1 nM-0.1 mu M), but d id relax to sodium nitroprusside (SNP, 10 mu M). However, after eversion of the segments, bradykinin induced relaxations with pD(2) values and maximal responses of 8.78 +/- 0.09 and 75 +/- 2% (n = 6), respectively. 3 Incubation with captopril (1 mu M) did not reveal a relaxation to bradyki nin in the normal vessel configuration and had no influence on the concentr ation-relaxation relationship in everted segments. 4 Lowering the luminal pressure in contracted segments from 131 +/- 5 mmHg (isometric, n = 5) to 60 mmHg (isobaric, n = 5) did not facilitate the acti on of bradykinin. 5 Eversion of segments did not influence the concentration-response relatio nship for K+ (4.7-125 mM), PGF(2 alpha) (0.3-30 mu M), and SNP (30 nM-30 mu M), although the time-courses of responses were faster when the agents wer e added from the intimal compared to the adventitial side of the preparatio n. 6 In the same everted segment contracted with PGF(2 alpha), the concentrati on-response relationship for bradykinin was not different under isometric a nd isobaric conditions. 7 These results indicate that, (1) reduced endothelium-dependent relaxation s to adventitially administered substances can be ascribed to a diffusion b arrier in the vessel wall, while enzymatic degradation, luminal pressure an d precontractile responses seem not to play a role, (2) impedance planimetr y applied to everted cylindrical segments could be a useful experimental ap proach in pharmacological studies of endothelium-dependent responses under isobaric and isometric conditions.