The Influence of Calcium Channel Antagonists on Isolated Human Distal Radial Arteries

An alternative agent for radial arterial graft spasm: application of topical iloprost

OBJECTIVE

This study is planned bringing about a new choice for the prophylaxis of RA spasm which is topical iloprost and compares its efficacy with papaverine and diltiazem.

DESIGN

Twenty eight CABG patients with RA grafts were categorized into four groups by taking into account the topical vasodilator (papaverine, diltiazem, iloprost and saline) that was utilized during harvesting. Arterial segments were separated into four rings and were than soaked with KCL, norepinephrine, phenylephrine and serotonin. Then, acetylcholine was given to induce relaxation and the preparations were put to rest for 10 minute.

RESULTS

The contraction response achieved by the vasoreactive agents was most effectively inhibited by papaverine. The effectiveness of the response obtained by iloprost was similar to that of papaverine and significantly stronger than that of diltiazem. Especially at high vasoreactive substance concentrations, diltiazem had a contraction close to that of the control while the protective effect was weaker than those of papaverine and iloprost.

CONCLUSION

Iloprost can be recommended as a strong alternative to the topical agents used for preventing arterial graft spasm.

Intraindividual comparison of human radial and internal thoracic arteries in vitro and the effect of preoperative calcium blocker therapy

The patency rate of radial artery (RA) conduits is considerably lower than that of internal thoracic artery (ITA) grafts and the evidence suggests that this is due to a clinically suspected higher incidence of vasospasm. The aim of this study was, therefore, to compare intraindividually the pharmacological reactivity of RA with that of ITA. Both RA and ITA were taken from the same patients and investigated in parallel. Changes in tone were monitored isometrically on ring preparations from both arteries in organ baths with modified Krebs-Henseleit solution containing 1.25 mm calcium chloride at 1 g passive preload. In intraindividual comparisons maximal receptor-mediated contractile responses to noradrenaline and endothelin-1 and endothelium-dependent acetylcholine-induced relaxant responses revealed no differences between both arteries. By contrast, depolarization-induced contractions to potassium chloride (KCl) appeared to be significantly higher in RA than in ITA. Further analysis, however, revealed that this difference was due to preoperative calcium entry blocker (Ca(2+)eB) therapy. Compared with control tissues, maximal responses to KCl were significantly attenuated in the ITA but unchanged in RA when arteries were obtained from patients with preoperative Ca(2+)eB therapy. The present results suggested that functional responses to pharmacological stimuli of both RA and ITA were quite similar. Preoperative Ca(2+)eB therapy, however, attenuated markedly responses to KCl of the ITA leaving those of RA unchanged. These results, demonstrating a lower sensitivity to Ca(2+)eB of RA, therefore suggested that in addition to Ca(2+)eB other classes of drug may be more effective at reducing the propensity of RA conduits to vasospasm.

Relaxant responses to calcium channel antagonists and potassium channel opener in human saphenous vein

1.-- As shown in a parallel study the magnitude of depolarization induced in human saphenous vein by raising external potassium ([K(+)](e)) falls markedly below the theoretical values predicted by the Goldman-Hodgkin-Katz equations. This anomaly prompted us to re-examine the relaxant actions of L-type (nifedipine) and T-type (mibefradil) Ca(2+) channel antagonists, and relaxant and electrophysiological effects of the K(+) channel opener, pinacidil, on saphenous veins contracted by the elevation of [K(+)](e). 2.-- Nifedipine produced concentration-dependent relaxations in tissues contracted at various high [K(+)](e). In tissues contracted with 20 mm [K(+)](e), the pIC(50) for nifedipine was significantly (8.20 +/- 0.05; n = 6; mean +/- SEM; P < 0.05) greater than in tissues contracted with > or =40 mm [K(+)](e). 3.-- Tissues contracted with 20 mm [K(+)](e) also relaxed in response to mibefradil (pIC(50) = 6.1 +/- 0.14) and pinacidil (pIC(50) = 6.45 +/- 0.08), the latter being almost completely reversed (93.4 +/- 9.9%) by addition of glibenclamide (10 microm). 4.-- The resting E(m) of smooth muscle cells of saphenous vein was -77.0 +/- 0.7 mV (n = 52), and 20 mm [K(+)](e) produced a modest but significant depolarization to -73.0 +/- 0.7 mV (n = 52). Incubation with pinacidil plus 20 mm [K(+)](e) resulted in a significant hyperpolarization of the E(m) to -82 +/- 0.6 mV (n = 52). 5.-- N(omega)-nitro-L-arginine methyl ester did not impede the relaxant responses of nifedipine, mibefradil or pinacidil. 6.-- In conclusion, the relaxant effects of nifedipine and pinacidil (i) occurred at an E(m) distinctly below the presumed threshold for the opening of the classic (Ca(V)1.3alpha(1)) L-type Ca(2+) channels, and (ii) did not depend on generation of nitric oxide.