The Effects of Etomidate on the Isolated Porcine Coronary Artery / 대한마취과학회지

BACKGROUND: Etomidate produces minimal cardiovascular effects in clinical uses but their effects on the porcine coronary arteries are not well known yet. We studied the direct effects of etomidate on porcine coronary arterial tone and the underlying mechanism of its vascular relaxation. METHODS: Porcine coronary arterial ring segments (3-4 mm) with or without endothelium were suspended in modified Krebs solution (37oC) and preconstricted with K+ 40 mM. Changes in tension were measured following cumulative administrations of etomidate (10(-5), 5 x 10(-5) and 10(-4) M). Relaxation caused by etomidate (10(-4)M) were measured in the presence of either NG-nitro-L-arginine methyl ether (L-NAME 10(-5)M, n = 13), indomethacin (2.8 x 10(-5)M, n = 12), methylene blue (2 x 10(-5)M, n = 12), tetraethylammonium (TEA, KCa2+ blocker, 20 mM, n = 11), glibenclamide (n = 13) 2.5 x 10(-5)M or 4-aminopyridine (4-AP, K+ DR blocker, 10 4 M, n = 12). Effects of etomidate on Ca2+ influx through the voltage operated channel (VOC) of the vascular cells were also evaluated. RESULTS: Arterial reings were relaxed by etomidate in a concentration-dependent manner and these effects were not affected by endothelium. In the etomidate pretreated group, arterial ring in a calcium-free solution showed no contraction with KCl 40 mM, but the contraction after the administration of calcium 2.5 mM less than without etomidate group (47.2 +/- 8.7% vs 97.7 +/- 10.6%). The other group, not pretreated with etomidate, showed the same vascular tone of the control group in a slow upstroke manner with calcium administration. Pretreatment with either L-NAME, indomethacin and methylene blue did not affect etomidate-induced vasorelaxation. The TEA, glibenclamide and 4-AP pretreated groups also did not affect the vascular relaxation. CONCLUSIONS: Etomidate relaxes the porcine coronary artery in a concentration-dependent manner withor without endothelium, via inhibition of Ca2+ influx through the voltage-operated Ca2+ channel.

Effects of Amrinone on the Vascular Tension of the Isolated Rabbit Pulmonary Artery / 대한마취과학회지

BACKGROUND: Amrinone is a noncatecholamine, nonglycoside compound, which is known to possess both cardiac inotropic and vasodilatory actions. This drugs has been increasingly used in clinical practice for the management of low cardiac output syndrome during anesthesia, particularly for patients associated with right heart failure and pulmonary hypertension. The aim of this study was to explore the direct vasoactive effect of amrinone and its action mechanisms in the isolated rabbit pulmonary artery. METHODS: The rabbits' pulmonary arteries were dissected free and cut into rings (3 4 mm) and mounted for isometric tension in a tissue chamber. The effects of amrinone (5 10 6 5 10 4 M) on the vascular tension were assessed in the by KCl (40 mM)- or norepinephrine (NE, 10 6 M)- precontracted pulmonary arterial rings with or without endothelium. Also effects of K channel blockers (tetraethyl ammonium 20 mM, glybenclamide 2.5 10 5 M, 4-aminopyridine (4-AP) 5 10 4 M), protein kinase A & G inhibitor (H8), L-NAME, methylene blue and indomethacin on the amrinone- induced vascular responses were investigated. Also studied was effects of amrinone on the Ca2 influx through voltage operated channel (VOC) and receptor operated channel (ROC) of the vascular cells. RESULTS: Amrinone produced vasorelaxation of KCl- or NE-precontracted pulmonary artery in a dose-dependent fashion. The amrinone-induced vasorelaxation was not affected by the denudation of the endothelium. Pretreatment with L-NAME and methylene blue did not affect the vasodilatory effect of amrinone, suggesting that nitric oxide is not involved. Following pretreatment with indomethacin (a cyclooxygenase inhibitor) or K channel blockers, the amrinone-induced vasorelaxation was not altered. After exposure to Ca2 free solution, amrinone attenuated the KCl- or NE-induced contraction even in the presence of Ca2 , implying that VOC and ROC are blocked by amrinone. On the other hand, protein kinase A blocker (H8) completely abolished the amrinone-induced relaxation in the KCl-precontracted pulmonary artery. CONCLUSIONS: These findings suggest that the amrinone-induced vasorelaxations result from inhibition of VOC and ROC as well as from the activation of protein kinase A in the isolated rabbit pulmonary artery.