Inhibitory effects of calcium antagonists on alpha-adrenoceptor-mediated contraction in the human internal mammary artery.
1. The internal mammary artery has become a preferred coronary bypass graft. Sympathomimetic amines are spasmogens for vasospasm and calcium antagonists are frequently administered drugs perioperatively. The effect of calcium antagonists on alpha-adrenoceptor-mediated contraction depends on the subtype of alpha-adrenoceptor and the type of origin of vascular smooth muscle. This study was designed to investigate the effect of calcium antagonists on alpha-adrenoceptor-mediated contraction in the IMA. 2. Human IMA segments taken from 22 patients undergoing IMA--coronary artery bypass grafting were mounted in an organ bath under the physiological pressure determined from their own length-tension curves. 3. Three ring segments were allocated into three groups. One served as a control and the others were treated with clinically related concentrations of nifedipine (20 or 200 nM) for 25 min before concentration-contraction curves to alpha 1-adrenoceptor agonist methoxamine (MO) or full alpha-adrenoceptor agonist noradrenaline (NA) were established. 4. In separate experiments, the concentration-relaxation curves to nifedipine were established in the IMA rings precontracted with MO (30 microM) or NA (10 microM). Glyceryl trinitrate (GTN, 3 microM) was added to further relax the vessels. 5. Pretreatment with nifedipine (200 nM) only slightly inhibited the MO- (1.74 +/- 0.32 vs 2.88 +/- 0.56 g) or NA- (2.43 +/- 0.66 vs 3.60 +/- 0.82 g) induced contraction without statistical significance (P > 0.05). 6. On the other hand, nifedipine only caused 34.49% relaxation in the MO-precontracted and 24.39% relaxation in the NA-precontracted IMAs. In contrast, GTN caused 76.16% (against MO, P < 0.05) or 92.22% (against NA, P < 0.0001) relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)
He
G W
GW
Cardiothoracic Surgery Associates of North Texas, Medical City Dallas Hospital.
Acuff
T E
TE
Ryan
W H
WH
Yang
C Q
CQ
Douthit
M B
MB
Bowman
R T
RT
Mack
M J
MJ
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D004347:Drug Interactions; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008323:Mammary Arteries / Q000187:drug effects* / Q000502:physiology; D008729:Methoxamine / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology*; D005996:Nitroglycerin / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects*
D000316:Adrenergic alpha-Agonists; D005996:Nitroglycerin; D008729:Methoxamine; D009543:Nifedipine; D009638:Norepinephrine