The inhibitory action of protamine on human internal thoracic artery contractions: the effect of free hemoglobin.
OBJECTIVE
We investigated the mechanism of the protamine action and the effects of free hemoglobin on protamine-induced responses in endothelium-denuded and-intact human internal thoracic artery (ITA) rings precontracted with phenylephrine (PE) or high KCl.


METHODS
Samples of redundant ITA obtained from patients undergoing a coronary artery bypass graft surgery were cut into 3 mm wide rings and suspended in 20 ml organ baths. Isometric tension was continuously measured with an isometric force transducer connected to a computer-based data acquisition system.


RESULTS
Acetylcholine (Ach, 10(-8)-10(-5) M) caused a concentration-dependent relaxation of PE-precontracted ITA rings. Free hemoglobin (0.1 and 0.5 microM) produced a concentration-dependent and significant decrease in sensitivity (pD(2)) and maximal contractility (E(max)) in response to Ach in PE-precontracted ITA rings (P<0.0001). Protamine (50-800 microg/ml), free hemoglobin (0.1 and 0.5 microM), nitric oxide (NO) blocker N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM) or soluble guanylate cyclase inhibitor methylene blue (10 microM) administration did not cause a significant alteration on basal tonus of endothelium-intact or -denuded ITA rings. Protamine (50-800 microg/ml) induced concentration-dependent relaxation responses in ITA rings precontracted by either PE or high KCl. There was no difference in sensitivity or maximal response to protamine between the endothelium-intact and -denuded rings. Incubation of endothelium-intact or -denuded ITA rings with L-NAME or free hemoglobin or methylene blue did not cause a significant inhibition on relaxation responses to protamine. ITA ring contractions induced by stepwise addition of calcium to high KCl solution with no calcium were almost completely inhibited by protamine (P<0.0001).


CONCLUSIONS
It was suggested that protamine induced relaxation responses in human ITA rings is not NO- or endothelium-dependent but seems to depend on the interactions of protamine with calcium influxes and/or calcium release from intracellular stores in this tissue.
Golbasi
Ilhan
I
Department of Cardiovascular Surgery, Akdeniz University Medical Faculty, 07070, Antalya, Turkey. golbasi@med.akdeniz.edu.tr
Nacitarhan
Cahit
C
Ozdem
Sadi
S
Turkay
Cengiz
C
Karakaya
Hanife
H
Sadan
Gulay
G
Bayezid
Omer
O
D002118:Calcium / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D008751:Methylene Blue / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D010656:Phenylephrine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D011479:Protamines / Q000494:pharmacology*; D013895:Thoracic Arteries / Q000187:drug effects* / Q000502:physiology; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology*
D006454:Hemoglobins; D011479:Protamines; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D010656:Phenylephrine; D011189:Potassium Chloride; D019001:Nitric Oxide Synthase; D006162:Guanylate Cyclase; D002118:Calcium; D008751:Methylene Blue; D019331:NG-Nitroarginine Methyl Ester