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J Thorac Cardiovasc Surg 1996;112:542-544
© 1996 Mosby, Inc.
BRIEF COMMUNICATIONS |
Athens and Augusta, Ga.
This work was supported by a grant-in-aid from the American Heart Association/Georgia Affiliate.
Received for publication July 28, 1995 Accepted for publication Dec. 19, 1995. Address for reprints: Randall L. Tackett, PhD, Department of Pharmacology and Toxicology, College of Pharmacy, University of Georgia, Athens, GA 30602-2356.
Dyes, such as methylene blue, are used during vascular surgery to aid in the visualization and orientation of the blood vessel. Although methylene blue dye is believed to be innocuous, we
1 recently demonstrated that extravascular application of 1% methylene blue impairs both endothelium-dependent and endothelium-independent vasorelaxation. The present study investigated Evans blue and gentian violet as alternative surgical marker dyes to methylene blue.
Human saphenous veins were cut into 2 to 4 mm rings, carefully swabbed with 0.5% Evans blue, 1.0% gentian violet, or Krebs buffer, and incubated in 20 ml of buffer at 25º C for 45 minutes. The vascular rings were then suspended in 10 ml tissue baths containing Krebs buffer, and dose-response curves to acetylcholine, isoproterenol, ve rapamil, and sodium nitroprusside were performed as previously described. 1
Vascular rings were assayed in duplicate and averaged to yield a single n value. All statistical analyses were performed with the n values representing the number of patients. Differences were assayed by a one-way analysis of variance followed by a Bonferroni t test for multiple comparisons. All data are presented as the mean ± standard error of the mean. Only differences with a p value < 0.05 were deemed as statistically significant.
Potassium chloride (70 mmol/L) produced a contraction of 1.45 ± 0.36 gm in control rings, which was not significantly different from that observed in rings subjected to Evans blue (1.92 ± 0.48 gm) or gentian violet (1.81 ± 0.40 gm). Phenylephrine (10-5 mol/L) also produced a comparable constriction (1.73 ± 0.52 gm), which was unaffected by exposure to either Evans blue or gentian violet–treated tissue.
Acetylcholine, which assessed endothelium-dependent responses, produced a dose-dependent vasodilation with the nadir at -54% ± 11%, which was unaffected by exposure to Evans blue (Fig. 1, A). Sodium nitroprusside was used to assess endothelium-independent vasodilation. As seen in Fig. 1, B, 100% relaxation was achieved in response to sodium nitroprusside in control vein segments and segments exposed to Evans blue. Verapamil was used to assess calcium-mediated responses. As seen in Fig. 1, C, no significant differences were noted between control vessels and those treated with Evans blue. Fig. 1, D, shows that the vasodilatory responses to isoproterenol mediated through ß2-adrenergic receptors was unaffected by Evans blue treatment.
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1
Methylene blue dye has several actions that could adversely affect vascular reactivity, including inhibition of soluble guanylate cyclase 2 and production of superoxide. 3
The pharmacologic actions of Evans blue and gentian violet have not been studied extensively and thus remain relatively poorly understood. Gentian violet is best known as a topical antimicrobial agent that irreversibly binds microbial deoxyribonucleic acid and directly inhibits replication. 4 Evans blue is a biologic stain whose pharmacologic effects have not been extensively studied, but it is commonly used as a diagnostic agent for the determination of plasma volume. 5
The reason for inhibition of the sodium nitroprusside response by gentian violet is unclear. Gentian violet is metabolized to a reactive intermediate or free radical that could act at the vascular smooth muscle to inhibit the response. However, this is unlikely inasmuch as this mechanism would also interfere with the acetylcholine-mediated vasodilation. A more plausible explanation would be the formation of a reactive intermediate that interacts directly with the sodium nitroprusside molecule.
In conclusion, although methylene blue has been used as a marker dye, our studies suggest that it is inappropriate for marking vascular grafts. Evans blue did not adversely affect vasodilation to any agent and thus could be used as an alternative to methylene blue without fear of affecting graft reactivity. Gentian violet also appears to be a better alternate to methylene blue. However, we did observe a decrease in endothelium-independent vasodilation, a factor that should be considered when this agent is used.
Footnotes
From the University of Georgia, College of Pharmacy, Department of Pharmacology and Toxicology, Athens,a the Medical College of Georgia, Department of Thoracic and Cardiac Surgery, Augusta,b and the University Hospital, Department of Surgery, Augusta, Ga.c 
References
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