Yonsei Med J.  2009 Jun;50(3):414-421. 10.3349/ymj.2009.50.3.414.

Inhibitory Effect of Fentanyl on Phenylephrine-Induced Contraction of the Rat Aorta

• Park KE
• Sohn JT
• Jeong YS
• Sung HJ
• Shin IW
• Lee HK
• Chung YK

• KMID: 1758571
• DOI: http://doi.org/10.3349/ymj.2009.50.3.414

Abstract

PURPOSE: Fentanyl was reported to inhibit the alpha1-adrenoceptor agonist-induced contraction. The goal of this in vitro study was to identify the alpha1-adrenoceptor subtype primarily involved in the fentanyl-induced attenuation of phenylephrine-induced contraction in isolated endothelium-denuded rat aorta.
MATERIALS AND METHODS
Aortic rings were suspended in order to record isometric tension. Concentration-response curves for phenylephrine (10-9 to 10-5 M) were generated in the presence or absence of one of the following drugs: fentanyl (3x10-7, 10-6, 3x10-6 M), 5-methylurapidil (3x10-8, 10-7, 3x10-7 M), chloroethylclonidine (10-5 M) and BMY 7378 (3x10-9, 10-8, 3x10-8 M). Phenylephrine concentration-response curves were generated in the presence or absence of fentanyl in rings pretreated with either 3x10-9 M prazosin, 10-9 M 5-methylurapidil or 3x10-9 M BMY 7378.
RESULTS
Fentanyl (10-6, 3x10-6 M) attenuated phenylephrine-induced contraction in the rat aorta. 5-Methylurapidil and BMY 7378 produced a parallel rightward shift in the phenylephrine concentration-response curve. The pA2 values for 5-methylurapidil and BMY 7378 were estimated to be 7.71 +/- 0.15 and 8.99 +/- 0.24, respectively. Fentanyl (10-6 M) attenuated phenylephrine-induced contraction in rings pretreated with 10-9 M 5-methylurapidil, but did not alter the rings when pretreated with 3x10-9 M BMY 7378. Pretreatment of the rings with chloroethylclonidine showed a 72.9 +/- 2.3% reduction in phenylephrine-induced maximal contraction.
CONCLUSION
The results suggest that fentanyl attenuates phenylephrine-induced contraction by inhibiting the pathway involved in the alpha1D-adrenoceptor-mediated contraction of the rat aorta.

Keyword

Fentanyl; phenylephrine; 5-methylurapidil; BMY 7378; prazosin; rat aorta

MeSH Terms

Adrenergic alpha-Agonists/*pharmacology
Adrenergic alpha-Antagonists/*pharmacology
Animals
Aorta/*drug effects
Clonidine/analogs & derivatives/pharmacology
Fentanyl/*pharmacology
Male
Phenylephrine/*pharmacology
Piperazines/pharmacology
Rats
Rats, Sprague-Dawley
Vasoconstriction/*drug effects

Figure

• 

  Fig. 1 Effect of fentanyl on the phenylephrine dose-response curve in endothelium-denuded rat aorta. Fentanyl (10-6, 3×10-6 M) produced a significant rightward shift (ED50: *p < 0.05 versus no drug) in the phenylephrine dose-response curve. Data are shown as mean ± SD and expressed as the percentage of maximal contraction induced by isotonic 60 mM KCl (isotonic 60 mM KCl-induced contraction: 100% = 2.62 ± 0.39 g [n = 7], 100% = 2.65 ± 0.33 g [n = 5], 100% = 2.67 ± 0.37 g [n = 7] and 100% = 2.22 ± 0.29 g [n = 6] for the rings not treated with fentanyl, the fentanyl [3×10-7 M], [10-6 M] and [3×10-6 M] pretreated rings, respectively).

• 

  Fig. 2 (A) Effect of 5-methylurapidil (5-MU) on phenylephrine doe-response curve. 5-MU (3×10-8, 10-7, 3×10-7 M) produced a parallel rightward shift (ED50: *p < 0.01 versus no drug, †p < 0.001 versus 3×10-8 M 5-MU, ‡p < 0.05 versus 10-7 M 5-MU) in the phenylephrine dose-response curve in a concentration-dependent manner. Data are shown as mean ± SD and expressed as the percentage of maximal contraction induced by isotonic 60 mM KCl (isotonic 60 mM KCl-induced contraction: 100% = 3.30 ± 0.84 g [n = 5], 100% = 2.82 ± 0.75 g [n = 5], 100% = 2.74 ± 0.52 g [n = 5] and 100% = 2.38 ± 0.71 g [n = 5] for the rings not treated with 5-MU, the 5-MU [3×10-8 M], [10-7 M] and [3×10-7 M] pretreated rings, respectively). (B) A Schild plot was constructed with the concentration ratio (CR: ED50 in the presence and absence of 5-MU) for individual experiments. The slope of the Schild plot for 5-MU was 1.21 ± 0.23 (r2 = 0.69), and the concentration (-log M) of 5-MU necessary to displace the phenylephrine concentration-response curve by twofold was 7.71 ± 0.15.

• 

  Fig. 3 (A) Effect of BMY 7378 on phenylephrine does-response curve. BMY 7378 (3×10-9, 10-8, 3×10-8 M) produced a parallel rightward shift (ED50: *p < 0.01 versus no drug, †p < 0.001 versus 3 ×10-9 M BMY 7378, ‡p < 0.001 versus 10-8 M BMY 7378) in the phenylephrine dose-response curve in a concentration-dependent manner. Data are shown as mean ± SD and expressed as the percentage of maximal contraction induced by isotonic 60 mM KCl (isotonic 60 mM KCl-induced contraction: 100% = 3.03 ± 0.81 g [n = 5], 100% = 2.90 ± 0.31 g [n = 5], 100% = 2.47 ± 0.66 g [n = 5] and 100% = 2.34 ± 0.26 g [n = 5] for the rings not treated with BMY 7378, the BMY 7378 [3×10-9 M], [10-8 M] and [3×10-8 M] pretreated rings, respectively). (B) A Schild plot was constructed with the concentration ratio (CR: ED50 in the presence and absence of BMY 7378) for individual experiments. The slope of the Schild plot for BMY 7378 was 0.87 ± 0.19 (r2 = 0.62), and the concentration (-log M) of BMY 7378 necessary to displace the phenylephrine concentration-response curve by twofold was 8.99 ± 0.24.

• 

  Fig. 4 Effect of chloroethylclonidine (CEC) on phenylephrine dose-response curve in endothelium-denuded rat aorta. The first phenylephrine dose-response curves were obtained before (no drug) exposure to 10-5 M CEC. After aortic rings were pretreated with 10-5 M CEC for 20 min and washed intensively, second dose-response curves for phenylephrine were obtained. CEC (10-5 M) inhibited maximal contraction induced by phenylephrine (*p < 0.0001 versus no drug). Data are shown as mean ± SD and expressed as the percentage of the first phenylephrine-induced maximal contraction (phenylephrine-induced maximal contraction: 100% = 3.9 ± 0.16 g [n = 4] for the rings with no drug).

• 

  Fig. 5 Effect of 10-6 M fentanyl on phenylephrine dose-response curve in rings pretreated with 10-9 M 5-methylurapidil. Fentanyl (10-6 M) attenuated (ED50: *p < 0.01 versus 10-9 M 5-methylurapidil alone) phenylephrine-induced contraction compared with rings pretreated with 10-9 M 5-methylurapidil alone. Data are shown as mean ± SD and expressed as the percentage of maximal contraction induced by isotonic 60 mM KCl (isotonic 60 mM KCl-induced contraction: 100% = 2.71 ± 0.68 g [n = 9] and 100% = 2.98 ± 0.43 g [n = 9] for the rings not treated with fentanyl and the fentanyl [10-6 M] pretreated rings, respectively).

• 

  Fig. 6 Effect of 10-6 M fentanyl on the phenylephrine dose-response curve in rings pretreated with 3×10-9 M BMY 7378. Fentanyl (10-6 M) did not significantly alter pheny lephrine-induced contraction compared with rings pretreated with 3×10-9 M BMY 7378 alone. Data are shown as mean ± SD and expressed as the percentage of maximal contraction induced by isotonic 60 mM KCl (isotonic 60 mM KCl-induced contraction: 100% = 2.89 ± 0.33 g [n = 7] and 100% = 2.72 ± 0.36 g [n = 7] for the rings not treated with fentanyl and the fentanyl [10-6 M] pretreated rings, respectively).

• 

  Fig. 7 Effect of fentanyl on the phenylephrine dose-response curve in rings pretreated with 3×10-9 M prazosin. Fentanyl (3×10-6 M) had no effect on the phenylephrine dose-response curve in the rings pretreated with 3×10-9 M prazosin. Data are shown as mean ± SD and expressed as the percentage of maximal contraction induced by isotonic 60 mM KCl (isotonic 60 mM KCl-induced contraction: 100% = 3.06 ± 0.32 g [n = 7] and 100% = 3.03 ± 0.55 g [n = 7] for the rings not treated with fentanyl and the fentanyl [3×10-6 M] pretreated rings, respectively).

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