Aug 1, 1976

Stereoselective and calcium-dependent contractile effects of narcotic antagonist analgesics in the vascular smooth muscle of the rat

The Journal of Pharmacology and Experimental Therapeutics
C H Lee, B A Berkowitz


In patients, pentazocine administered i.v. can have an unusual action for a strong analgesic-an elevation of blood pressure. The objective of this study in rats was to better quantify and explain the molecular mechanism for the vascular action of l-pentazocine and compare it with other analgesics and narcotic antagonists. In anesthetized rats, l-pentazocine (0.3-3 mg/kg i.v.) elevated blood pressure and this effect was potentiated in pithed rats. The contraction appeared to be nonadrenergic as it was not blocked by the alpha blocker, phenoxybenzamine. In vitro, morphine (ED50 = 4 X 10(-5) M) and the l-isomers of pentazocine (ED50 = 8 X 10(-6) M) contracted the spirally cut aortic strip. The l-isomers were approximately 5 times more potent than their d-enantiomers. Contraction of the aorta by l-pentazocine was not inhibited by dibenamine, atropine, diphenhydramine, pyrilamine or indomethacin nor potentiated by propranolol. On the other hand, not only was the contraction highly dependent on the concentration of calcium in the bath but it was also blocked by verapamil and SKF-525A, drugs known to inhibit transmembrane calcium influx. Naloxone (3 X 10(-4) to 1 X 10(-3) M), which produced no contractile effect by itself, reduced aor...Continue Reading

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Mentioned in this Paper

Molecular Stereochemistry
Phenoxybenzamine Hydrochloride
Diastolic Blood Pressure
Smooth Muscle
Norepinephrine Receptors
Spinal Cord
Descending Aorta
Narcotic Antagonists

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