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The effect of some alpha-adrenoceptor antagonists on spontaneous myogenic activity in the rat portal vein and the putative involvement of ATP-sensitive K+ channels.

Abstract：

:In the present study we showed that the alpha-adrenoceptor antagonists phentolamine, yohimbine, prazosin, corynanthine and idazoxan, when cumulatively applied in high concentrations (1-100 mumol/l), can increase spontaneous myogenic activity in the rat portal vein. 5-Methyl-urapidil and rauwolscine were ineffective in this respect. Pretreatment with phenoxybenzamine in a concentration of 1 mumol/l (20 min), which results in alkylation of all functional alpha-adrenoceptors in the rat portal vein, was unable to antagonize the increase in spontaneous myogenic activity elicited by phentolamine. Antazoline (1-100 mumol/l), a H1 antagonist and 2-substituted imidazoline which is devoid of alpha-adrenoceptor blocking properties, exhibited similar effects on spontaneous myogenic activity as its structurally closely related analogue phentolamine. Since phentolamine is reported to interact with ATP-sensitive K+ channels we investigated the role of K+ channels in more detail. The K+ channel openers cromakalim and diazoxide elicited a decrease in spontaneous myogenic activity. Glibenclamide (0.3-3 mumol/l), a selective blocker of ATP-sensitive K+ channels in cardiac and pancreatic tissues, and phentolamine (1-10 mumol/l) shifted the concentration-response curves of cromakalim and diazoxide concentration dependently to the right. Yohimbine showed only a modest effect in the highest concentration (100 mumol/l) applied. E-4031 (0.01-0.3 mumol/l), a sotalol derivative and one of the most selective blockers of the delayed rectifier current (Ik) in cardiac tissue, was a potent contractile agent when added to the rat portal vein in the same way as the alpha-adrenoceptor antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)

journal_name

Eur J Pharmacol

journal_title

European journal of pharmacology

authors

Schwietert R,Wilhelm D,Wilffert B,Van Zwieten PA

doi

10.1016/0014-2999(92)90267-8

keywords:

subject

Has Abstract

pub_date

1992-01-28 00:00:00

pages

87-95

issue

eissn

0014-2999

issn

1879-0712

pii

0014-2999(92)90267-8

journal_volume

211

pub_type

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The effect of some alpha-adrenoceptor antagonists on spontaneous myogenic activity in the rat portal vein and the putative involvement of ATP-sensitive K+ channels.