ISSN:
1440-1681
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
1. Characterization of clonidine which reversed the adrenaline-induced contractions was assessed using the rabbit pulmonary arterial segment.2. Clonidine in high concentrations (10−5-10−4 mol/l) contracted this vascular tissue. Nevertheless, an adrenaline (3 × 10−6mol/l)-induced contraction, which can be markedly depressed by phentolamine, was reversed to relaxation by pre-addition of 3 × 10−5mol/l clonidine. This reversal was abolished by mol/l propranolol, a β-adrenoceptor antagonist.3. The cumulative concentration-contraction curve for adrenaline was shifted to the right by 10−5 mol/l clonidine without further alteration at 10−4 mol/l, suggesting a partial agonistic feature of clonidine for α-adrenoceptors.4. Contractions evoked by 5 × 10−5 mol/l clonidine alone were effectively reduced by prazosin (IC50= 1.7 × 10−7 mol/l) or yohimbine, (IC50= 3.3 × 10−5 mol/l) and those by phenylephrine (10−5 mol/l) were suppressed as well (prazosin, IC50= 3.4 × 10−8 mol/l; yohimbine, IC50= 5.0 × 10−6 mol/l). However, the depolarization-induced contractions with 30 mmol/l KCl were virtually unaltered by both antagonists.5. These results suggest that the reversal action of clonidine on the adrenaline-induced contraction is primarily mediated by a partial agonistic property for postsynaptic α1-adrenoceptors.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1440-1681.1984.tb00264.x
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