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. 2008 Apr;153(8):1623-30.
doi: 10.1038/bjp.2008.35. Epub 2008 Feb 25.

The Antiarrhythmic Effect of Centrally Administered Rilmenidine Involves Muscarinic Receptors, Protein Kinase C and Mitochondrial Signalling Pathways

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The Antiarrhythmic Effect of Centrally Administered Rilmenidine Involves Muscarinic Receptors, Protein Kinase C and Mitochondrial Signalling Pathways

M Iwasaki et al. Br J Pharmacol. .
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Abstract

Background and purpose: We have previously demonstrated that stimulation of imidazoline receptors in the CNS prevented halothane-adrenaline arrhythmias during halothane anaesthesia and that stimulation of the vagus nerve may be critical to this effect. However, details of the mechanism(s) involved are not yet available. The present study was designed to examine the role of muscarinic receptors, protein kinase C (PKC), ATP-sensitive potassium channels (K(ATP)) and the mitochondrial permeability transition pore (MPTP) in the antiarrhythmic effect of rilmenidine, an imidazoline receptor agonist.

Experimental approach: Rats were anaesthetized with halothane and monitored continuously for arterial blood pressure and premature ventricular contractions. The arrhythmogenic dose of adrenaline was defined as the lowest dose producing three or more premature ventricular contractions within a 15-s period. We confirmed that centrally administered rilmenidine prevented halothane-adrenaline arrhythmias and then examined the antiarrhythmic effect of rilmenidine in the presence of atropine methylnitrate, a muscarinic receptor antagonist, calphostin C, a PKC inhibitor, HMR-1098, a sarcolemmal K(ATP) inhibitor, 5-hydroxydecanoic acid, a mitochondrial K(ATP) inhibitor or atractyloside, an MPTP opener.

Key results: The antiarrhythmic effect of rilmenidine was significantly inhibited by atropine methylnitrate, calphostin C, 5-hydroxydecanoic acid and atractyloside, but the effects of HMR-1098 in our model were not clear.

Conclusions and implications: The present results suggest that muscarinic receptors, PKC, mitochondrial K(ATP) channels and MPTP may be crucial components of the mechanism involved in the antiarrhythmic effect of rilmenidine given into the CNS.

Figures

Figure 1
Figure 1
Arrhythmogenic dose and plasma concentration of adrenaline in the presence of intracisternal (i.c.) rilmenidine (0, 0.01, 0.05 and 0.1 μg kg−1) in the intact, bilaterally vagotomized or atropine methylnitrate (5 mg kg−1, i.v.)-treated rats during halothane anaesthesia. The values are expressed as mean±s.d. and the number of observations is shown in parentheses. *P<0.05, compared with the rilmenidine 0 μg kg−1 value. Ril 0.1+vagotomy: i.c. rilmenidine 0.1 μg kg−1 and bilateral vagotomy. Ril 0.1+AT: i.c. rilmenidine 0.1 μg kg−1 and atropine methylnitrate (5 mg kg−1).
Figure 2
Figure 2
The effect of calphostin C on arrhythmogenic dose and plasma concentration of adrenaline in the presence of intracisternal (i.c.) rilmenidine (0 and 0.1 μg kg−1) during halothane anaesthesia. The values are expressed as mean±s.d. and the number of observations is shown in parentheses. *P<0.05, compared with the rilmenidine 0 μg kg−1 value in each treatment. Control: no calphostin C pretreatment. The data are quoted from Figure 1. Calphostin C: calphostin C pretreatment.
Figure 3
Figure 3
The effect of 5-hydroxydecanoic acid (5-HD) and HMR-1098 on arrhythmogenic dose and plasma concentration of adrenaline in the presence of intracisternal (i.c.) rilmenidine (0 and 0.1 μg kg−1) during halothane anaesthesia. The values are expressed as mean±s.d. and the number of observations is shown in parentheses. *P<0.05, compared with the rilmenidine 0 μg kg−1 value in each treatment. Control: no ATP-sensitive potassium channel blocker pretreatment. The data are quoted from Figure 1. 5-HD: 5-HD pretreatment. HMR-1098: HMR-1098 pretreatment.
Figure 4
Figure 4
The effect of atractyloside on arrhythmogenic dose and plasma concentration of adrenaline in the presence of intracisternal (i.c.) rilmenidine (0 and 0.1 μg kg−1) during halothane anaesthesia. The values are expressed as mean±s.d. and the number of observations is shown in parentheses. *P<0.05, compared with the rilmenidine 0 μg kg−1 value in each treatment. Control: no atractyloside pretreatment. The data are quoted from Figure 1. Atractyloside: atractyloside pretreatment.

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