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KMID : 0376219800170010099
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Chonnam Medical Journal
1980 Volume.17 No. 1 p.99 ~ p.111
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Relative pre- and postsynaptic potencies of α-adrenoceptor antagonists in the rabbit brain
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Abstract
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1. Pre- and postsynaptic effects of intraventricular(i. vt.) a-adrenoceptor antagonists were compared in the rabbit blood pressure. Antagonism against i.vt. methoxamine-induced hypertension(A), and inhibition of i. vt. clonidineinduced hypotension(B), were taken to indicate post- and presynaptic blockade in the brain respectively.
2. Table 6 in the text shows the doses of the antagonists to antagonize A nad B, and ratio values(A/B) of each antagonist. The antagonists differ in their relative pre- and postsynaptic potencies. For instance, yohimbine and piperoxan preferentially block presynaptic a-receptors, whereas thymoxamine and labetalol preferentially block postsynaptic a-receptors.
3. In reserpinized rabbits i.vt. clonidine produced the pressor response that was inhibited partially by i.vt. thymoxamine.
4. Intraventricular yohimbine and piperoxan produced pressor response in control rabbits, whereas they did not in reserpinized ones.
5. These results suggest that two different types of a-receptors, pre- and postsynaptic a-receptors, are located in the rabbit brain, regulating the blood pressure.
6. The cardiac slowing by clonidine was significantly inhibited by the antagonists which did the depressor response. Methoxamine, however, also tended to produce cardiac slowing, which was not significantly affected by the antagonists affecting the methoxamine- induced hypertension.
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