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KMID : 0376219690060020289
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Chonnam Medical Journal
1969 Volume.6 No. 2 p.289 ~ p.300
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Negative Chronotropic Effect of Sympathomimetic Amines on Isolated Atria of the Tortoise and Frog.
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Abstract
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1) Effects of cumulative doses(10^(-7), 10^(-5), 10^(-5), 10^(-4), 5×10^(-4) g/㎖) of sympathomimetic amines, isoproterenol(ISP), norepinephrine(NE), epinephrine(E), phenylephrine(PE) and methoxamine(ME), on the atrial rate of tortoise and frog were investigated in the isolated atrial preparations of tortoise and frog.
2) The tortoise atria reacted with rate increase to the doses up to 10^(-6)g/㎖ of NE, E, and ISP. Increasing the doses to 10^(-5)g/㎖ produced no further increase. When the doses of NE and E were elevated to 10^(-4) g/㎖ the atrial rate decreased below the original rate. In the case of ISP, the elevation of the dose to the same extent did not cause decrease of the rate below the original rate. PE was ineffective in producing rate change. ME elicited rate decrease with doses of above 10^(-6) g/㎖.
3) The atrial rate of frog was scarcely increased be NE, but decreased to below the original rate with doses of above 10^(-6) g/㎖. E produced rate increase with doses up to 10^(-46 g/㎖, and produed rate decrease below the original rate when the dose was further elevated. ISP produced slight rate increase to the doses of 10^(-5) g/㎖, Increasing the doses of ISP above 10^(-5) g/㎖ tended to decrease the rate, but the rate did not fall below the original rate.
4) In atria of both species NE and E elicite no rate increase but definite decrease in the presence of 10^(-5) g/㎖ of ISP. The rate decreasing potency of NE was greater than that of E.
5) Propranolol, an adrenergic beta receptor antagonist, produced no distruct increase on the actions of cumulatiove doses of NE and E, but this inhibited the rate decreasing effect of both amines which was observed in the presence of ISP
6) Pretreatment of the tortoise atria with dihydroergotoxine, an adrenergic alpha antagonist, changed the rate response to NE and E. In this state NE and PE produced no rate increase but rate decrease. ISP was ineffective in producing rate change under the influence of this agent.
7) In the atria of both species pretreated with desmethylimipramine, NE, E, and ISP produced no rate increase but rate decrease. This rate decrease due to ISP was reversed to rate increase by propranolol. The rate decrease due to NE and E was scarcely affected by propranolol.
8) It was discussed that the negative chronotropic effect of sympathomimetic amines was probably due to activation of beta receptor in the auricular tissues. The sensitivity of this type of beta receptor to various sympathomimetic amines seemed to be different from that of the well known beta receptor which assciated with rate increase. The presence of the adrenergic alpha receptor in the auricular tissues of tortoise, which participated in the rate increase, was also suggested.
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KEYWORD
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