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KMID : 0371919900030010035
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Journal of Wonju College of Medicine
1990 Volume.3 No. 1 p.35 ~ p.42
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Abstract
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The presence and role of cardiac α-adrenoceptor was investigated in isolated rat right and left atrial preparations. Left atrial contraction was induced by electrical field stimulation (1 Hz, 0.5 msec, supramaximal voltage) through platinum electrodes.
The results were as follows;
1. Phenylephrine (10^(-6), 10^(-5) M), isoproterenol (10^(-9), 10^(-8) M) increased the contractile tension in spontaneously beating right atrium and field stimulated left atrium in a dose dependent manner.
2. Propranolol (10^(-5) M) pretreatment antagonised only partly the phenylephrine-induced increase of contractile tension in right and left atrium, while norepinephrine-and isoproterenol-induced contractile increases were completely blocked by propranolol pretreatment. Tolazoline (3X10^(-5) M) pretreatment also significantly blocked the phenylephrine-induced increase of contractile tension. But contractile tension increase induced by norepinephrine and isoproterenol were never affected by tolazoline pretreatment.
3. Prazosin (10^(-5) M) pretreatment elicited more significant antagonism than tolazoline pretreatment on phenylephrine-induced atrial tension increases. Combined pretreatment of propranolol with prazosin completely abolished the phenylephrine-induced atrial tension increase.
4. After incubation in the Tyrode solution containing caffeine (2 mM), the resting contractile tension of both right and left atrium was increased. Addition of phenylephrine caused only slight increases in basal tonus.
From these above results, it is suggested that rat atrium has α₁-receptor which induces positive inotropy, and the increase of calcium release from sarcoplasmic reticulum is regarded as underlying mechanism for α-receptor-induced positive inotropy.
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