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KMID : 0376219850220020257
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Chonnam Medical Journal
1985 Volume.22 No. 2 p.257 ~ p.265
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Effects of d, l, dl-Propranolol on the Changes of Blood Pressure and Heart Rate induced by Isoproterenol in Rabbits
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Abstract
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[ I ] To examine the existence of beta-adrenoceptors which are participating in the regulation of the blood pressure and heart rate in the rabbit brain, effects of intraventricular isoproterenol(ISO) and some beta-receptor antagonists three stereoisomers of propranolol(d, 1, dl-form), pindolol, practolol and sotalolon blood pressure and heart rate were investigated.
1. ISO produced a decrease of blood pressure, small doses of three propranolol isomers produced little changes in blood pressure. Large doses of d-form(2mg) and dl-form(lmg) induced a hypertensive effect. Large doses of 1-form(2mg) induced a hypotensive effect preceded by a transient hypertensive one. Pindolol induced hypotensive effect and practolol and sotalol produced little changes in blood pressure.
2. Heart rate was increased by ISO but all antagonists except sotalol reduced heart rate.
3. Hypotension by ISO was blocked by each of 1, dl-propranolol, pindolol and sotalol. This effect was not affected by d-propranolol and practolol.
4. The tachycardiac effect of ISO was blocked by 1, dl-propranolol, pindolol and sotalol but not affected by d-propranolol and practolol. This effect of ISO, however, was augmented by each of d-propranolol(2mg), practolol(2mg), dlpropranolol(31μg) and pindolol (31μg).
[II ] To compare the properties of central and peripheral receptors on which ISO and three propranolol isomers act, the effect of intravenous ISO(3μg/kg) and three propranolol isomers(2mg/kg) on blood pressure and heart rate were investigated.
1. All of three propranolol isomers produced hypotension and bradycardia but had not hypertensive effect.
2. The hypotensive effect of ISO was abolished and reversed to a slight hypertension by 1-, dl-propranolol and significantly attenuated by d-propranolol.
3. The tachycardiac effect of ISO was blocked by 1-, dl-propranolol but potentiated by d-propranolol.
[ III ] From the above results, it was inferred that in the rabbit brain, there exist beta-adrenoceptors which respond stereospecifically to three forms of propranolol and mediate hypotensive and tachycardiac effects of ISO, and that the properties of peripheral receptor participating in tachycadia by ISO are the same as that of central one, but there is a little difference in the properties of central and peripheral receptors which mediate hypotensive effect of ISO.
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