Summary
In dogs (pentobarbitone, 25 mg/kg) the brain was removed rostrally to the pons, leaving the cerebellum intact (decerebrate animals). In other animals the cerebellum was additionally removed (bulbar animals). In all animals β-adrenoceptors were blocked by toliprolol (5 mg/kg s.c.). Angiotensin (0.025–0.3μg/kg) was repeatedly injected i.v. and the resulting maximal reflex bradycardia was recorded. Intracisternal (i.ci.) injection of clonidine, 0.5 or 1 μg/kg, in decerebrate or i.v. injection of 10 or 30 μg/kg in bulbar animals significantly facilitated the reflex bradycardia. This effect was antagonised by a subsequent injection of piperoxan, 50 μg/kg i.ci. in decerebrate or 1 mg/kg i.v. in bulbar animals. It is concluded that the facilitatory action of clonidine is mediated by α-adrenoceptors within the medulla oblongata.
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References
Crill, W. E., Reis, D. J.: Distribution of carotid sinus and depressor nerves in cat brain stem. Amer. J. Physiol. 214, 269–276 (1968)
Fuxe, K.: Evidence for the existence of monoamine neurons in the central nervous system. IV. The distribution of monoamine terminals in the central nervous system. Acta physiol. scand. 64 (Suppl. 247), 37–85 (1965)
Hockman, Ch. H., Talesnik, J., Livingston, K. E.: Central nervous system modulation of baroreceptor reflexes. Amer. J. Physiol. 217, 1681–1689 (1969)
Klevans, L. R., Gebber, G. L.: Facilitatory forebrain influence on cardiac component of baroreceptor reflexes. Amer. J. Physiol. 219, 1235–1241 (1970)
Kobinger, W.: Pharmacologic basis of the cardiovascular actions of clonidine. In: Hypertension: Mechanisms and Management, Eds. G. Onesti, K. E. Kim and J. H. Moyer, pp. 369–380. New York: Grune & Stratton, Inc. 1973
Kobinger, W.: Medicinal chemistry related to the central regulation of blood pressure. II. Pharmacological part. Proc. IV Int. Symp. Med. Chemistry, Main lectures, Edt. J. Maas, pp. 107–120. Amsterdam: Elsevier Scientific Publishing Company 1974
Kobinger, W., Pichler, L.: Evidence for direct α-adrenoceptor stimulation of effector neurons in cardiovascular centers by clonidine. Europ. J. Pharmacol. 27, 151–154 (1974)
Kobinger, W., Walland, A.: Evidence for a central activation of a vagal cardiodepressor reflex by clonidine. Europ. J. Pharmacol. 19, 203–209 (1972a)
Kobinger, W., Walland, A.: Facilitation of vagal reflex bradycardia by an action of clonidine on central α-receptors. Europ. J. Pharmacol. 19, 210–217 (1972b)
Kobinger, W., Walland, A.: Modulating effect of central adrenergic neurones on a vagally mediated cardioinhibitory reflex. Europ. J. Pharmacol. 22, 344–350 (1973)
Korner, P. I., Oliver, J. R., Sleight, P., Chalmers, J. P., Robinson, J. S.: Effects of clonidine on the baroreceptor-heart rate reflex and on single aortic baroreceptor fibre discharge. Europ. J. Pharmacol. 28, 189–198 (1974)
Lisander, B., Martner, J.: Interaction between the fastigial pressor response and the baroreceptor reflex. Acta physiol. scand. 83, 505–514 (1971)
Löfving, B.: Cardiovascular adjustments induced from the rostral cingulate gyrus. With special reference to sympathoinhibitory mechanisms. Acta physiol. scand. 53 (Suppl. 184), 1–81 (1961)
Philippu, A., Demmeler, R., Roensberg, G.: Effects of centrally applied drugs on pressor responses to hypothalamic stimulation. Naunyn-Schmiedeberg's Arch. Pharmacol. 282, 389–400 (1974)
Robson, R. D., Kaplan, H. R.: An involvement of St 155 [2-(2,6-dichlorphenylamino)-2-imidazoline hydrochlorid, Catapres] in cholinergic mechanisms. Europ. J. Pharmacol. 5, 328–337 (1969)
Schmitt, H., Schmitt, H.: Localization of the hypotensive effect of 2-(2,6-dichlorophenylamino)-2-imidazoline hydrochloride (St 155, Catapresan). Europ. J. Pharmacol. 6, 8–12 (1969)
Schmitt, H., Schmitt, H., Fenard, S.: Action of α-adrenergic blocking drugs on the sympathetic centers and their interactions with the central sympatho-inhibitory effect of clonidine. Arzneimittel-Forsch. 23, 40–45 (1973)
Seller, H., Illert, M.: The localization of the first synapse in the carotid sinus baroreceptor reflex pathway and its alternation of the afferent input. Pflügers Arch. ges. Physiol. 306, 1–19 (1969)
Shaw, J., Hunyor, S. N., Korner, P. I.: Sites of central nervous action of clonidin on reflex autonomic function in the unanaesthetized rabbit. Europ. J. Pharmacol. 15, 66–78 (1971)
Struyker-Boudier, H. A. J., van Rossum, J. M.: Clonidine-induced cardiovascular effects after stereotaxic application in the hypothalamus of rats. J. Pharm. Pharmacol. 24, 410–411 (1972)
Walland, A., Kobinger, W., Csongrady, A.: Action of clonidine on baroreceptor reflexes in conscious dogs. Europ. J. Pharmacol. 26, 184–190 (1974)
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Kobinger, W., Pichler, L. Localization in the CNS of adrenoceptors which facilitate a cardioinhibitory reflex. Naunyn-Schmiedeberg's Arch. Pharmacol. 286, 371–377 (1975). https://doi.org/10.1007/BF00506651
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DOI: https://doi.org/10.1007/BF00506651