Naunyn-Schmiedeberg's Archives of Pharmacology

, Volume 330, Issue 3, pp 163–168 | Cite as

An analysis of theα-adrenoceptor modulation of vasomotor tone at the level of lateral medullary pressor area (LMPA)

  • J. N. Sinha
  • S. Gurtu
  • D. K. Sharma
  • K. P. Bhargava


Microinjection of noradrenaline and clonidine into lateral medullary pressor area (LMPA) of chloralose anaesthetized cats produced dose dependent decrease in blood pressure without affecting heart rate, while phenylephrine did not elicit any cardiovascular response. Selectiveα2-adrenoceptor, antagonists idazoxan and piperoxan, microinjected locally, blocked the effects of the agonists but prazosin and phenoxybenzamine, which are relatively selective forα1-adrenoceptors, failed to do so. Clonidine did not elicit any response in guanethidine pretreated cats but noradrenaline microinjected into LMPA of these animals induced a pressor response which was blocked by prazosin pretreatment. It is concluded that catecholaminergic fibres impinging upon this are inhibit the activity of the inhibitory second order baroreceptor neurone by activatingα1-adrenoceptors whileα2-adrenoceptors situated presynaptically on these inhibitory catecholaminergic nerve terminals are responsible for the manifestation of the hypotensive effect of clonidine and exogenously administered noradrenaline.

Key words

α-Adrenoceptors Baroreflex Clonidine Noradrenaline Sympathetic tone 


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Copyright information

© Springer-Verlag 1985

Authors and Affiliations

  • J. N. Sinha
    • 1
  • S. Gurtu
    • 1
  • D. K. Sharma
    • 1
  • K. P. Bhargava
    • 1
  1. 1.Department of Pharmacology and TherapeuticsKing George's Medical CollegeLucknowIndia

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