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  • Title: Indications for vascular alpha- and beta-2 adrenoceptors in synapses of the muscarinic pathway in the pithed normotensive rat.
    Author: Wilffert B, Gouw MA, De Jonge A, Timmermans PB, van Zwieten PA.
    Journal: J Pharmacol Exp Ther; 1982 Oct; 223(1):219-23. PubMed ID: 6288920.
    Abstract:
    In the pithed normotensive rat the adrenoceptors involved in the hypertensive and tachycardic effects of the indirectly acting sympathomimetic agent tyramine and of electrical stimulation of the spinal cord (TH5-L4 or C7-Th1) were analyzed. The tools used for the identification of the adrenoceptors were the selective alpha-1 adrenoceptor blocking drug prazosin, the selective alpha-2 adrenoceptor antagonist rauwolscine, the beta-1 blocker atenolol and the selective beta-2 adrenoceptor blocking agent ICI 118,551. The participation of vascular alpha-2 adrenoceptors in the pressor response of tyramine was shown. The increase in blood pressure induced by electrical stimulation of the spinal cord (TH5-L4) was used to demonstrate that alpha-2 adrenoceptors were activated via ganglionic muscarinic receptors. The tachycardia evoked by electrical stimulation of the spinal cord (C7-Th1) was not influenced by beta-2 adrenoceptor blockade. It was enhanced, however, by the alpha-2 adrenoceptor antagonist rauwolscine. It is hypothesized that activation of ganglionic nicotinic receptors leads to stimulation of the nearest varicosities interfering with alpha-1 adrenoceptors. However, activation of ganglionic muscarinic receptors may lead to an additional release of neurotransmitter in the more distant varicosities endowed with alpha-2 or beta-2 adrenoceptors.
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