Response to acetylcholine and nicotine of the perfused vessels of the rabbit ear

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Abstract
1 The vessels of the isolated rabbit ear were perfused at 23 mbar with Krebs solution with (tonic) and without (atonic) noradrenaline (5.9 × 10−7M) at selected temperatures of 20°–38° C. Peripheral resistance units (PRU) were calculated from the observed peak flow rates and alterations caused by drugs expressed as Δ% PRU. 2 ACh is constrictor in the atonic vessel. 3 ACh is a vasodilator of the tonic vessel perfused with NA. This effect is potentiated by anticholinesterase and by denervation, unaffected by botulinum toxin and antagonized by atropine. ACh also dilates the vessel perfused with vasopressin. 4 Increasing the temperature reduces the responses to ACh but increases the effect of anticholinesterase. 5 Nicotine causes a dose dependent dilatation of the tonic vessels, reduced but not abolished by C6, by atropine, by botulinum toxin and by denervation. 6 Nicotine causes a dose dependent constriction of the atonic vessels, abolished by C6 and by phentolamine, reduced by denervation, but unaffected by botulinum toxin.

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