EFFECT OF 6‐HYDROXYDOPAMINE ON [3H]‐ADENINE NUCLEOTIDE AND [3H]‐NORADRENALINE RELEASE FROM THE GUINEA‐PIG TAENIA CAECUM EVOKED BY ELECTRICAL FIELD STIMULATION, NICOTINE AND PERIVASCULAR NERVE STIMULATION

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Abstract
1 The effects of pretreatment of guinea-pigs with 6-hydroxydopamine (6-OHDA) on the release of [3H]-noradrenaline and [3H]-adenine nucleotide following electrical field, nicotine and perivascular nerve stimulation of guinea-pig taenia caecum were studied. 2 High frequency electrical field stimulation (15,30 Hz) released both [3H]-noradrenaline and [3H]-adenine nucleotide but low frequency (0.5, 5 Hz) stimulation, producing comparable muscle relaxation led only to [3H]-noradrenaline release. 3 6-OHDA (50–200 mg/kg) pretreatment inhibited the muscle relaxation and, [3H]-noradrenaline release with electrical stimulation or with nicotine in isolated taenia but did not affect the release of [3H]-nucleotide. 4 A low dose of 6-OHDA (50 mg/kg), completely inhibited the muscle relaxation and [3H]-noradrenaline release elicited by perivascular nerve stimulation. 5 Both tissue noradrenaline content and [3H]-noradrenaline uptake were decreased to the same extent by low as well as high doses of 6-OHDA: noradrenaline content was reduced to 20% and uptake to 30% of the control value. 6 Catecholamine fluorescence disappeared from tissue layers of the taenia after treatment with a high dose of 6-OHDA. 7 In these experiments the inhibitory action of electrical stimulation and nicotine on the taenia can be correlated better with noradrenaline than with nucleotide release.

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