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. 1983 Jan;78(1):247–253. doi: 10.1111/j.1476-5381.1983.tb09386.x

The effects of yohimbine on presynaptic and postsynaptic events during sympathetic nerve activation in cattle iris: a critique of presynaptic receptor theory.

S Kalsner
PMCID: PMC2044802  PMID: 6130810

Abstract

1 The effects of presynaptic alpha-adrenoceptor blockade on both the efflux of 3H-transmitter and on the magnitude of the effector response were measured simultaneously in a smooth muscle preparation which responds to field stimulation with noradrenergic beta-receptor-mediated relaxation. 2 In the presence of atropine, the circular muscle of cattle iris relaxes in response to noradrenaline and to field stimulation at 2 Hz with 10, 20, 50 and 100 pulses. 3 Yohimbine (3 x 10(-6) M), a potent presynaptic alpha-adrenoceptor antagonist, increased the stimulation-induced efflux of tritium to about 2.0 times control values and, contrary to theory, did so to a similar extent regardless of pulse number and with apparent indifference to the synaptic concentration of transmitter, as confirmed by the varying size of the postsynaptic response. 4 In most cases, yohimbine had no significant effect on the magnitude of the relaxations to nerve stimulation. 5 It is concluded that negative feedback regulation of transmitter release, if it functions at all, and this itself seems doubtful, would not have a substantial impact on the size of the effector response.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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