Abstract
1 In the isolated vas deferens of the guinea-pig, contractile responses to adrenergic nerve stimulation at 2 Hz were depressed by exogenous dopamine (5 microM) and this effect was abolished in the presence of phentolamine (0.3 microM), suggesting that it was due to an agonist action of dopamine on alpha-adrenotors. 2 The depression by dopamine (5 microM) of contractile responses to nerve stimulation was correlated with reduction in amplitude of single excitatory junction potentials (e.j.ps) evoked by nerve stimulation, but not with depression of spontaneous junction potentials. 3 By contrast, during repetitive nerve stimulation at 1 Hz the depressant effect of dopamine on e.j.p. amplitude became less pronounced, due to the amount of facilitation being greater than that occurring under control conditions in the same cell. 4 The alpha-adrenoceptor antagonist, phentolamine (10 microM), also increased the amount of facilitation during repetitive nerve stimulation. 5 In the presence of phentolamine (10 microM), the depressant effect of dopamine (5 microM) on single e.j.ps was abolished but its enhancing effect on facilitation was not reduced. 6 It is suggested that the enhancement of facilitation during repetitive stimulation by both dopamine and phentolamine is independent of their actions on presynaptic alpha-adrenoceptors.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
