Influence of the dopaminergic agonists bromocriptine, piribedil and nomifensine on the sympathetic neural transmission in the nictitating membrane of the cat.

: The effect of some dopaminergic drugs on the nictitating membrane contractions induced by cervical sympathetic nerve stimulation was investigated in cats. Bromocriptine and piribedil injected into the lingual artery inhibited the nerve stimulation-induced contractions but did not suppress the effect of noradrenaline. Both compounds caused a parallel shift of the frequency-effect curve to the right. Nomifensine (in high doses, after desipramine pretreatment) inhibited the contractions induced both by nerve stimulation and by noradrenaline. Haloperidol or sulpiride antagonized the inhibition due to piribedil. Sulpiride prevented the effect of bromocriptine. We suppose that these agonists have a specific inhibitory activity on the presynaptic dopaminergic receptors.