Dopaminergic inhibition of sympathetic activity in the cat.

The influence of dopaminergic agonists on the spontaneous and evoked activity of the sympathetic postganglionic renal efferent fibres was studied in lightly anaesthetized cats (urethane, 600 mg/kg, ip). Apomorphine, bromocriptine and piribedil (0.2, 0.07 and 0.4 mg/kg iv, respectively) depressed the spontaneous activity of the renal nerve. Electrical stimulation (16 V, 0.3 ms, 2-128 Hz, 2 s) of the sciatic nerve elicited a burst of activity of the sympathetic efferents followed by a silent period. Apomorphine and piribedil (the same doses as above) prolonged the duration of the silent periods. All these effects of dopaminergic agonists were antagonized by haloperidol (0.05-0.1 mg/kg iv). The results suggest that administration of dopaminergic agonists leads to preponderance of inhibition in the somato-sympathetic reflex integration.