Effects of dopamine on carotid chemo- and baroreceptors in vitro.

1. The effects of dopamine on the sensory discharges originating from arterial chemo- and baroreceptors were studied in vitro using carotid bodies or sinuses excised from anaesthetized cats and superfused with Locke's solution. 2. Intrastream injections of dopamine 10-200 mug produced a transient depression of the frequency of chemoreceptor discharges. This effect was observed in response to the first injection in eighteen out of twenty preparations. 3. The inhibitory effect of dopamine can counteract partially or totally the excitation of chemoreceptors evoked by simultaneous application of acetylcholine or cyanide. 4. This inhibitory effect of dopamine is reduced or abolished by pretreatment with dopaminergic (Spiroperidol) or alpha-adrenergic (Dibenamine) blockers. 5. In response to repeated injections of dopamine applied at short intervals, the inhibitory effect is replaced by a biphasic effect (early inhibition followed by late excitation), a late and long-lasting excitation or no changes in chemoreceptor activity. The late excitatory effects of dopamine are not blocked by dopaminergic or alpha-adrenergic blockers. 6. Noradrenaline does not affect the chemoreceptor activity of the superfused carotid body. DL-DOPA induces only a late and long-lasting excitatory effect. 7. In carotid sinus preparations, dopamine induces a weak but long-lasting increase in the frequency of baroreceptor discharges. 8. It is concluded that dopamine may play a modulatory role in the generation of chemoreceptor activity through local regulatory processes.