Presence of D1 receptors in the rabbit carotid body

Rabbit carotid bodies incubated in vitro in the presence of 5 x 10(-4) M 3-isobutyl 1-methylxanthine have cyclic AMP levels of 13.1 +/- 1.6 pmol/mg fresh tissue (means +/- S.E.M; n = 11). Dopamine (10(-6) and 10(-5) M) increased the cyclic AMP content to 24.4 +/- 2.85 and 40.6 +/- 3.29 pmol/mg tissue. The specific D1 agonist SKF38393 at 10(-6) M increased the cyclic AMP content to 23.9 +/- 2.3 pmol/mg fresh tissue and the specific D1 antagonist SCH23390 at 10(-6) M completely blocked the effect of 10(-5) M dopamine. dBcAMP (2 x 10(-3) M) potentiated the release of dopamine induced by a mild hypoxic stimulus and SKF38393 did not modify it. It is concluded that the carotid body has D1 receptors positively coupled to adenylate cyclase that seem to be located in the vasculature of the organ. This set of receptors, when activated by injected dopamine, produced vasodilatation leading to a decrease in carotid sinus nerve activity.