Dopamine (DA) release (r) from the carotid body (CB) is thought to be modulated by feedback inhibition mediated by DA D2 autoreceptors. We tested the hypothesis that CB DAr is autoregulated in a concentration and age dependent manner. Using an in vitro CB infusion model [Bairam, A., Marchal. F., Cottet-Emard, J.M., Basson, H., Pequignot, J.M., Hascoet, J.M., Lahiri, S., 1996b. Effects of hypoxia on carotid body dopamine content and release in developing rabbits. J. Appl. Physiol. 80, 20-24.], we evaluated under unstimulated conditions the effects of 0.001, 0.01, 0.1, 1.0 and 10.0 microM of the specific DA D2 receptor antagonist domperidone on CB DAr in adult rabbits. In 10-day-old rabbit pups, concentrations of 0.01, 0.1, 1.0 microM were studied. In adult CBs, domperidone increased DAr in a concentration-dependent manner. DAr (pmol/h) was significantly greater compared to control (without domperidone) starting at a domperidone concentration of 0.1 microM (P<0.01). In 10-day-old pup CBs, 1.0 microM domperidone was required to produce a significant increase of DAr (pmol/h) compared to control (P<0.005). However, control DAr (as % of total catecholamine) was about 40%; significantly higher than 24% observed in adult CBs (P<0.001). We conclude that in rabbit CB, DAr is controlled by an autoreceptor mechanism in a concentration-dependent manner and this mechanism is less developed in pups than in adults.