Dopamine type 2 receptor expression and function in rodent sensory neurons projecting to the airways.

Agonists of the dopamine receptors have been demonstrated to have bronchodilatory properties in pathologically constricted airways. The mechanism by which these agonists induce bronchodilatation is thought to involve airway sensory nerves. In this study, the expression and function of dopamine D(2) receptor were examined in sensory ganglia supplying the airways. Neuronal dopamine D(2) receptor mRNA expression was demonstrated by single-cell RT-PCR following laser-assisted microdissection. The projection of the neurons to the airways was confirmed by retrograde neuronal labeling. In functional studies, dopamine D(2) receptor agonists (AR-C65116AB and ropinirole) inhibited intraneuronal calcium mobilization in rat capsaicin-sensitive primary sensory neurons and capsaicin-induced plasma extravasation in the rat trachea. Our results provide support to the hypothesis that dopamine D(2) receptor activation inhibits neurogenic inflammation and proinflammatory reflex responses.

Bradykinin B2 receptors mediate contraction in the normal and inflamed human gallbladder in vitro.

BACKGROUND & AIMS: The components of the kinin system, including kinongens, kininogenases, and B(2) and B(1) receptors, are expressed and activated during inflammation. Here, we investigated the expression of the kinin B(2) receptor messenger RNA, kininogen and kallikrein immunoreactivity, and the ability of kinins to contract control and inflamed gallbladders in vitro. METHODS: Human gallbladders, obtained from patients undergoing cholecystectomy either for acute cholecystitis secondary to gallstone disease or during elective gastro-entero-pancreatic surgery (controls), were processed for reverse-transcription polymerase chain reaction analysis, kallikrein and kininogen immunohistochemistry, binding studies, and in vitro contractility studies. RESULTS: Tissue expression of B(2) receptor messenger RNA and specific binding of [(3)H]-bradykinin increased significantly in acute cholecystitis compared to controls. Kallikrein immunoreactivity was detected in the epithelium and infiltrating leukocytes, whereas kininogen immunoreactivity in the lumen of blood vessels and interstitial space. Bradykinin contracted isolated strips of control and acute cholecystitis gallbladders. In acute cholecystitis tissue, efficacy of bradykinin was higher than that of control gallbladders and similar to that of cholecystokinin. The contraction induced by bradykinin was significantly attenuated by B(2) receptor antagonism but not by cyclooxygenase inhibition and B(1), muscarinic, or tachykinin receptor antagonism. CONCLUSIONS: All the components of the kinin system are expressed in the human gallbladder. Bradykinin is a powerful spasmogen via B(2) receptor activation in the normal and, especially, in the inflamed human gallbladder.