Abstract

CABEZAS, Gloria A  and  VELASCO, Manuel. Modulación dopaminergica mediada por receptores DA1, en tráquea aislada de rata. AVFT [online]. 2006, vol.25, n.2, pp.67-71. ISSN 0798-0264.

We have previously demonstrated that low doses of inhaled dopamine (0.5-2 µg/ml/min) induces bronchial dilatation in patients with acute asthma attack, suggesting that dopamine effect is mediated by dopaminergic receptors rather than by adrenergic receptors. In the present work we examined the probable dopaminergic regulatory effect on rat tracheal smooth muscle and the β₂, α₁, α₂ adrenergic and, DA₁, and DA₂ dopaminergic antagonist effect. We studied 90 male Sprague Dawley rats weighing 200 - 400 grams. Tracheal rings were excised and placed in an organ bath containing Krebs´s solution at 37ºC, gassed with oxygen (95%) and carbon dioxide (5%). Contractile responses were recorded with an isometric transducer in a polygraph (Letica, Spain). Contraction was induced by adding acetylcholine, into the bath. Dopamine doses response curves were obtained. Dopamine (0.1, 0.3, µM) transiently increased cholinergic contractions at first, followed by a marked inhibition; adding dopamine (10 µM) completely reversed contraction. Biphasic dopaminergic response was not blocked by β₂ adrenergic antagonists propranolol (0.1µM) or by antagonists α₁, terazosin (0.1µM) or α₂ yohimbine (0.1µM) administration 15 minutes before contractions were elicited. DA₂ antagonist metoclopramide (1, 2, 4, 8 µM) increased cholinergic contraction and did not block dopamine induced bronchodiltation. DA1 antagonist SCH23390 (0.1µM), elicited an abrupt and prolonged contraction (more than 15 min.) and partially inhibited the inhibitory effect of dopamine. We concluded that on airways a) dopamine effect is mediated by DA₁ rather than by DA₂ receptors; b) adrenergic receptors are not involved on dopamine induced response; c) metoclopramide seems to exhibit a cholinergic effect. d) In addition to DA₁ antagonist SCH23390 has intrinsic contractile activity on airway smooth muscle that deserves further research.

Keywords : bronchial dopaminergic receptors; dopaminergic bronchial dilatation; nervous control of airways; bronchial asma.