ArticleBinding of [3H][D-Ala2, MePhe4, Gly-ol5] Enkephalin, [3H][D-Pen2, D-Pen5]Enkephalin, and [3H]U-69,593 to Airway and Pulmonary Tissues of Normal and Sensitized Rats☆
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Animals
Adult male specific-pathogen-free Sprague–Dawley (Sasco King Animal Co., Madison, WI) rats weighing 225–250 g were housed in a room with controlled temperature (23 ± 1°C), humidity (50 ± 10%) and a 12 h dark-light cycle (light 0600–1800 h) for at least 4 days before being used. Food and water were available ad libitum.
Chemicals
The radioligand [3H]DAMGO (specific activity 21.86 Ci/mmol) and unlabeled DPDPE and U-69,593 were obtained from the Research Technology Branch, National Institute on Drug Abuse
Results
The binding of [3H]DAMGO (0.92 nM), [3H]DPDPE (3 nM), and [3H]U-69,593 (0.45 nM) to membranes of trachea, main bronchus, lung parenchyma and pulmonary artery obtained from normal and sensitized rats is shown in Table 1. In general, the binding of [3H]DPDPE to each of these regions was significantly higher than the binding of [3H]DAMGO and [3H]U-69,593 to the same respective regions. For [3H]DPDPE and [3H]U-69,593, but not for [3H]DAMGO, the binding in lung parenchyma was significantly higher
Discussion
The results from the first part of the present study demonstrate the presence of specific membrane receptors for the μ-, δ-, and κ-opioid agonists in conducting airways (trachea and main bronchus), lung parenchyma and pulmonary artery obtained from normal (i.e., unsensitized) rats. Using highly selective [3H]labeled ligands of these opioid receptor types such as DAMGO (μ-agonist), DPDPE (δ-agonist), and U-69,593 (κ-agonist) we found the binding to be saturable, and the Scatchard analysis of the
Acknowledgements
The radioligand [3H]DAMGO, unlabeled U-69,593 and unlabeled DPDPE were obtained from the Research Technology Branch, National Institute on Drug Abuse (Rockville, MD) through the courtesy of Mr. Kevin Gormley. The authors thank Ms. Celina Tejada for excellent secretarial assistance.
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This study was supported by a Research Scientist Development Award K02-DA-00130 from the National Institute of Drug Abuse. Dr. V. Villar is the recipient of a re-incorporation contract from the Ministry of Education and the University of Valencia, Spain.