Elsevier

Peptides

Volume 18, Issue 10, 1997, Pages 1603-1608
Peptides

Article
Binding 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

https://doi.org/10.1016/S0196-9781(97)00247-7Get rights and content

Abstract

Bhargava, H. N., V. M. Villar, J. Cortijo and E. J. Morcillo. Binding 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. Peptides 18(10) 1603–1608, 1997.—The role of endogenous opioid peptides in the regulation of bronchomotor tone, as well as in the pathophysiology of asthma is uncertain. We have studied the binding of highly selective [3H]labeled ligands of μ-([D-Ala2, MePhe4, Gly-ol5]enkephalin; DAMGO), δ ([D-Pen2, D-Pen5]enkephalin; DPDPE), and κ-(U-69,593) opioid receptors to membranes of trachea, main bronchus, lung parenchyma and pulmonary artery obtained from normal (unsensitized) and actively IgE-sensitized rats acutely challenged with the specific antigen. [3H]DAMGO, [3H]DPDPE and [3H]U-69,593 bound to membranes of normal and sensitized tissues at a saturable, single high-affinity site. The rank order of receptor densities in normal tissues was δ- ≥ κ- ≥ μ-, with lung parenchyma exhibiting the greatest binding capacity for δ- and μ- receptors compared to the other regions examined. The Kd values showed small differences between ligands and regions tested. The μ- and δ-opioid receptor densities were decreased in sensitized main bronchus and lung parenchyma, respectively, compared to normal tissues. By contrast, κ-opioid receptor density was augmented in sensitized lung parenchyma but an increase in Kd values was also observed. These differential changes in the density and affinity of opioid receptor types may be related to alterations in endogenous opioid peptides during the process of sensitization.

Section snippets

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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