Extraction of active clonidine-displacing substance from bovine lung and comparison with clonidine-displacing substance extracted from other tissues

Crude methanolic clonidine-displacing substance (CDS) extracted from bovine lung competed for radioligand binding from alpha(2)-adrenoceptors and I-2- sites present in rat brain membranes, and from I-1-sites present in rat bra in and kidney membranes. There was no difference in the competition of [H-3 ]clonidine binding to alpha(2)-adrenoceptors present in either rat or rabbi t brain membranes by the crude CDS extract and therefore either tissue coul d be used to estimate the number of units of CDS present in extracts. Furth er purification by reverse phase high performance liquid chromatography (RP -HPLC), with UV detection, of extracts obtained from bovine lung, brain and rat brain exhibited similar three-peak profiles, previously reported. Corr esponding fractions competed for radioligand binding to alpha(2)-adrenocept ors present in rat brain membranes, eluting between 19 and 23 min, which co rresponded with the middle peak of the three-peaks. Therefore, we propose t he CDS-like material eluting from all these tissues to be similar. Interest ingly, CDS extracted from bovine adrenal glands under the same conditions s howed a similar three-peak profile, but did not repeat the displacement of binding just at 19-23 min, but at every time point after 4 min. This sugges ts this tissue could represent a source of CDS in this species. (C) 1999 El sevier Science B.V. All rights reserved.