TY - JOUR T1 - Identification, localization and functional analysis of imidazoline and alpha adrenergic receptors in canine prostate. JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 1063 LP - 1071 VL - 268 IS - 2 AU - D Felsen AU - P Ernsberger AU - P M Sutaria AU - R J Nejat AU - P Nguyen AU - M May AU - D S Breslin AU - D N Marion AU - E D Vaughan, Jr Y1 - 1994/02/01 UR - http://jpet.aspetjournals.org/content/268/2/1063.abstract N2 - In nonsurgical management of benign prostatic hyperplasia, drugs which interfere with prostate contraction mediated through the alpha-1 adrenergic receptor are used. Clonidine acts at alpha adrenergic and I1-imidazoline receptors. In the present study, we found the Kd for [3H]clonidine binding to I1 sites in canine prostate to be 4 +/- 1 nM; the Bmax was 18 +/- 2 fmol/mg of protein. Inhibition of binding by imidazolines and by brain extracts containing putative endogenous ligand confirmed the identity of these sites as I1-imidazoline. Autoradiographic studies showed localization of both I1 and alpha-2 sites to the glandular epithelium. We sought to determine whether in vivo activation of the I1-imidazoline sites by clonidine mediates its contractile action in canine prostate. Dose-response curves were generated for para-aminoclonidine in the presence of vehicle alone, yohimbine (alpha-2 antagonist), idazoxan (alpha-2/I1/I2 antagonist) and prazosin (alpha-1 antagonist). Prazosin was the most effective antagonist. Yohimbine was less effective and did not effectively discriminate between para-aminoclonidine and phenylephrine, an alpha-1-selective agonist. Idazoxan antagonized para-aminoclonidine, but by not more than 50% at any dose. These results suggest that clonidine is active primarily at alpha-1 receptors on prostate smooth muscle in vivo. Thus the function of the I1 and alpha-2 receptors in the prostate remains to be determined; however, they may be involved in epithelial cell function. ER -