Identification and distribution of peripheral benzodiazepine binding sites in male rat genital tract

In the present study we identified and characterized the distribution of high-affinity peripheral benzodiazepine binding sites (PBzS) in male rat vas deferens (whole, and prostatic and epididymal portions), prostate, seminal vesicles, and Cowper's glands. [3H]PK 11195, an isoquinoline carboxamide derivative, was used as a radioligand specific for PBzS. Scatchard analysis of saturation curves of [3H]PK 11195 binding in the whole vas deferens, the prostatic and epididymal portions of the vas deferens, the prostate, the seminal vesicles, and Cowper's glands yielded mean maximal numbers of binding sites of 1211 +/- 158, 1012 +/- 311, 1451 +/- 156, 1805 +/- 86, 865 +/- 51, and 2251 +/- 135 fmol/mg protein, respectively. The equilibrium dissociation constant values ranged between 1 and 3 mM in all the above tissues. The ability of various drugs to displace the specific binding of [3H]PK 11195 from PBzS in Cowper's gland membranes was also tested. The inhibition constants for Ro 5-4864, diazepam, and PK 11195 were 28, 330, and 4 nM, respectively, whereas clonazepam, Ro 15-1788, and testosterone were inefficient in displacing [3H]PK 11195. The presence of high densities of PBzS in the male genital tract suggests a functional role in these hormone-dependent organs.