Mepartricin long-term administration indirectly regulates steroid hormone and adrenergic receptor concentrations in the prostate of aged rats

Mepartricin is a semi-synthetic macrolide antibiotic developed as a drug for the treatment of benign prostatic hyperplasia (BPH) in human patients. In the present study, aged rats are used as an experimental model to evaluate the effects of mepartricin on circulating hormone concentrations and prostate receptor concentrations, to compare these possible effects with clinical findings observed in long-term treated dogs. Fifty-six aged male rats were randomly divided into four experimental groups treated orally with 0 (group 1), 2 mg (group 2), 5 mg (group 3) and 20 mg (group 4) mepartricin/kg of body weight. for 28 days respectively. Serum oestradiol and testosterone concentrations were measured by radio-immune-assays methods. Binding assays were used to measure the prostate concentrations of oestrogen receptors (ER), androgen receptors (AnR), a1-adrenergic receptor (a1-AR), and b-adrenerergic receptor (b-AR) subtypes. Mepartricin induced a significant reduction of prostate weight and serum oestradiol concentrations. Serum testosterone concentrations were unaffected. The treatment induced a significant down-regulation of ER concentrations (P < 0.05) and a significant up-regulation of AnR (P < 0.05) in rat prostate. Mepartricin induced a significant (P < 0.05) dose-dependent up-regulation of a1-AR and b2-AR. In contrast, the concentration of b3-ARs was significantly decreased (P < 0.05) in treated animals. The increase in prostate b2-AR concentrations observed in subjects treated with mepartricin may be a favourable element in the evolution of BPH, because of the role exerted by these receptors in the control of prostatic smooth muscle relaxation. Curiously, b3-AR concentrations were significantly reduced in treated animals. Data collected suggest that the prostatic b-AR expression might be strongly influenced by oestrogen deprivation (mepartricin treatment); therefore, the combination of oestrogen suppression (mepartricin) and adrenergic suppression (a1-AR blockers) may be proposed as a possible nonhormonal therapeutic strategy for the treatment of benign prostatic hyperplasia in dogs.