ABSTRACT
Results from experimental studies suggested a significance of the nitric oxide (NO)-cGMP- and cAMP-pathways in the control of the function of the smooth musculature of the human prostate. In addition, it has also been assumed that the vasoconstrictory peptide endothelin-1(ET-1) may play a role in the dynamic component of benign prostatic hyperplasia (BPH) and the so-called lower urinary tract symptomatology (LUTS). Nevertheless, up till now, little is known as to potential interactions between the contraction of prostatic smooth muscle mediated by ET-1 and the relaxation induced by NO and cGMP. Thus, it was the aim of the study to elucidate the effects of drugs interfering with the cGMP-pathway on the tension induced by ET-1 of isolated human prostate tissue, as well as contractile responses of isolated strip preparations to ET-1 and angiotensin-II (AT-II). Macroscopically normal human prostate tissue from the transition zone was obtained from male patients who had undergone surgery for localized cancer of the prostate or urinary bladder. Using the organ bath technique, the ability of ET-1 and AT-II to contract isolated prostate strips was evaluated. In another set-up, the effects of the NO-donor S-nitrosogluthatione (GSNO) and C-type natriuretic peptide(CNP), known as an endogenous ligand of the membrane bound guanylyl cyclase, (1 nM-1/10 microM) on the tension induced by 0.1 microM ET-1 of human prostate strips were investigated. The adenylyl cyclase stimulating agents forskolin and NO-donor natrium nitroprusside (NNP) were used as reference compounds. While AT-II failed to contract the prostate tissue, ET-1 induced stable and reproducible contractions of the tissue strips. The tension induced by 0.1 microM ET-1 was dose-dependently reversed by the drugs. The rank order of efficacy was forskolin >NNP>CNP(1 microM)>GSNO. R(max) values ranged from 55% (forskolin) to 35% (GSNO). Forskolin was the only compound which reached an EC50 value. Our results demonstrate that drugs in terfering with the cGMP- and cAMP-pathways can reverse the tension induced by ET-1. These findings are in support of the hypothesis that both cGMP and cAMP contribute to the control of the prostate smooth muscle tension and may provide new strategies for the future pharmacotherapy of LUTS und BPH.