IS THERE A ROLE OF THE PHOSPHODIESTERASE TYPE 5 (PDE5) IN THE CONTROL OF HUMAN DETRUSOR SMOOTH MUSCLE? A FUNCTIONAL AND MOLECULAR BIOLOGY STUDY

Abstract

INTRODUCTION AND OBJECTIVE: There are hints indicating a signifance of cyclic GMP (cGMP)-mediated mechanisms in the control of human detrusor smooth muscle function. Thus,the use of PDE5 inhibitors to treat the overactive bladder has been suggested. In order to evaluate further the significance of cGMP-PDE isoenzymes in detrusor smooth muscle relaxation, we investigated the effects of selective PDE inhibitors on the tension induced by carbachol and the production of cyclic nucleotides in isolated human detrusor tissue. In addition, the expression of mRNA encoding for PDE isoenzymes 1A, 1B, 1C (cAMP/ cGMP-PDE), 4B, 4D (cAMP-PDE), 5A, 8A and 9A (cGMP-PDE) was evaluated by means of molecular biology (RT-PCR analysis). METHODS: Normal human detrusor tissue was obtained from three male and two female patients who had undergone cystectomy surgery. Using the organ bath technique, the effects of the PDE inhibitors (PDE-I) vinpocetine (Vi, PDE1-I), rolipram (Ro, PDE4-I) sildenafil (Sil), tadalafil (Ta) and vardenafil (Var) (PDE5-Is) (1 nM 10 μM) on the tension induced by the muscarinic agonist carbachol (1 μM) were investigated. The accumulation of cGMP and cAMP in response to drug exposure was determined by means of radioimmunoassays. The expression of mRNA encoding sequences specific for the PDE isoenzymes exmplified above was elucidated using semiquantitative RT-PCR analysis. RESULTS: The tension induced by carbachol was dosedependently reversed by the drugs with the following rank order of efficacy: Var > Sil Ro Vi Tad. Maximum reversion of tension ranged from 34 % (Var) to 7% only (Tad). These effects were paralleled by a 2-fold to 4-fold enhancement in tissue cAMP (control: 8.3 ± 2.9 pmol cAMP/mg protein) and an increase in cGMP which was, however, not significantly different from detrusor strips exposed to either saline or vehicle (control: 0.07 ± 0.045 pmol cGMP/mg protein). RT-PCR revealed different magnitudes of mRNA expression: while there was a predominant relative expression of mRNA encoding for PDE1A, 4B, 4D, 5A, 8A and 9A, only little amounts of PDE1C and 1B mRNA were registered. CONCLUSIONS: Despite the fact that inhibitors of PDE5 exerted only a moderate relaxant response of detrusor strips precontracted by carbachol, our findings indicate that the cGMP pathway might be involved in the control of relaxation of human detrusor smooth muscle. This is supported by the observation that, on the mRNA level, several cGMP-PDE isoenzymes are expressed in the human detrusor.