Impact of phosphodiesterase (PDE) isoenzymes in the control of the human detrusor
Wednesday, 28 October 2009- There are hints from basic research studies indicating a significance of cyclic GMP (cGMP)-mediated mechanisms in the control of human detrusor smooth muscle. Thus, recently, the use of PDE5 inhibitors to treat the overactive bladder has been suggested (J. Urol. 178: 2040– 2043, 2007).
In order to evaluate further the significance of cGMP-phosphodiesterase (PDE) isoenzymes in detrusor smooth muscle relaxation, German researchers investigated the effects of selective PDE inhibitors on the tension induced by carbachol and the production of cyclic nucleotides in isolated human detrusor tissue.
Stefan Ückert and colleagues presented their findings and won the first prize for best abstract from Karl Storz at the recent EAU 9th Central European Meeting held in Ljubljana, Slovenia.
In addition, the researchers also evaluated the expression of messenger ribonucleic acid (mRNA) encoding for PDE isoenzymes 1A, 1B, 1C (cAMP/cGMP-PDE), 4B, 4D (cAMP-PDE), 5A, 8A and 9A (cGMP-PDE) by means of molecular biology (RT-PCR analysis).
Human detrusor tissue, excised from the dome and lateral walls, 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) (1nM–10 mM) on the tension induced by the muscarinic agonist carbachol (1 mM) 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 RT-PCR analysis. Human penile corpus cavernosum (HCC) was used as a reference tissue.
The results showed that the tension induced by carbachol was dose dependently 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).
Only sildenafil induced a linear increase in the accumulation of intracellular cGMP, however, this enhancement was 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. The expression of mRNA encoding for PDE5 was higher in the HCC than in the detrusor.
"Despite the fact that inhibitors of PDE5 exerted only a moderate relaxant response on detrusor strips precontracted by carbachol, our findings indicate that the cGMP pathway might be involved in the control of relaxation and contraction of human detrusor smooth muscle," the investigators concluded. "This is supported by the observation that, on the mRNA level, several cGMP-PDE isoenzymes are expressed in human detrusor smooth muscle."
Source: S. Ückert, P. Sandner, et al., "Investigating the significance of phosphodiesterase (PDE) isoenzymes in the control of the human detrusor – a functional and molecular biology approach," First Prize for Best Abstract, Karl Storz, EAU 9th Central European Meeting, Ljubljana, Slovenia, October 23 to 24, 2009.
