Relaxation induced by milrinone and rolipram in human penile arteries and veins

PDE4 and PDE5 regulate cyclic nucleotides relaxing effects in human umbilical arteries

Cyclic nucleotides (cAMP and cGMP) are the main second messengers linked to vasodilatation. They are synthesized by cyclases and degraded by different types of phosphodiesterases (PDE). The effect of PDE inhibition and cyclases stimulation on 5-hydroxytryptamine (5-HT; 1 microM) and histamine (10 microM) contracted arteries was analysed. Stimulation of guanylate cyclase or adenylate cyclase relaxed the histamine- and 5-HT-induced contractions indicating that intracellular increase of cyclic nucleotides leads to vasodilatation of the human umbilical artery. We investigated the role of different PDE families in the regulation of this effect. The presence of the different PDE types in human umbilical artery smooth muscle was analysed by RT-PCR and the expression of PDE1B, PDE3A, PDE3B, PDE4C, PDE4D and PDE5A was detected. The unspecific PDE inhibitor 3-isobutyl-1-methylxanthine (IBMX; 50 microM) relaxed histamine-contracted human umbilical artery on 47.4+/-7.2%. This effect seems to be due to PDE4 and PDE5 inhibition because among the selective PDE inhibitors used only the PDE4 inhibitor (rolipram; 1 microM) and the PDE5 inhibitors (dipyridamole and T0156; 3 microM and 1 microM respectively) induced significant relaxation (39.0+/-8.7, 30.4+/-6.0 and 36.3+/-2.8 respectively). IBMX, dipyridamole and T0156 produced similar relaxation on 5-HT-induced contraction. After forskolin, the addition of IBMX or rolipram increased the effect of the adenylate cyclase stimulator and almost completely relaxed the human umbilical artery contracted by histamine (92.5+/-4.9 and 90.9+/-4.7 respectively), suggesting a main role of PDE4. The data obtained with 5-HT contracted arteries confirmed this, because only rolipram and IBMX significantly increased the forskolin vasodilator effect. The administration of dipyridamole and T0156 after sodium nitroprusside (SNP) induced a significant increase of the SNP relaxant effect on histamine-contracted arteries, but PDE1 and PDE3 inhibition did not increase the effect of the guanylate cyclase stimulator. Similar effects were obtained in 5-HT contracted arteries, the SNP induced relaxation was increased by the PDE5 inhibition, but not by PDE1 or PDE3 inhibition. In summary, our results demonstrate that: 1) the increase of cAMP and/or cGMP levels induces relaxation of the human umbilical vascular smooth muscle; 2) four families of PDE are expressed in this smooth muscle: PDE1, PDE3, PDE4 and PDE5; 3) between these families, PDE4 and PDE5 are the key enzymes involved in the regulation of the relaxation associated to cAMP and cGMP, respectively.

Effect of Sildenafil and Rolipram on Adrenergic Responses in Isolated Human and Monkey Corpus Cavernosum

OBJECTIVE

Evaluate and compare effects of phosphodiesterase inhibitors (PDEIs), sildenafil and rolipram, on adrenergic contractile responses of human and monkey cavernosal smooth muscle.

METHODS

Human penises were obtained from patients undergoing gender reassignment surgery. Isolated human and monkey corpus cavernosum (CC) strips were suspended in tissue bath chambers for isometric tension experiments. The effects of the drugs on precontracted monkey and human CC and neurogenic contractions in human CC were investigated.

RESULTS

Both sildenafil and rolipram induced concentration-dependent relaxations of human and monkey CC strips precontracted with noradrenaline (NA). The IC(50) values, determined by reverse regression for nitroglycerin (NTG), isoprenaline, and sildenafil in monkey CC, were, respectively, 1.5+/-0.9x10(-7) M, 3.7+/-0.6x10(-6) M, and 1.7+/-0.7x10(-5) M. Similarly, in human CC muscle, sildenafil was weaker than NTG as a muscle relaxant. Sildenafil, 1.5 microM, reduced neurogenic contractions in human CC due to stimulation of predominantly adrenergic nerves. The suppressant effect of sildenafil on adrenergic transmission was attenuated in CC strips pretreated with N omega-nitro-L-arginine and overcome with a higher stimulus frequency or tetraethylammonium. Rolipram partially inhibited adrenergic excitatory response but without significantly affecting NA-induced contraction.

CONCLUSIONS

Sildenafil and rolipram induced concentration-dependent reversal of human and monkey CC tone mediated by NA. Both PDEIs attenuated contractile adrenergic response of human CC to electrical stimulation. The results also underline the importance of the cyclic adenosine monophosphate-dependent signalling pathway in regulating the tone. PDE4 inhibition in CC is an additional mechanism for erection and potential therapeutic adjunct.

REVIEW: Review of Phosphodiesterases in the Urogenital System: New Directions for Therapeutic Intervention

INTRODUCTION

With the success of Phosphodiesterase (PDE) type 5 inhibitors (i.e., sildenafil, tadalafil, vardenafil) in the treatment of erectile dysfunction (ED), PDEs are considered attractive targets for drug intervention in the urogenital tract.

AIM

To review the role of PDEs, which exist as a superfamily of enzymes comprising 11 distinct families, in the urogenital system, focusing on anatomical locations, functions and dysfunctions, potential disorders that could be treated, and any promising new selective PDE inhibitors under development.

METHODS

Included are (i) abstracts from 2001, 2002, and 2003; (ii) a MEDLINE search from 1996 through December 2003; and (iii) a pipeline search for therapeutics in development. Data from animal experiments are presented when there is a paucity of human data, but with the caveat that the distribution of PDE isozymes in a specific tissue can vary between species.

RESULTS

PDE mRNA and protein have been localized throughout the normal human urogenital tract. Double-blind, placebo-controlled studies suggest possible new clinical roles for sildenafil, including prophylaxis to preserve penile smooth muscle and erectile function after radical prostatectomy, and treatment of ejaculatory delay secondary to serotonergic reuptake inhibitor antidepressant therapy. Open-label studies suggest a potential clinical role for: vinpocetine (a PDE1 inhibitor) in the treatment of incontinence and low-compliance bladder; and sildenafil in the treatment of premature ejaculation, prostate-related lower urinary tract symptoms, and in women who have had unsuccessful in vitro fertilization. Several new orally administered PDE5 inhibitors are in early clinical development for the treatment of ED. Potential indications for PDE inhibitors that are suggested by preclinical data include Peyronie's disease, ureteral colic, male and female birth control, and prevention of preterm labor.

CONCLUSIONS

Drug selectivity and differential PDE tissue distribution allow for potential targeted intervention for numerous disorders related to the urogenital tract.