Effect of sildenafil on renin secretion in human subjects

Regulation of the renin-angiotensin-aldosterone system by cyclic nucleotides and phosphodiesterases

The renin-angiotensin-aldosterone system (RAAS) is one of the key players in the regulation of blood volume and blood pressure. Dysfunction of this system is connected with cardiovascular and renal diseases. Regulation of RAAS is under the control of multiple intracellular mechanisms. Cyclic nucleotides and phosphodiesterases are the major regulators of this system since they control expression and activity of renin and aldosterone. In this review, we summarize known mechanisms by which cyclic nucleotides and phosphodiesterases regulate renin gene expression, secretion of renin granules from juxtaglomerular cells and aldosterone production from zona glomerulosa cells of adrenal gland. We also discuss several open questions which deserve future attention.

Sildenafil Citrate Downregulates PDE5A mRNA Expression in Women with Recurrent Pregnancy Loss without Altering Angiogenic Factors-A Preliminary Study

In our previous study, we showed that sildenafil citrate (SC), a selective PDE5A blocker, modulated NK cell activity in patients with recurrent pregnancy loss, which correlated with positive pregnancy outcomes. It was found that NK cells had a pivotal role in decidualization, angiogenesis, spiral artery remodeling, and the regulation of trophoblast invasion. Thus, in the current study, we determined the effects of SC on angiogenic factor expression and production, as well as idNK cell activity in the presence of nitric synthase blocker L-NMMA. Methods: NK cells (CD56⁺) were isolated from the peripheral blood of 15 patients and 15 fertile women on MACS columns and cultured in transformation media containing IL-15, TGF-β, and AZA—a methylation agent—for 7 days in hypoxia (94% N₂, 1% O₂, 5% CO₂). Cultures were set up in four variants: (1) with SC, (2) without SC, (3) with NO, a synthase blocker, and (4) with SC and NO synthase blocker. NK cell activity was determined after 7 days of culturing as CD107a expression after an additional 4h of stimulation with K562 erythroleukemia cells. The expression of the PDE5A, VEGF-A, PIGF, IL-8, and RENBP genes was determined with quantitative real-time PCR (qRT-PCR) using TaqMan probes and ELISA was used to measure the concentrations of VEGF-A, PLGF, IL-8, Ang-I, Ang-II, IFN–γ proteins in culture supernatants after SC supplementation. Results: SC downregulated PDE5A expression and had no effect on other studied angiogenic factors. VEGF-A expression was increased in RPL patients compared with fertile women. Similarly, VEGF production was enhanced in RPL patients’ supernatants and SC increased the concentration of PIGF in culture supernatants. SC did not affect the expression or concentration of other studied factors, nor idNK cell activity, regardless of NO synthase blockade.

Erectile Dysfunction after Kidney Transplantation

Patients with kidney transplantation often have a worse quality of life than the general population. One of the reasons for this, in male patients, is the high prevalence of erectile dysfunction. This is mainly due to the presence of comorbidities, surgery for kidney transplantation, adverse drug effects, psychological changes related to chronic disease, as well as hyperprolactinemia and hypogonadism. Whenever these endocrine dysfunctions occur after kidney transplantation, they must be corrected with appropriate treatment, i.e., testosterone replacement therapy. Administration of the phosphodiesterase-5 inhibitor (PDE5i) sildenafil at the recommended posology does not significantly alter the pharmacokinetics of the calcineurin inhibitors cyclosporin A or tacrolimus and does not impair kidney allograft function. Tacrolimus increases the peak concentration and prolongs the half-life of PDE5i in kidney transplant patients and, therefore, daily administration cannot be recommended due to the significant drop in blood pressure. Intracavernous injection or topical application of alprostadil can be a second-line option for the treatment of erectile dysfunction after kidney transplantation, which does not alter cyclosporine concentrations and does not deteriorate kidney function. Finally, penile prostheses can be successfully implanted following pelvic organ transplantation after eliminating the risk of infection associated with surgery.

Phosphodiesterase-5 gene (PDE5A) polymorphisms are associated with progression of childhood IgA nephropathy

The phosphodiesterase-5 (PDE-5) gene is highly specific to cyclic GMP (cGMP) and several experimental studies have shown that the nitric oxide/cGMP pathway plays an important role in the pathogenesis of glomerulonephritis, including IgA nephropathy (IgAN). The present study was conducted to investigate the association among 16 single nucleotide polymorphisms (SNPs) of PDE5A and childhood IgAN. The genotyping data from 160 patients with childhood IgAN and 454 controls showed a significant difference in rs13124532 (codominant, P = 0.005; dominant, P = 0.005). Furthermore, patient subgroup analysis revealed an association between the development of proteinuria (>4 and <or=4 mg/m(2)/h) and rs13124532 (codominant, P = 0.008; dominant, P = 0.011), and between the nephrotic range proteinuria (> 40 mg/m(2)/h) and rs11734241 (dominant, P = 0.035), rs12510138 (dominant, P = 0.028), rs13134665 (dominant, P = 0.025), rs3822192 (dominant, P = 0.027), rs10013305 (dominant, P = 0.020), rs1480940 (dominant, P = 0.020), rs1480936 (dominant, P = 0.019), rs11947234 (dominant, P = 0.019), and rs2127823 (dominant, P = 0.026). The pathological findings showed that rs13124532 had an association with podocyte foot process effacement (codominant, P = 0.035; dominant, P = 0.044) and with pathological progression (codominant, P = 0.046). Our results suggest that PDE5A is associated with increased disease susceptibility, pathological progression, and development of proteinuria in childhood IgAN.

Systemic and metabolic effects of PDE5-inhibitor drugs

Phosphodiesterase type-5 inhibitor (PDE5-i) drugs were first marketed in 1998 (sildenafil) for 'ondemand' treatment of male erectile dysfunction (ED) of any origin. They selectively inhibit intrapenile PDE5 isoenzyme which in turn increases intracellular cyclic guanosine monophosphate levels, thus resulting in prolonged relaxation of cavernosum smooth muscle cells and facilitating the erectile process. Since 2003, two new molecules (tadalafil and vardenafil) have been introduced, resulting in greater interest in these compounds and leading patients to ask for more prescriptions from their doctors. The vast use of PDE5-i in diabetic and cardiovascular ED patients led researchers to investigate their possible extra sexual effects. Several studies investigating their effects on endothelium, coronary and pulmonary circulation, inferior oesophageal sphincter and kidney functions have appeared and, finally, sildenafil was approved for the treatment of pulmonary arterial hypertension. Recent animal studies highlighted a possible interaction between chronic PDE5 inhibition and glucose homeostasis which occurs through a marked improvement of high fat diet induced insulin resistance. If this data is extended to humans, a new scenario will be opened for the chronic use of PDE5-i for sexual rehabilitation along with cardiovascular and metabolic benefits.

Influence of a single dose of 20 mg tadalafil, a phosphodiesterase 5 inhibitor, on ambulatory blood pressure in subjects with hypertension

AIMS

To test the non-inferiority of a single dose of tadalafil 20 mg compared with placebo with respect to 26-h mean ambulatory systolic and diastolic blood pressure in treated and untreated hypertensive subjects.

METHODS

A multicentre, randomized, double-blind, placebo-controlled crossover study in 114 subjects with hypertension (36 subjects on no therapy with daytime mean ambulatory blood pressure >/= 140/85 mmHg; 38 subjects on two to four classes of antihypertensive agents with daytime mean ambulatory blood pressure >/=140/85 mmHg and 40 subjects on two to four classes of antihypertensive agents with ambulatory blood pressure < 140/85 mmHg).

RESULTS

Overall tadalafil reduced mean ambulatory blood pressure monitor systolic and diastolic blood pressure by 4.8 mmHg [95% confidence interval (Cl) 3.7, 5.9; P < 0.01] and 2.9 mmHg (95% CI 1.9, 3.6; P < 0.01), respectively, compared with placebo. In hypertensive subjects with uncontrolled blood pressure on two to four classes of antihypertensive agents (n = 36) tadalafil reduced mean ABPM systolic and diastolic blood pressure by 7.5 mmHg (95% CI 5.4, 9.6; P < 0.01) and 4.3 mmHg (95% CI 6.1, 8.9; P < 0.01) compared with placebo.

CONCLUSIONS

In patients with uncontrolled hypertension on multiple agents the addition of tadalafil 20 mg lowered mean 26-h blood pressure.

Differential effects of the phosphodiesterase type 5 inhibitors sildenafil, vardenafil, and tadalafil in rat aorta

Presumably, the vasorelaxant properties of phosphodiesterase type 5 (PDE5) inhibitors are similar in isolated blood vessels. We aimed to explore the mechanisms underlying the vasorelaxation induced by the selective PDE5 inhibitors sildenafil, vardenafil, and tadalafil in the rat aorta. Aortic rings were mounted in 5-ml organ baths, and concentration-response curves for PDE5 inhibitors (0.0001-10 microM) were constructed in phenylephrine (PE)-precontracted endothelium-intact and -denuded rings. Cyclic nucleotides were measured using enzyme immunoassay kits. Sildenafil, vardenafil, and tadalafil concentration dependently relaxed aortic rings and increased cGMP, but not cAMP, concentrations. Endothelium denudation caused marked rightward shifts in the curves to sildenafil (45-fold), tadalafil (21-fold), and vardenafil (251-fold). Maximal responses to sildenafil and tadalafil were substantially reduced (38 +/- 1% and 53 +/- 2%, respectively), whereas that evoked by vardenafil was not affected. Likewise, inhibition of NO synthase (N(omega)-nitro-L-arginine methyl ester, 100 microM), guanylyl cyclase (1H-[1,2,4]oxadiazolo [4,3,-a]quinoxalin-1-one, 10 microM), or scavenging of NO ([carboxy-PTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), 100 microM]) caused similar attenuation of the vasorelaxations evoked by PDE5 inhibitors. Sildenafil, tadalafil, and vardenafil significantly potentiated relaxations mediated by glyceryl trinitrate (0.0001-3 microM; 8-13-fold) and atrial natriuretic peptide (0.1-100 nM; 2-3-fold). Contractions evoked by CaCl(2) (0.01-5 mM) in PE-treated rings were significantly reduced (26 +/- 4%) by vardenafil, but not sildenafil or tadalafil, whereas phorbol 12,13-dibutyrate-induced contractions were not affected. Ouabain, cyclopiazonic acid, and calyculin A failed to affect vasorelaxations induced by the PDE5 inhibitors. These results suggest that vardenafil, but not sildenafil or tadalafil, affects Ca(2+) handling in the rat aorta in addition to increasing cGMP levels through inhibition of PDE5 to cause relaxation.

Inhibition of cGMP-specific phosphodiesterase type 5 reduces sodium excretion and arterial blood pressure in patients with NaCl retention and ascites

In the present study, we tested the hypothesis that inhibition of renal phosphodiesterase type 5 (PDE5) in patients with liver cirrhosis and ascites increases sodium excretion. The effect of sildenafil citrate was studied in a randomized double-blind. placebo-controlled crossover study. Diuretics were withdrawn, and a fixed sodium diet (100 mmol/day) was given to the patients for 5 days before both study days. After a 60-min basal period, eight patients received either oral sildenafil (50 mg) or placebo. Glomerular filtration rate (GFR) and renal blood flow (RBF) were determined by 99mTc-diethylenetriamine-pentaacetate and (131)I-hippuran clearances. In human nephrectomy specimens, PDE5 mRNA was expressed at similar levels in the cortex (n = 6) and inner medulla (n = 4). Histochemical staining showed PDE5 immunoreactivity in collecting ducts and vascular smooth muscle. At baseline, cirrhotic patients exhibited elevated plasma concentrations of ANP, renin, ANG II, and aldosterone that did not differ on the 2 study days. Basal sodium excretion was similar at the 2 study days (median 17 and 18 mmol, respectively), and patients were in positive sodium balance. Sildenafil increased heart rate, plasma renin activity, plasma ANG II, and aldosterone concentrations significantly after 60 min. Plasma cGMP concentration was increased after 120 and 180 min, and urinary sodium excretion and mean arterial blood pressure were decreased significantly at 120 and 180 min. Plasma ANP concentration, GFR, and RBF did not change after sildenafil. In patients with ascites and cirrhosis, inhibition of PDE5 did not promote natriuresis but led to increased plasma levels of the renin-angiotensin-aldosterone system.

Hemodynamic effects of phosphodiesterase 5 and angiotensin-converting enzyme inhibition alone or in combination in conscious SHR

The regional hemodynamic responses to continuous 4-day infusion of UK-357,903 [1-ethyl-4-{3-[3-ethyl-6,7-dihydro-7-oxo-2-(2-pyridylmethyl)-2H-pyrazolo[4,3-d]pyrimidin-5-yl]-2-(2-methoxyethoxy)-5-pyridylsulphonyl}piperazine] (266 microg kg(-1) h(-1)) alone and in combination with a low dose of enalapril (10 microg kg(-1) h(-1)) were measured in conscious spontaneously hypertensive rats to test the hypothesis that the renin-angiotensin system may influence the cardiovascular consequences of inhibition of phosphodiesterase 5 (PDE5) by UK-357,903 or vice versa. UK-357,903 alone caused a fall in mean blood pressure (-12.1 mm Hg) associated with vasodilatation in the mesenteric and hindquarters vascular beds. The only way in which the effects of enalapril given alone differed significantly from those of the vehicle was in causing mesenteric vasodilatation, which developed over the 4 days of infusion. UK-357,903 given in combination with enalapril caused hypotension (-17.8 mm Hg) and vasodilatation in the renal, mesenteric, and hindquarter vascular beds. There was evidence of a significant interaction between the effects of the two compounds on renal Doppler shift and vascular conductance with the combined action of the two compounds being greater than the sum of their individual effects. However, although there was a trend for the combination to have greater effects than either of the individual agents on blood pressure and mesenteric vascular conductance, there was no statistical evidence of an interaction. The results indicate that inhibition of the renin-angiotensin system uncovers additional renal vasodilator effects of UK-357,903, and/or inhibition of PDE5 enhances the renal vasodilator effects of angiotensin-converting enzyme inhibition.

Haemodynamic effects of the selective phosphodiesterase 5 inhibitor, UK-357,903, in conscious SHR

1. Regional haemodynamic responses to a continuous, 4-day infusion of the selective phosphodiesterase type 5 inhibitor, UK-357,903 (0.133 or 1.33 mg x kg(-1) h(-1)) were measured in conscious spontaneously hypertensive rats, and compared with those of enalapril (1 mg x kg(-1) h(-1)). 2. Both doses of UK-357,903 caused modest reductions in mean blood pressure that were not dose-dependent and only significantly different from the vehicle effects on Day 1 of the study (mean -11.8 and -15.3 mmHg for low and high doses, respectively). UK-357,903 had mesenteric and hindquarters vasodilator effects, which were, again, similar for both dose levels and only significantly different from vehicle on Day 1. Neither dose of UK-357,903 affected renal vascular conductance or heart rate. 3. Although the haemodynamic effects of UK-357,903 were not clearly dose-related and some appeared to wane with time, geometric mean plasma levels of UK-357,903 increased in proportion to dose, and were sustained throughout the infusion period. Furthermore, plasma cyclic guanosine monophosphate, a biomarker of phosphodiesterase 5 inhibition, was persistently elevated, and increased with increasing dose. 4. Enalapril caused a fall in mean blood pressure on day 1 (-14.1 mmHg) that was associated with dilatation in renal, mesenteric and hindquarters vascular beds. The haemodynamic effects of enalapril were sustained or increased over the 4-day infusion, although plasma free drug levels were stable. 5. In conclusion, we have shown regional and temporal changes in the haemodynamic effects of UK-357,903, which may be due to activation of compensatory mechanisms, but there were no signs of functional compensation to the cardiovascular effects of enalapril.