Effects of noradrenaline on cytosolic concentrations of Ca(2+) in cultured corpus cavernosum smooth muscle cells of the rabbit

Erectile Dysfunction in Men on the Rise: Is There a Link with Endocrine Disrupting Chemicals?

Erectile dysfunction (ED) is one of the most prevalent chronic conditions affecting men. ED can arise from disruptions during development, affecting the patterning of erectile tissues in the penis and/or disruptions in adulthood that impact sexual stimuli, neural pathways, molecular changes, and endocrine signalling that are required to drive erection. Sexual stimulation activates the parasympathetic system which causes nerve terminals in the penis to release nitric oxide (NO). As a result, the penile blood vessels dilate, allowing the penis to engorge with blood. This expansion subsequently compresses the veins surrounding the erectile tissue, restricting venous outflow. As a result, the blood pressure localised in the penis increases dramatically to produce a rigid erection, a process known as tumescence. The sympathetic pathway releases noradrenaline (NA) which causes detumescence: the reversion of the penis to the flaccid state. Androgen signalling is critical for erectile function through its role in penis development and in regulating the physiological processes driving erection in the adult. Interestingly, estrogen signalling is also implicated in penis development and potentially in processes which regulate erectile function during adulthood. Given that endocrine signalling has a prominent role in erectile function, it is likely that exposure to endocrine disrupting chemicals (EDCs) is a risk factor for ED, although this is an under-researched field. Thus, our review provides a detailed description of the underlying biology of erectile function with a focus on the role of endocrine signalling, exploring the potential link between EDCs and ED based on animal and human studies.

The promise of inhibition of smooth muscle tone as a treatment for erectile dysfunction: where are we now?

Ten years ago, the inhibition of Rho kinase by intracavernosal injection of Y-27632 was found to induce an erectile response. This effect did not require activation of nitric oxide-mediated signaling, introducing a novel target pathway for the treatment of erectile dysfunction (ED), with potential added benefit in cases where nitric oxide bioavailability is attenuated (and thus phosphodiesterase type 5 (PDE5) inhibitors are less efficacious). Rho-kinase antagonists are currently being developed and tested for a wide range of potential uses. The inhibition of this calcium-sensitizing pathway results in blood vessel relaxation. It is also possible that blockade of additional smooth muscle contractile signaling mechanisms may have the same effect. In this review, we conducted an extensive search of pertinent literature using PUBMED. We have outlined the various pathways involved in the maintenance of penile smooth muscle tone and discussed the current potential benefit for the pharmacological inhibition of these targets for the treatment of ED.

Chronic ethanol consumption induces cavernosal smooth muscle dysfunction in rats

OBJECTIVES

To investigate the effects of chronic ethanol consumption on nitric oxide (NO)-mediated relaxation in rat cavernosal smooth muscle (CSM).

METHODS

Male wistar rats were divided into 2 groups: control and ethanol. CSM obtained from both groups were mounted in organ chambers for measurement of isometric tension. Contraction of the strips was induced by electrical field stimulation (EFS, 1-32 Hertz) and phenylephrine. We also evaluated the effect of ethanol consumption on the relaxation induced by acetylcholine (0.01-1000 micromol L(-1)), sodium nitroprusside (SNP, 0.01-1000 micromol L(-1)), or EFS (1-32 Hz) in strips precontracted with phenylephrine (10 micromol L(-1)). Blood ethanol, serum testosterone levels, and basal nitrate generation were determined. Immunoexpression of endothelial NO synthase (eNOS) and inducible NO synthase (iNOS) was also accessed.

RESULTS

Ethanol intake for 4 weeks significantly increased noradrenergic nerve-mediated contractions of CSM in response to EFS. The endothelium-dependent relaxation induced by acetylcholine decreased after the ethanol treatment. Ethanol consumption decreased serum testosterone levels but did not affect the nitrate levels on rat CSM. The mRNA and protein levels for eNOS and iNOS receptors were increased in CSM from ethanol-treated rats.

CONCLUSIONS

Ethanol consumption reduces endothelium-dependent relaxation induced by acetylcholine, but does not affect SNP or EFS-induced relaxation, suggesting that ethanol disrupts the endothelial function. Despite the overexpression of eNOS and iNOS in ethanol-treated rats, the impaired relaxation induced by acetylcholine may suggest that chronic ethanol consumption induces endothelial dysfunction.

Alpha(1A)-adrenoceptors mediate contractions to phenylephrine in rabbit penile arteries

BACKGROUND AND PURPOSE

Maintained penile erection depends on the absence of alpha-adrenoceptor (alpha-AR) activation and so can be facilitated by alpha-blockers. This study seeks the alpha(1)-AR subtypes involved in order to inform the pro-erectile consequences of subtype selective blockade.

EXPERIMENTAL APPROACH

Wire myography was used with dorsal (nutritional supply) and cavernous (erectile inflow) penile arteries; standard alpha-AR-selective agonists and antagonists were employed to classify responses.

KEY RESULTS

In both penile arteries noradrenaline (NA) and phenylephrine (PE, alpha(1)-AR agonist) caused concentration-dependent contractions. Sensitivity to NA was increased by NA uptake blockers, cocaine (3 microM) and corticosterone (30 microM). PE responses were antagonised by phentolamine (non-selective alpha-AR: dorsal pK(B) 8.00, cavernous 8.33), prazosin (non-subtype-selective alpha(1)-AR: dorsal 8.60, cavernous 8.41) and RS100329 (alpha(1A)-AR selective: dorsal 9.03, cavernous 8.80) but not by BMY7378 (alpha(1D)-AR selective: no effect at 1-100 nM) or Rec15/2615 (alpha(1B)-AR selective: no effect at 1-100 nM). Schild analysis was straightforward in cavernous artery, indicating that PE activates only alpha(1A)-AR. In dorsal artery Schild slopes were low, though alpha(1A)-AR was still indicated. Analysis using UK 14,304 and rauwolscine indicated an alpha(2)-AR component in dorsal artery that may account for low slopes to alpha(1)-AR antagonists.

CONCLUSIONS AND IMPLICATIONS

Penile arteries have a predominant, functional alpha(1A)-AR population with little evidence of other alpha(1)-AR subtypes. Dorsal arteries (nutritional supply) also have alpha(2)-ARs. Thus, alpha-AR blockers with affinity for alpha(1A)-AR or alpha(2)-AR would potentially have pro-erectile properties; the combination of these perhaps being most effective. This should inform the design of drugs to assist/avoid penile erection.

APOE4 protects the cognitive development in children with heavy diarrhea burdens in Northeast Brazil

Polymorphisms in the apolipoprotein E (APOE) have constituted the major rationale to identify potential risk groups for developing late-onset Alzheimer's disease and help to predict recovery of cognitive function after brain injury. However, the APOE impact on cognitive development in children living in poor areas of the developing world, where we have discovered profound significant associations of early childhood diarrhea (at 0-2 y) with lasting impairments of growth, cognition, and school performance, is not known. Therefore, we conducted APOE genotyping in 72 Brazilian shantytown children under active surveillance since birth, using purified DNA extracted from buccal cell samples. We found a high frequency of APOE4 alleles (18% versus 9-11% expected) in children with lower diarrhea burdens. When we examined the children who experienced the heavier diarrhea burdens (greater than or equal to the median of seven illnesses in the first 2 y of life), those with APOE4 did significantly better in the coding subtest (p=0.01) when compared with APOE4-negative children with similar diarrhea burdens. Positive correlations between the APOE4 occurrence and coding scores remained, even after adjusting for family income, maternal education, and breast-feeding. Moreover, the APOE4-positive group, under heavy burdens of diarrhea, had preserved semantic fluency and the mean difference in fluency scores, p=0.025, a standardized coefficient for disproportional verbal fluency impairment. Our findings show that APOE4 is relatively common in favela children and suggest a protective role of the APOE4 allele in children with a history of heavy burdens of diarrhea in their first 2 y of life.

Inhibition of the tonic contraction in the treatment of erectile dysfunction

Erectile dysfunction (ED) reduces the quality of life. It is estimated that 52% of men have some degree of ED, which is associated with ageing. While it is clear that there are a variety of current treatment options for ED, each of these has drawbacks and contraindications. A better understanding of the physiological mechanisms involved in penile erection will provide new ways to treat ED. This review not only focuses on the vasoconstrictors and vasodilators that control the state of contraction and relaxation of the corpora cavernosa smooth muscle, but also presents a novel Ca(2+)-sensitising pathway that contributes to maintaining the penis in the non-erect state. Studies have shown that inhibition of the RhoA/Rho-kinase signalling pathway induces penile erection. Further understanding of this RhoA/Rho-kinase pathway may provide a novel alternative treatment for ED.

Ca2+-activated Cl- channels in corpus cavernosum smooth muscle: a novel mechanism for control of penile erection

Little is known of the excitatory mechanisms that contribute to the tonic contraction of the corpus cavernosum smooth muscle in the flaccid state. We used patch-clamp electrophysiology to investigate a previously unidentified inward current in freshly isolated rat and human corporal myocytes. Phenylephrine (PE) contracted cells and activated whole cell currents. Outward current was identified as large-conductance Ca(2+)-activated K(+) current. The inward current elicited by PE was dependent on the Cl(-) gradient and was inhibited by niflumic acid, indicative of a Ca(2+)-activated Cl(-) (Cl(Ca)) current. Furthermore, spontaneous transient outward and inward currents (STOCs and STICs, respectively) were identified in both rat and human corporal myocytes and derived from large-conductance Ca(2+)-activated K(+) and Cl(Ca) channel activity. STICs and STOCs were inhibited by PE and A-23187, and combined 8-bromoadenosine cAMP and 8-bromoadenosine cGMP decreased their frequency. When studied in vivo, chloride channel blockers transiently increased intracavernosal pressure and prolonged nerve-evoked erections. This report reveals for the first time Cl(Ca) current in rat and human corpus cavernosum smooth muscle cells and demonstrates its key functional role in the regulation of penile erection.