Nitric oxide-mediated erectile effects of galantide but not galanin in vivo

Galanin Administration Partially Restores Erectile Function After Cavernous Nerve Injury and Mediates Endogenous Nitrergic Nerve Outgrowth In Vitro

BACKGROUND

Previously, we found that the neuropeptide galanin was strongly upregulated soon after bilateral cavernous nerve injury (BCNI) and that galanin and its receptors were expressed in nitrergic erectile innervation. Galanin has been observed to exert neuroregenerative effects in dorsal root ganglion neurons, but evidence for these effects in the major pelvic ganglion (MPG) after BCNI is lacking.

AIM

To evaluate the neurotropic effects of galanin receptor agonists and antagonists in vitro in nitrergic neurons and MPG and in vivo in rats after BCNI.

METHODS

Male Sprague-Dawley rats underwent BCNI and sham surgery. Organ culture and single-cell neuron culture of the MPG were performed. Osmotic pump treatment with the galanin agonist in vivo and measurement of erectile response to electrostimulation after BCNI, immunohistochemical localization of galanin and receptors in the human neurovascular bundle, and myographic analysis of rat corpus cavernosum smooth muscle relaxation to galanin receptor agonists were investigated.

OUTCOMES

Neurite outgrowth in vitro and erectile response to electrostimulation after BCNI in vivo, immunohistochemical localization of galanin and receptors, and penile muscle relaxation in vitro.

RESULTS

Galanin showed neurotrophic action in vitro and inhibition of endogenous galanin significantly impaired neurite outgrowth in nitrergic but not in sympathetic MPG neurons. In vivo administration of a selective galanin receptor-2 agonist, M1145, resulted in partial recovery of erectile function (EF) after BCNI. Galanin did not act as a direct vasodilator on corpus cavernosum muscle strips.

CLINICAL TRANSLATION

Endogenous neurotrophins such as galanin could be used as a strategy to improve EF for patients after BCNI from radical prostatectomy.

STRENGTHS AND LIMITATIONS

We evaluated the effect of galanin on nerve regeneration and EF recovery in vivo and in vitro. Limitations include the lack of washout period for the in vivo experiment and absence of differences in the expression of neuronal markers between treatment groups.

CONCLUSIONS

We identified galanin as a potential endogenous mechanism for nerve regeneration after BCNI, which could play a physiologic role in EF recovery after radical prostatectomy. In vivo treatment with exogenous galanin was beneficial in enhancing EF recovery after BCNI, but further research is necessary to understand the underlying mechanisms. Weyne E, Hannan JL, Gevaert T, et al. Galanin Administration Partially Restores Erectile Function After Cavernous Nerve Injury and Mediates Endogenous Nitrergic Nerve Outgrowth In Vitro. J Sex Med 2018;15:480-491.

Increased expression of the neuroregenerative peptide galanin in the major pelvic ganglion following cavernous nerve injury

INTRODUCTION

Erectile dysfunction (ED) remains a frequent complication of radical prostatectomy due to injury to the cavernous nerves (CNs). A recent microarray showed the neuropeptide galanin to be one of the most strikingly upregulated genes in the rat major pelvic ganglion (MPG) after bilateral CN crush injury (BCNI).

AIM

The aim of this study is to evaluate the temporal regulation of galanin in the MPG after BCNI and its relationship to functional nerve regeneration.

METHODS

Changes in galanin, galanin receptor (galR), and c-JUN mRNA expression were assessed in Sprague-Dawley rats after sham operation (n = 10) and at 48 hours (n = 10), 7 (n = 10), 14 (n = 5), 21 (n = 5), 30 (n = 5), and 60 (n = 5) days after BCNI using quantitative PCR. Erectile function was assessed by measuring intracavernous pressure (ICP) divided by mean arterial pressure (MAP) during CN electrostimulation. Immunohistochemistry was performed on the MPG in sham-operated animals and 5 days after BCNI.

MAIN OUTCOME MEASURES

ICP/MAP upon CN stimulation; galanin, galR1, -2, -3, and c-JUN mRNA expression at various time points after BCNI; and nNOS, galanin, and galR distribution in the MPG of sham-operated rats and after BCNI.

RESULTS

After BCNI, ICP/MAP values quickly deteriorate, while after 60 days, spontaneous restoration of erectile responses to CN stimulation is observed, reflecting CN regeneration. Galanin mRNA in the MPG is up to 186-fold upregulated compared with sham-operated rats at 48 hours and 7 days after BCNI and gradually declines with increasing time from injury, whereas galanin receptor expressions decrease and c-JUN gradually increases. Galanin expression shows a strong inverse correlation with erectile responses to CN stimulation with time from injury. Injured MPGs show a colocalization between galanin- and nNOS-positive neuronal cell population in the MPG.

CONCLUSIONS

Galanin is upregulated in the MPG in the early phase after CN injury after which it gradually decreases and is present in nNOS-positive neurons of the ganglion. We hypothesize that galanin upregulation is an important factor in the endogenous neuroregenerative response to CN injury.

Analysis of erectile responses to BAY 41-8543 and muscarinic receptor stimulation in the rat

INTRODUCTION

Soluble guanylate cyclase (sGC) is the receptor for nitric oxide (NO) and in pathophysiologic conditions where NO formation or bioavailability is impaired, erectile dysfunction (ED) occurs.

AIM

The aim of this study was to investigate erectile responses to the sGC stimulator BAY 41-8543 in physiologic and pathophysiologic conditions.

METHODS

Increases in intracavernosal pressure (ICP) in response to intracavernosal (ic) injections of BAY 41-8543 were investigated in the anesthetized rat.

MAIN OUTCOME MEASURES

Increases in ICP/MAP in response to ic injections of BAY 41-8543 and the interaction of BAY 41-8543 with exogenous and endogenously released NO were investigated and the effect of the sGC stimulator on cavernosal nerve injury was assessed. The mechanism of the increase in ICP/MAP in response to ic injection of acetylcholine was investigated.

RESULTS

The ic injections of BAY 41-8543 increased ICP/MAP and the duration of the response. BAY 41-8543 was less potent than sodium nitroprusside (SNP) and ic injections of BAY 41-8543 and SNP produced a larger response than the algebraic sum of responses to either agent alone. Simultaneous ic injection of BAY 41-8543 and cavernosal nerve stimulation produced a greater response than either intervention alone. Atropine and cavernosal nerve crush injury decreased the response to nerve stimulation and ic injection of BAY 41-8543 restored the response.

CONCLUSION

These data show that BAY 41-8543 has significant erectile activity and can synergize with exogenous and endogenously released NO. This study shows that atropine and nerve crush attenuate the response to cavernosal nerve stimulation and that BAY 41-8543 can restore the response. The results with atropine, L-NAME and hexamethonium indicate that the response to ic injection of acetylcholine is mediated by muscarinic receptors and the release of NO with no significant role for nicotinic receptors. These results suggest that BAY 41-8543 would be useful in the treatment of ED.

AM, Casey DB, Dhaliwal JS, Murthy SN, Kadowitz PJ. Intracavernosal administration of sodium nitrite as an erectile pharmacotherapy

It has been reported that sodium nitrite (NaNO2) can act as a storage form of nitric oxide (NO) that can have beneficial pharmacologic actions. The present study was undertaken to investigate the effects of NaNO2 on erectile function in the rat. The intracavernosal (i.c.) injection of NaNO2 produced dose-related increases in i.c. pressure and decreases in systemic arterial pressure. NaNO2 was 1000-fold less potent than sodium nitroprusside in increasing i.c. pressure. Increases in i.c. pressure in response to NaNO2 were attenuated by the nitric oxide synthase (NOS) inhibitor N-nitro-l-arginine methyl ester (l-NAME). The increases in i.c. pressure in response to NaNO2 were not altered by the xanthine oxidoreductase inhibitor allopurinol. The decreases in systemic arterial pressure in response to i.c. injections of NaNO2 were attenuated by allopurinol and were either unchanged or increased by l-NAME. These data suggest that NaNO2 is converted to vasoactive NO in the corpora cavernosum and systemic vascular bed of the rat by different mechanisms. The present data suggest that the conversion of NaNO2 to vasoactive NO is mediated by NOS in the corpora cavernosum and by xanthine oxidoreductase in the systemic vascular bed of the rat. These data show NaNO2 can serve as a NO donor that increases erectile activity in the rat.