Impaired Cavernous Reinnervation after Penile Nerve Injury in Rats with Features of the Metabolic Syndrome

Authors

  • Matthew R. Nangle BSc, PhD,

    Corresponding author
    1. Pain Management Research Institute and Kolling Institute of Medical Research, University of Sydney at Royal North Shore Hospital, St. Leonards, New South Wales, Australia;
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  • Joseph Proietto MBBS, PhD,

    1. Department of Medicine (Austin Health & Northern Health), Heidelberg Repatriation Hospital, University of Melbourne, Heidelberg Heights, Victoria, Australia
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  • Janet R. Keast BSc, PhD

    1. Pain Management Research Institute and Kolling Institute of Medical Research, University of Sydney at Royal North Shore Hospital, St. Leonards, New South Wales, Australia;
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Matthew Nangle, BSc, PhD, Pain Management Research Institute, University of Sydney, Level 13, Kolling Building, Royal North Shore Hospital, St Leonards, Sydney, NSW 2065, Australia. Tel: (61) 2-9926-4967; Fax: (61) 2-9926-7105; E-mail: stish@med.usyd.edu.au

ABSTRACT

Introduction.  The metabolic syndrome is a cluster of cardiovascular risk factors that predispose toward the development of diseases such as diabetes. Erectile dysfunction (ED) is common in men with metabolic syndrome, but its etiology is poorly understood. Pro-erectile nitrergic nerves innervating penile erectile tissue are also susceptible to mechanical injury during pelvic surgical procedures, which can lead to sexual dysfunction.

Aims.  The aims of this article are: (i) to examine erectile function in an experimental model of metabolic syndrome, the phosphoenolpyruvate carboxykinase (PEPCK)-overexpressing rat; and (ii) to study function and cavernous reinnervation after penile nerve crush injury, which permits regeneration, in transgenic rats.

Methods.  We analyzed the density of noradrenergic and nitrergic nerves and performed organ bath pharmacology to assess neurogenic activity.

Main Outcome Measures.  By analyzing changes in neural structure, function, and pharmacologic responses of cavernous tissue after nerve crush injury, we were able to reveal neurologic deficits in rats with metabolic syndrome.

Results.  Animals with features of metabolic syndrome did not develop notable changes in cavernous autonomic nerve density or nerve-evoked smooth muscle activity. However, regeneration of nitrergic nerves after crush injury in transgenic rats was impaired compared with injured controls. This was manifested as a deficit in axon regrowth and responses to axon activation. However, unlike injured controls, injured PEPCK-overexpressing rats did not develop a reduced maximal response to the nitric oxide (NO) donor, sodium nitroprusside. This suggests preserved NO responsiveness in tissues from rats with metabolic syndrome, despite impaired regeneration and return of function.

Conclusions.  This study revealed that rats with features of metabolic syndrome display impaired cavernous nerve regeneration after penile nerve injury, but the degree of functional impairment may be attenuated due to reduced plasticity of NO signaling. This reinnervation deficit may be of clinical relevance for understanding why ED persists in some (particularly aged) men after pelvic surgery. Nangle MR, Proietto J, and Keast JR. Impaired cavernous reinnervation after penile nerve injury in rats with features of the metabolic syndrome. J Sex Med 2009;6:3032–3044.

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