title: Metrics for evaluation of age-related changes in erectile capacity in a rodent model.
abstract: BACKGROUND
  Stimulation of the cavernous nerve elicits increases in intracavernosal pressure (ICP) and visible penile erection (VPE) in rats. The observed penile erection can be characterized by the change in ICP and the ratio of ICP over blood pressure (BP; systemic blood pressure).
  
  
  OBJECTIVE
  We evaluated correlations between ICP, BP, ICP/BP, and VPE, and the magnitude of the nerve stimulation required to elicit those responses in order to evaluate age-related changes in erectile function in a rodent model.
  
  
  METHODS
  Nine young (3 months) and 10 old (18 months) rats were used. Under anesthesia cavernous nerve stimulation was performed at stimulation strengths ranging from 0.1 to 10 mA.
  
  
  METHODS
  The ICP, BP, ICP/BP, and VPE responses to cavernous nerve stimulation were quantified and compared.
  
  
  RESULTS
  Significant correlations were observed between ICP and ICP/BP in both young (r(2) = 0.886) and old (r(2) = 0.962) rats. If the ratio ICP/BP was taken as a metric of VPE and non-erection, then the threshold value for observing a VPE in the majority of animals was > or =0.5 in both young and old rats. However, higher current stimulation was required in the old than in the young animals to achieve erections. Moreover, both the maximal ICP and ICP/BP ratios achieved during erection were also lower in the old (85 +/- 2 cmH(2)O and 0.6 +/- 0.02, respectively) than young (106 +/- 3 cmH(2)O and 0.75 +/- 0.02, respectively) rats (P < 0.0001).
  
  
  CONCLUSIONS
  Old rats without obvious comorbidities were capable of penile erections, but those erections were accompanied by reduced ICP responses to cavernous nerve stimulation, implying apparently reduced penile rigidity. Taken together our current observations indicate that ICP, ICP/BP, and VPE provide useful metrics/indices of erectile capacity/function, and, moreover, that improved understanding of the inter-relationships among these parameters provides a frame work for further exploration of the mechanistic basis for age-related erectile dysfunction.
authors.affiliation: Wake Forest Institute for Regenerative Medicine, Wake Forest University Health Sciences, Medical Center Blvd., Winston-Salem, NC 27157, USA.
authors.forename: Weixin
authors.initials: W
authors.lastname: Zhao
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Sato
authors.forename: Arnold
authors.initials: A
authors.lastname: Melman
authors.forename: Karl-Erik
authors.initials: KE
authors.lastname: Andersson
authors.forename: George
authors.initials: G
authors.lastname: Christ
mesh_terms: D000367:Age Factors; D000818:Animals; D018783:Impotence, Vasculogenic / Q000188:drug therapy*; D008297:Male; D023421:Models, Animal; D010410:Penile Erection / Q000187:drug effects*; D010413:Penis / Q000187:drug effects* / Q000294:innervation; D010726:Phosphodiesterase Inhibitors / Q000627:therapeutic use*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013223:Statistics as Topic; D014665:Vasodilator Agents / Q000627:therapeutic use*
chemical_list: D010726:Phosphodiesterase Inhibitors; D014665:Vasodilator Agents