Metrics for Evaluation of Age-Related Changes in Erectile Capacity in a Rodent Model


George Christ, PhD, Wake Forest Institute for Regenerative Medicine, Wake Forest University Health Sciences, Medical Center Blvd, Winston-Salem, NC 27157, USA. Tel: 336-713-7296; Fax: 336-713-7290; E-mail:


Introduction.  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).

Aim.  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.

Main Outcome Measures.  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 (r2 = 0.886) and old (r2 = 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 ≥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 cmH2O and 0.6 ± 0.02, respectively) than young (106 ± 3 cmH2O and 0.75 ± 0.02, respectively) rats (P < 0.0001).

Conclusion.  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. Zhao W, Sato Y, Melman A, Andersson K-E, and Christ G. Metrics for evaluation of age-related changes in erectile capacity in a rodent model. J Sex Med 2009;6:1885–1892.