The effect of sildenafil on apomorphine-evoked increases in intracavernous pressure in the awake rat

J Urol. 1999 May;161(5):1707-12.


Purpose: The aim of this study was to develop a quantitative, awake animal model to investigate the effect of sildenafil on centrally-evoked erectile activity.

Methods: Intracavernous pressures were recorded in awake, male Sprague Dawley rats after administration of apomorphine (100 or 250 microg./kg. subcutaneously). Sildenafil (100 microg./kg. intravenously) was then given 10 min. after a second dose of apomorphine. The time to first response, duration of response, and peak intracavernous pressure and area under the response, were measured before and after sildenafil.

Results: Apomorphine produced rhythmic increases in intracavernous pressure. The pressure increase consisted of two components. The amplitude of the first, tonic response was 58 +/- 3 mm. Hg, and a superimposed, burst-like increase in pressure elevated this further to 81 +/- 6 mm. Hg. Bilateral transection of the pudendal nerves abolished the burstlike pressure changes; bilateral transection of the cavernous nerves prevented both responses. The duration of the apomorphine-induced increase in intracavernous pressure was significantly (p = 0.003) prolonged by sildenafil (100 microg./kg.) from 37 +/- 4 to 62 +/- 11 s (n = 6). The overall intracavernous pressure response to apomorphine (100 microg./kg.), measured as the area under the curve, was significantly (p = 0.003) increased by sildenafil (100 microg./kg.) from 67 +/- 8 to 142 +/- 31 units (n = 6). N-nitro-L-arginine methyl ester (40 mg./kg. intravenously) prevented the apomorphine-induced responses.

Conclusions: Monitoring intracavernous pressures in the awake rat represents a simple model to evaluate the effect of drugs on erectile function. Using this model we have shown that apomorphine elicits a rise in intracavernous pressure that can be prolonged by sildenafil. These results suggest that there may be a role for the combination of apomorphine and sildenafil in the management of erectile dysfunction.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Apomorphine / pharmacology*
  • Dopamine Agonists / pharmacology*
  • Male
  • Penile Erection / drug effects*
  • Phosphodiesterase Inhibitors / pharmacology*
  • Piperazines / pharmacology*
  • Pressure
  • Purines
  • Rats
  • Rats, Sprague-Dawley
  • Sildenafil Citrate
  • Sulfones


  • Dopamine Agonists
  • Phosphodiesterase Inhibitors
  • Piperazines
  • Purines
  • Sulfones
  • Sildenafil Citrate
  • Apomorphine