Erectile response to topical, intraurethral and intracorporal pharmacotherapy in a rat model of spinal cord injury.

Abstract

In order to compare the erectile response to topical, intraurethral and intracorporal administration of vasoactive substances in neurologically intact and spinal cord injured (SCI) rats, a standard rat model of SCI using impact trauma at the level of T10 was employed, comparing the tumescence of 24 SCI and 25 control rats. Four weeks after SCI, the effect of vasoactive substances on erectile function was evaluated. Under ketamine anesthesia, the penis was exposed and intracorporal pressure (ICP) was monitored using saline infusion cavernosometry through a 24-gauge catheter inserted into one corpus cavernosum. Changes in ICP were recorded in response to the topical and intraurethral (IU) application of minoxidil (0.1 ml, 2% solution) and 2% nitroglycerin (NTG) ointment (0.1 gm), as well as the intracorporal (IC) administration of papaverine (0.0001-0.10 mg/kg). Results indicated that the mean baseline ICP was 8 +/- 5 mmHg for SCI and 9 +/- 4 mmHg for control rats. No response to topical therapy onto the undegloved penis was noted in either SCI or control rats. IU application of minoxidil to the degloved phallus developed ICP greater than that achieved with topical minoxidil; the topical application of NTG was less effective. In SCI rats, IC papaverine injection achieved an ICP of 56.9 +/- 24.3 mmHg, whereas papaverine in control rats generated an ICP of 43.5 +/- 38.8 mmHg. A greater increase in ICP at lower doses of each agent occurred in SCI than in control rats. We conclude that only the degloved phallus responded to topical vasoactive pharmacotherapy. Although both topical and IU applications of NTG and minoxidil increase ICP, tumescence was significantly less than that achieved with IC injection of papaverine. The IU application of minoxidil demonstrated significantly greater activity than other topical therapies. SCI rats displayed a supersensitive response to all modes of pharmacologic erectile therapy.