Effect of apomorphine on intracavernous pressure and blood pressure in conscious, spinalized rats

Apomorphine, given subcutaneously (s.c.), induces erection and bladder overactivity in rats through stimulation of dopamine (D1- and D2-like) receptors in the central nervous system. In paraplegic patients, apomorphine was reported to cause bladder overactivity. This suggests that apomorphine may have a spinal site of action also for stimulation of erection. The present study was initiated to evaluate the effect of apomorphine on erectile function in spinalized rats. Apomorphine (100 μg/kg, s.c.) was given to awake, unrestrained male Sprague-Dawley rats (300 g) with or without spinal cord injury, made at the Th 8 level 2 weeks before the experiment. Intracavernous pressure changes from baseline were evaluated as time to first response to apomorphine (TFR; sec), number of phasic pressure changes in the first 30 min (PP30), duration (D; sec) of the phasic pressure changes, the amount of increase in tonic peak pressure (TPP; cmH2O), and burst peak pressure (BPP; cmH2O). Blood pressure (cmH2O) was recorded via an intra-arterial catheter. Apomorphine, 100 μg/kg, caused no significant differences in TFR (217.8 vs 271.2), PP30 (6.4 vs 6.5), D (38.9 vs 37.6.), TPP (51.0 vs 54.0) and BPP (128.9 vs 160.4) between normal (n=8) and spinalized rats (n=6). However, blood pressure decreased significantly more in spinalized than in normal animals (17.7 vs 43.3; P<0.05). The results suggest that both in normal rats, and in rats with spinal cord injury, apomorphine given s.c., can produce erection. This finding supports the use of apomorphine for treatment of erectile dysfunction in paraplegia patients. However, due consideration should be given to possible decreases in blood pressure.