Effect of caffeine on response of rabbit isolated corpus cavernosum to high K+ solution, noradrenaline and transmural electrical stimulation.

1. Caffeine has wide-ranging activities on smooth muscles, including contractile and relaxant effects. The aim of the present study was to examine the activity of caffeine on rabbit corpus cavernosum (RCC). 2. The effects of caffeine (0.5-4.0 mmol/L) on the response of RCC to high K+ solution, noradrenaline (NA) and transmural electrical stimulation (EFS) were studied in a tissue bath system. 3. Caffeine did not contract the RCC. However, 0.5-4.0 mmol/L caffeine caused concentration-dependent relaxation of tension development in high-K+ (120 mmol/L) solution in contrast with the solvent control. At 4.0 mmol/L caffeine, high-K+ solution-induced tone of the RCC was reduced by 73.4 +/- 7.3%. Caffeine (0.5-4.0 mmol/L) also concentration-dependently relaxed NA (12.5 micro mol/L)-induced tonic contraction of the RCC. At 4.0 mmol/L caffeine, NA-induced tone of the RCC was reduced by 41.1 +/- 7.0%. Incubation of RCC in 2.0 mmol/L caffeine for 30 min prior to EFS (1-40 Hz) caused a marked rightward shift in the frequency-response curve. 4. The results of the present study suggest that caffeine exhibits relaxant activity on rabbit cavernosal smooth muscle and the mechanism of this activity possibly involves inhibition of Ca2+ signalling.