Use of transgenic (knockout) mice reveals a site distinct from the alpha2A-adrenoceptors for agmatine in the vas deferens.

The inhibitory effect of agmatine on electrically induced contractions was studied in vas deferens of Adra 2a transgenic mice lacking alpha(2A)-adrenoceptors. Agmatine and clonidine caused a concentration-dependent inhibition of twitches. However, while agmatine showed a similar pIC(50) value in control and transgenic mice, the pIC(50) value for clonidine was about 30-fold lower in knockout mice. In both strains, yohimbine shifted the curve for clonidine, but not for agmatine, even when a 100-fold higher concentration of yohimbine was employed. Our results indicate that inhibition by agmatine in mouse vas deferens is not simply due to interactions with alpha(2)-adrenoceptors in our experimental conditions.