The effect of prazosin of pre- and post-synaptic alpha-receptors in the pithed rat.

1. Prazosin had a marked inhibitory effect on post-synaptic alpha-receptors in the pithed rat, as measured by the blood pressure response to the cumulative administration of clonidine. 2. Prazosin had no inhibitory effect, however, on the pre-synaptic alpha-receptor, as measured by the clonidine-induced reduction in the tachycardia produced by stimulation of the cardiac nerves. 3. These results suggest that prazosin has a selective antagonistic affinity for post-synaptic alpha-receptors.