Central and peripheral prazosin binding: an in vitro autoradiographic study in the rat

Using an in vitro autoradiographic technique the binding of [3H]prazosin to brain, spinal cord, heart and vascular tissue was studied. Histologically prepared tissue sections were incubated in 5 nM [3H]prazosin or 5 nM [3H]prazosin in the presence of 100 microM unlabelled prazosin base in order to establish sites exhibiting specific prazosin binding. Dense prazosin binding sites were found in all arterial tissue examined except mesenteric artery. Dense prazosin binding was also found in cardiac tissue. Prazosin binding to veins was present sometimes but often absent. Prazosin does not readily pass the blood brain barrier and in this in vitro study the only area, within the central nervous system, showing specific prazosin binding sites was the olfactory bulb. The selective binding of prazosin, an alpha 1-adrenoceptor antagonist, to arterial and cardiac tissue would suggest that the antihypertension induced by prazosin is mediated by a peripheral action.