There is a substantial body of indirect pharmacologic evidence which has been interpreted as indicating that presynaptic receptor-mediated modulation of noradrenergic vascular neurotransmission is altered in the mesenteric vasculature of SHR. Enhanced release of either total 3H or 3H-NE after prelabeling with 3H-NE has been demonstrated to occur from the mesenteric vasculature of SHR after administration of isoproterenol or angiotensin II. However, evidence has now been obtained in the mesenteric vasculature demonstrating that there are no differences in the release of endogenous NE from adult SHR preparations versus that from adult WKY preparations.