An Inhibitor of Cerebral Uptake of Noradrenaline in Jaundiced Blood Plasma

Abstract

Summary: The permeability of the blood-brain barrier to noradrenaline was estimated in rats with bile duct li gation by intracarotid injection of [14Cl-L-noradrenaline, 3H20, and [ll3mInjethylene diamine tetraacetate (EDTA) under pentobarbitone anaesthesia, Brain uptake of [14Clnoradrenaline was expressed as a percentage of that of 3H20 (brain uptake index, B UI) and corrected for the "blood background" by the 113mIn. The BUI of noradren aline (1.20 ± 0.19) was not increased in jaundice (0.78 ± 0.18). The capacity of oxygenated homogenates of rat Cerebral blood flow is not normally very sensitive to intravascular noradrenaline (Olesen, 1972). This is considered to be due to the inaccessibility of the arteriolar smooth muscle rather than to a lack of receptors, since cerebral vasoconstriction can be induced by microinjection of noradrenaline into the perivascular space of pial arteries (Wahl et aI., 1972) or into the interstitial fluid of the hypothalamus (Cranston and Rosendorff, 1971). On the other hand, intravascular administration, when the cere bral endothelium has been opened by osmotic shock, has caused an increase in cerebral blood flow, probably secondary to an increase in cerebral metabolic rate (Mackenzie et aI., 1976).A moderate reduction in cerebral blood flow was found with intracarotid infusion of noradrenaline (8 or 16 j.Lg min -1 ) in baboons with bile duct ligation (Bloom et aI., 1975). It was suggested that this hy persensitivity to noradrenaline might be due to an