Centrally induced reduction in sympathetic tone — A postsynaptic α-adrenoceptor-stimulating action of imidazolines

摘要: Naphazoline or oxymetazoline (both 30 μg/kg) were injected into the cisterna magna of anaesthetized cats and reduced blood pressure, heart rate electrical discharge small fibre bundles preganglionic sympathetic splanchnic nerve. Cats depleted endogenous noradrenaline by pretreatment with reserpine (5 mg/kg, 18 h) α-methyl-p-tyrosine) twice 300 2 h). In these animals, intracisternal injection μg/kg exerted a decrease discharges similar to that described for non-pretreated animals. noradrenaline-depleted 1 clonidine also decreased discharges. It is concluded imidazolines exert their sympathoinhibitory cardiovascular effects stimulation postsynaptic α-adrenoceptors in CNS. In isolated rat vas deferens, was much weaker agonist (intrinsic activity (i.a.) < 0.1) than naphazoline (i.a. 0.6 0.8 respectively). All three considerable competitive antagonism against noradrenaline, being most potent antagonist (pA2: 6.0; 5.0; 5.5). The order agonistic activities on deferens different from other peripheral adrenergic systems indicates α-adrenoceptors. possibility receptor differences CNS discussed.