REGULATION IN THE CENTRAL NOREPINEPHRINE NEUROTRANSMISSION INDUCED IN VIVO BY ALPHA ADRENOCEPTOR ACTIVE DRUGS’

BRIiSTRUP, Cus AND MOGENS NIELSEN: Regulation in the central nonepinephnine neurotransmission induced in vivo by alpha adrenoceptor active drugs. J. Pharmacol. Exp. Then. 198: 596-608, 1976. The level of the two major norepinephnine metabolites, 3-methoxy-4-hydnoxyphenyl-glycol (MOPEG) and 3,4-dihydroxyphenylglycol (DOPEG), was estimated in the central nervous system of rats to study receptor-mediated regulation of release in vivo as reflected in biochemical changes. The norepinephnine receptor stimulating drug clonidine (0.02-0.5 mg/kg) decreased the level of endogenous total MOPEG. The accumulation of 3H-MOPEG and 3H-DOPEG was decreased by clonidine (0.5 mg/kg) regardless of whether 3H-tyrosine or 3H-dopamine was used as precursor of 3H-norepinephnine. In contrast to clonidine, the two alpha adrenocepton blocking drugs, phenoxybenzamine (20 mg/kg) and aceperone (20 mg/kg), induced an increase in endogenous total MOPEG and also an increase in 3H-MOPEG and 3H-DOPEG regardless of the precursor used. These results indicate that clonidine decreases th