[Stereoselectively different cardiovascular effects of the enantiomers of 2 N-methylated barbiturates in the rat].

The (-)-enantiomers of 1-methyl-5-phenyl-5-propyl barbituric acid (MPPB) and 1-methyl-5-phenyl-5-butyl barbituric acid (MPBB) injected i.v. depress blood pressure and heart rate of rats to a fourfold higher degree than the (+)-enantiomers. These stereoselectively different actions on blood pressure and heart rate are abolished after pretreatment with reserpine. Stereoselective differences are not existent with regard of the negative inotropic action (isolated left atrium and papillary muscle), the negative chronotropic action (isolated right atrium) and the blockade of tension development induced by noradrenaline at the isolated ductus deferens. The enantiomers of MPPB and MPBB exhibit stereoselectively different influence on the sympathetic outflow of intact rats during barbiturate-induced hypotension and bradycardia: 1 min after injection the efferent activity of neck sympathetic nerve is increased only if the (+)-enantiomers are given (twofold of the control). 5 min after application only in the presence of the (-)-enantiomers a slight increase of the efferent activity is observed.