Dopamine receptor profile of co-dergocrine (Hydergine) and its components

Co-dergocrine (Hydergine), an ergot preparation composed of four dihydrogenated peptide ergot alkaloids (dihydroergocornine, dihydroergocristine, dihydro-alpha-ergokryptine, dihydro-beta-ergokryptine, 3:3:2:1), has been reported to exert in vivo effects suggesting an interaction with dopaminergic systems. The present investigation provides evidence that, in the striatum of the rat, co-dergocrine and its components interact directly with D1- and D2-subtypes of dopamine receptors. In homogenates of rat striatum, co-dergocrine and three of its components (dihydroergocornine, dihydro-alpha-ergokryptine, dihydro-beta-ergokryptine) stimulate cyclic AMP formation (D1-receptor response) having similar EC50 values but different efficacies. The same compounds inhibit electrically evoked tritium overflow from rat striatal slices preincubated with [3H]choline (D2-receptor response) at about 50 times lower concentrations. Here again the compounds exhibit differential maximal effects. One component, dihydroergocristine, antagonises both receptor types. The effect of co-dergocrine in functional responses mediated by both D1- and D2-receptors seems to reflect the summation of the contribution of its components.