alpha 2-Adrenergic agonist and antagonist activity of the respective (-)-and (+)-enantiomers of 6-ethyl-9-oxaergoline (EOE).

The (-)-enantiomer of 6-ethyl-9-oxaergoline (EOE) inhibited contractions of the field-stimulated rat vas deferens in vitro, and produced mydriasis in anesthetized rats with an order of potency 1/2 and 1/5 that of clonidine, respectively. In contrast (+)-EOE competitively antagonized these responses to both (-)-EOE and clonidine with an order of potency 1/5 that of yohimbine. The data indicate that (-)- and (+)-EOE represent an unique example of enantiomers having opposing pharmacological activities upon alpha 2-adrenoceptors.