Comparative evaluation of lisuride and terguride, ergot alkaloid derivatives, on the field-stimulated vas deferens of mouse.

The ergot alkaloid derivatives, lisuride (LIS) and terguride (TDHL), known to interact with central dopamine receptors as agonist and partial agonist, respectively, were studied on the field-stimulated mouse vas deferens, where recently the existence of presynaptic dopamine receptors has been evidenced. LIS was a competitive antagonist at prejunctional alpha 2 and DA1 receptors situated on the sympathetic nerve terminals of the mouse, with a pA2 value of 9.2 and 9.1, respectively. LIS was also able to antagonize the effects of LY 171555, selective DA2 agonist, but the type of interaction cannot be conceptualized in terms of competitive antagonism. Likewise, the type of interaction of TDHL with dopaminergic and adrenergic agonist-activated sites is not suggestive of a competitive antagonism. Based on these results, it seems that central and peripheral pharmacologic profiles of LIS and TDHL cannot be overlapped, LIS being a potent DA1- and alpha 2-antagonist with a high degree of specifity for these receptors.