The effects of the 2-amino-tetrahydronaphthalene derivative M7, a selective alpha 2-adrenoceptor agonist in vitro.

M7 was originally reported to be a selective presynaptic alpha 2-adrenoceptor agonist in the pithed rat preparation. Subsequent work showed that M7 also stimulated postsynaptic alpha 2-adrenoceptors in this preparation, producing a pressor response. We have now investigated the selectivity of M7 for alpha 1-and alpha 2-adrenoceptors in vitro. Our results demonstrate that M7 is very potent stimulating presynaptic alpha 2-adrenoceptors in the rat vas deferens and postsynaptic alpha 2-adrenoceptors in the dog saphenous vein. However, at higher doses M7 is also an alpha 1-adrenoceptor agonist, its ED50 at alpha 1-adrenoceptors being approximately 60 fold greater than that at postsynaptic alpha 2-adrenoceptors. It is clear that the postsynaptic effects of M7 will depend upon the relative proportions of alpha 1-and alpha 2-adrenoceptors contained in the tissue under study.