in the present study , therefore , the rank order of the potency of three endogenous opioid peptides , [ met5 ] -enkephalin , [ leu5 ] -enkephalin , and beta-endorphin , in three isolated preparations , guinea-pig ileum , mouse vas deferens , and rat vas deferens , was estimated in the presence of the mixture of three peptidase inhibitors , amastatin , captopril , and phosphoramidon .
C0205753
endogenous opioid peptides
C0014298
enkephalin