determined after drugs were added to the bath in 10 to 50 u03bcl amounts and washed out with two 10 ml portions of buffer after noting their maximum effects this assay was performed according to the description by g henderson et al brit j pharmacol 46 764 1972 both vasa deferentia were dissected out of mice and mounted singly through two platinum ring electrodes in a 10 ml organ bath the bath contained krebs bicarbonate solution that was continuously bubbled with 95 o 2 and 5 co 2 the organ bath was maintained at 37 u00b0 c the tissue was attached to an isometric transducer and stimulated transmurally with rectangular pulses 0 1 mz 1 ms duration supramaximal voltage drugs were added cumulatively to the bath in 10 to 50 u03bcl amounts and washed out after noting their maximum effect the antagonist potency of the compound of example i bntx was compared to the activity of nti and naltrexone in vitro on the mouse vas deferens mvd and guinea pig ileum gpi preparations each compound 100 nm was incubated for 15 min with the tissue prior to adding graded doses of a standard agonist for determination of an ic 50 value the standard agonists employed were d ala 2 d leu 5 enkephalin dadle morphine m and ethylketazocine ek these are selective for delta.