“2 The conformationally restricted enkephalin analogues [2‐D‐penicillamine, 5‐L‐cysteine ] enkephalin (DPLCE), [ 2‐D‐penicillamine , 5‐L‐penicillamine] enkephalin (DPLPE) and [2‐D‐penicillamine, 5‐D‐penicillamine] enkephalin (DPDPE) produced dose‐related inhibition of reflex bladder contractions when administered by the i.c.v.”