Intracerebroventricular morphine produces diuresis 24 h after previous dynorphin/morphine treatment

The effect of dynorphin A-(1-13) on morphine-induced urine output was studied in the rat. The previous simultaneous intracerebroventricular (i.c.v.) injection of dynorphin (20 micrograms/rat) and morphine (20 micrograms/rat) altered the response of rat given morphine (20 micrograms/rat) 24 h later, producing a 3-fold increase in urine output. In contrast, previous injection of dynorphin or morphine alone had no effect.