Testicular lactate dehydrogenase and sorbitol dehydrogenase activity after intratesticular injection of dynorphin and morphine in male rats.

Testicular lactate dehydrogenase (LDH) and sorbitol dehydrogenase (SDH) activity were measured at 1 and 4 hr following intratesticular injection of morphine and dynorphin. Twenty five and 50 micrograms doses of morphine sulfate significantly reduced LDH activity at 1 hr after injection. Five and 25 micrograms doses of dynorphin reduced LDH activity both at 1 and 4 hr after treatment. Testicular SDH activity was increased by morphine at 1 hr followed by a decrease at 4 hr. Both doses of dynorphin significantly reduced SDH activity at 1 and 4 hr after treatment. These results indicate paracrine regulatory role for opioids in testicular metabolism.