Why Oliguria occurs because of saline or dextrose?

hi,
i have a question that i have to answer to my prof. She asked me that "Why Oliguria occurs when saline or 5% dextrose is given to patient?"
i researched but i couldn't find proper answer. It seems these things are expected to increase urine not decrease.

I am sorry if i created thread at wrong place. And sorry for grammar or type mistakes. English isn't mother language of me.

Thanks for any help
Greetings from Turkey.