I just found a site that states that the Syntocinon nasal spray is used in labour (for the same reason as the injection) with humans. They don't mention dogs though. Here is the link:
Syntocinon® - Oxytocin | Buy Syntocinon Nasal Spray
This site explains why oxytocin is used and when, but they also make the point that the nasal spray shouldn't be used for this purpose:
Oxytocin and Dogs - Chinaroad Lowchens of Australia
There is also some interesting uses of oxytocin (also known as the love hormone) to help animals overcome shyness, to aid in social development of autistic people and to make men more sensitive!
