Okie doughkie, I have my medical biochem book here and it is pretty vague. It is a nonapeptide, withat disulfide bridge in it (thus the instability) The major function that implied in the text is that it is mainly resposible for lactation in pregnant women.

The whole thing about the acceleration of birth, welll, is because it is injected into uterine smooth muscle.

Oddly enough, this protein (or peptide if you are picky) is released in the body with a carrier protein. Vasopressin (or ADH (Not Alcohol De Hydrogenase)) follows the same route. One last thing to note is they have very short plasma half life (2-4 minutes)

Well that is the word from the biochem of humans book. Harpes is a good book for about $40 US, it has a crap load of answers.
Wally