Dear Cindy Engl:
I'm afraid that the relationship between breastfeeding, prolactin levels,
 and postpartum depression is indirect at best.  There have been three
studies that have looked at prolactin and ppd:  One found that HIGHER levels
were associated with ppd, one found that LOWER levels were associated with
ppd, and a third found NO ASSOCIATION.

The same type of mixed results have also been found for the other hormonals
and their metabolites.  What I have found is that breastfeeding and ppd
prevention both flourish in the same types of environments.  When mothers
have lots of emotional and practical support, when they are eating enough and
wisely (particularly complex carbs), when they are getting enough rest
(certainly related to support), and when they feel that someone gives a damn
about how they are doing, then they are much less likely to become depressed
and more likely to be able to breastfeed.

I have a couple of handouts I use for in-service training that would be
helpful.  Also, I would like to recommend my book "Postpartum depression: A
comprehensive approach for nurses"  It is available from Sage Publications
(805) 499-0721, and has the advantage of being both cheap and short (and of
course, a comprehensive review of the literature).

In the meantime, the other three references are:
George, AJ Copeland JRM & Wison KCM (1980). Serum prolactin and the
postpartum blues syndrome.  Brit j of Psychiatry, 70, 102-103.

Nott PN, Franklin M Armitage C & Gelder MG (1976) Hormonal changes in mood in
the puerperium. Brit J of Psychiatry, 128, 379-383

Vemer HM & Rolland R (1981). The dynamics of prolactin secretion dduring the
puerperium in women. Clinical Endocrinology, 15, 155-163.

Good luck with your work.

Kathy Kendall-Tackett