[Dioxin-l] phytoestrogen feeds confounds low-dose ED effects?

[Tony Tweedale]

[bcc's to various ED researchers].  sorry if you're already aware of this.
--

A team from AstraZeneca Central Tox Lab, responding by correspondence to a
discussion of the confounding role of phytoestrogens or other natural ED
compounds in lab animal feeds (Thigpen et al. _EHP_:107:182-3 ('99)), warn:

"..The most subtle estrogenic efects yet reported for synthetic estrogens,
the incr. in male mouse prostate weight reported by vom Saal and his
colleagues (6-9) were observed in animals fed Purina chow 5001, a diet
identified by Thigpen (1) as being richer in phyoestrogens...]"
	-John Ashby et al "Uterotrophic Activity of a "Phytoeestrogen-Free"
Rat Diet' _Env Health Persp's_ 108:1:A12-13 ('00)

The 4 vom Saal, Nagel & Welshons studies cited include estrogenic effect
tests of bis-PhenolA, octylphenol, DES, estrogens and methoxychlor, inter
alia.  They include the notable finding (supported by a known mechanism,
that hormone receptors can be shut-off by too many hrmone molecules) that
lower doses cause more potent effect than higher doses -- findings that I
have frequently cited in making arguments on various listservs.

The Zeneca team report their new studies on the ED (uterine growth) effects
of feeds, which show (confirmed once) that AIN-76A feed is apparantly the
only feed causing uterine growth.  Apparantly negative for uterine growth
is the Purina chow 5001 reported to be "rich[] in phyoestrogens" that Dr's.
vom Saal et al. used according to Ashby et al. here.

All-in-al,l reason to be cautious in using these very low dose/powerful ED
effect studies.  No doubt studies will be published rpplicating, or not,
these vom Saal et al.  reports by repeating them w/ different feeds, free
of ED componds.