Variations in phytoestrogen content between different mill dates of the same diet produces significant differences in the time of vaginal opening in CD-1 mice and F344 rats but not in CD Sprague-Dawley rats.
BACKGROUND
The optimum test diet and rodent species/strain for evaluating endocrine-disrupting compounds (EDCs) are critical.


OBJECTIVE
We conducted studies to evaluate rodent species sensitivity and the effects of diets varying in phytoestrogen content on the time of vaginal opening (VO) in CD-1 mice, Fischer 344 (F344) rats, and CD Sprague-Dawley (S-D) rats.


METHODS
Mice were weaned on postnatal day (PND) 15 and rats on PND19 and randomly assigned to control or test diets. Body weights, food consumption, and time of VO were recorded.


RESULTS
The time of VO was significantly advanced in F344 rats fed diets containing daidzein and genistein, whereas these same diets did not advance VO in S-D rats. When animals were fed the AIN-76A diet spiked with genistein, time of VO was significantly advanced at all doses in CD-1 mice, at the two highest doses in F344 rats, and at the highest dose in S-D rats. The time of VO in F344 rats was more highly correlated with the phytoestrogen content than with the total metabolizable energy (ME) of 12 diets.


CONCLUSIONS
The S-D rat is less sensitive to dietary phytoestrogens compared with the F344 rat or the CD-1 mouse, suggesting that the S-D rat is not the ideal model for evaluating estrogenic activity of EDCs. The profound effects of dietary phytoestrogens on the time of VO, an estrogen-sensitive marker, indicate that a standardized open-formula phytoestrogen-free diet containing a low ME level should be used to optimize the sensitivity of estrogenic bioassays.
Thigpen
Julius E
JE
Comparative Medicine Branch, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, NC 27709, USA. thigpen@niehs.nih.gov
Setchell
Kenneth D R
KD
Padilla-Banks
Elizabeth
E
Haseman
Joseph K
JK
Saunders
Hannah E
HE
Caviness
Gordon F
GF
Kissling
Grace E
GE
Grant
Mary G
MG
Forsythe
Diane B
DB
D000818:Animals; D001835:Body Weight / Q000187:drug effects; D004032:Diet; D004734:Energy Metabolism / Q000187:drug effects; D005247:Feeding Behavior / Q000187:drug effects; D005260:Female; D019833:Genistein / Q000032:analysis / Q000494:pharmacology; D007529:Isoflavones / Q000032:analysis / Q000494:pharmacology; D051379:Mice; D048789:Phytoestrogens / Q000032:analysis* / Q000494:pharmacology*; D051381:Rats; D011916:Rats, Inbred F344; D017207:Rats, Sprague-Dawley; D014621:Vagina / Q000187:drug effects*
D007529:Isoflavones; D048789:Phytoestrogens; C004742:daidzein; D019833:Genistein