Good morning. We look forward to your questions and comments.

I have a follow up to the comment by Kevin Osteen on reproductive cycles. Most female vertebrates, including women, have some sort of cycle such as menstrual (primates) or estrous (rodents) cycles. Thus, our bodies/brains are subjected to continual fluctuations in hormones. This is normal. When we are exposed to exogenous environmental chemicals this type of exposure can be acute or continuous, but is almost never cyclic. This may be another mechanism for "unexplained" actions of exogenous chemicals.

Andrea -- I agree with what you are saying, but I have thought about the pattern of delivery of chemicals like perchlorate that have a short half-life. In this case, at least in animal models in which the chemical is dissolved in the drinking water, the daily pattern of drinking will dictate the cyclic pattern of exposure (and perhaps disruption). Since about 80% of water is consumed in the first few hours after lights off, this could be an important pattern (that may or may not be "natural")
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