Validation of a triiodothyronine (T3) ELISA for mouse fecal samples.

Acquiring sufficient blood for hormone analysis in mice can be a limiting step. Hormone analysis techniques using non-invasive sample collection have been vigorously developed for endangered species, from whom blood sampling is prohibited, or from species that are otherwise difficult to handle in a laboratory setting. Because there are interactions between glucocorticoids and thyroid hormones (T3 and T4), reducing the animal's "distress" during sample collection is imperative. Measurement of fecal T3 provides less sensitive, baseline information regarding thyroid function while permitting a non-invasive technique for more frequent sampling. We demonstrated that using a methanol extraction protocol produced the most reliable fecal T3 measurement in an enzyme-linked immunosorbent assay (ELISA). We found that during a thyroid hormone-treated state, fecal and plasma T3 measurements from mice are directly related, while during a methimazole-treated state, fecal and plasma T3 measurements from mice are inversely related. Fecal samples are a useful way to monitor thyroid hormone function in laboratory mice.