Evaluation of adrenal function in mice by measurement of urinary excretion of free corticoids

Methods for the determination of urinary total free corticoids and urinary free corticosterone in small laboratory rodents are described. Total free eorticoids and free corticosterone were determined in samples of 50–200 μl urine by a competitive protein binding method using human plasma transcortin as the source of binding protein. For both methods employed the reliability criteria were satisfactory. The validity of both methods was tested by measuring both total free corticoids and free corticosterone in urine samples of mice with the obese-hyperglycemic syndrome (gene symbol C57BL/6J-ob/ob) and their lean controls (gene symbol C57B1/6J). Measurements were taken from urine samples under basal conditions and after adrenal stimulation or suppression. Urinary corticoid levels were significantly different between the two mouse lines, 15 ng/day for the lean and 75 ng/day for the obese mice, reflecting plasma corticosterone levels. After stimulation by ACTH urinary corticoids rose 3–5-fold whereas suppression by dexamethasone was followed by a decrease to very low levels. The contribution of corticosterone to total corticoids averaged 50% in lean and 30% in obese mice. It is concluded that urinary total excretion of free corticoids as well as urinary excretion of free corticosterone offer a valuable parameter of adrenal function in mice. Furthermore, when small laboratory rodents are used, under many circumstances measurements in urine are more advantageous than measurements in plasma.