Plasma corticosterone during postnatal ontogenesis in rats: comparison of protein-binding and fluorometric method.

Competitive protein-binding method was used for determination of plasma corticosterone levels in rat during postnatal ontogenesis until 600 days of age. The level of corticosterone was high after birth, decreased until 5th day of life and then again increased at the end of the second week. During adolescence, when the sexual differentiation begins the levels of plasma corticosterone in females become permanently higher than those of males. Moreover, the comparison of plasma corticosterone level as measured with the aid of competitive protein-binding method and fluorometric method was described in hypophysectomised, stressed and normal male rats. The correlation between both methods was satisfactory, but the results obtained with a competitive protein-binding method were, on an average, by 35% lower. The specificity, precision and recovery of competitive protein-binding assay were found to be satisfactory. This method was found to be of advantage for a determination of plasma corticosterone level in small laboratory animals because of a small volume of plasma necessary.