Effect of neonatal allylestrenol treatment and adult benzpyrene treatment on rat thymus glucocorticoid receptors.

1. Neonatal treatment with allylestrenol caused an increase in the number of glucocorticoid receptors in the thymus in the adult. 2. Benzpyrene treatment of adult animals persistently reduced the glucocorticoid receptor number in rats that were not submitted to neonatal treatment. This effect was not observed in adult animals following neonatal treatment with allylestrenol. 3. The experiment calls attention to the permanent effect of steroid imprinting and to the developmental stage dependence of the direction of imprinting. 4. The effect of neonatal steroid treatment on a later steroid influence is also demonstrated.