Age-related changes in adrenocorticoid and opioid receptor capacity of thymus-derived lymphocytes in rats

The experiments were performed in 4-day, 4-week, and 4-month old rats. The total binding capacity of high affinity receptors for 3H-naloxone and 3H-corticosterone in thymus-derived lymphocytes was measured in vitro. There was no change in the affinity constant of the receptors for the ligands during the life-time mentioned before. The maximal binding capacity for 3H-corticosterone in thymus-derived lymphocytes showed a marked increase in 1-month and 4-month old ages as compared to the values obtained by the end of the first postnatal week. In contrast, the maximal binding capacity of lymphocytes for 3H-naloxone showed a significant decline with age. Changes in the binding capacity for the two ligands refer to changes in composition of of cells within the thymus and to alterations in cell system in sensitivity to either corticosteroids or opioids.