Effect of growth hormone on surface charge and electrophoretic mobility of thymocytes from young and aged rats

The electrophoretic mobility and surface charge of thymocytes was reduced on incubation of the cells with growth hormone in vitro. All cells in thymus were not found to be sensitive to the hormone. The proportion of cells whose surface charge was altered by the hormone was 65% in the thymocytes from 5-week-old rats. The subpopulation of hormone-sensitive cells was reduced to 19% of the total teased-out thymocytes in 1-year-old rats and was below the level of detection in thymocytes derived from 11/2-year-old rats. Analytical studies showed that the alteration in the surface charge of the hormone-sensitive subpopulation was nearly of the same order in thymocytes derived from 5-week and 1-year-old rats, suggesting that the binding capacity of the cells for the hormone was presumably similar at the two ages. On the other hand the quantitative preponderance of the subpopulation of cells sensitive to growth hormone diminishes with age, reaching insignificant levels at 11/2 years.