Differential effects of chronic propranolol treatment on the phenotypic profile of thymocytes from immature and adult rats

To elucidate a putative role of beta-adrenoceptors in the modulation of int rathymic T-cell maturation, the expression of major differentiational antig ene (CD4/CD8 and TCR alpha beta) on the thymocytes from both immature (aged 21 day at the beginning of the treatment) and adult (a,oed 75 days at the beginning of treatment) male rats subjected to a 15-day-long propranolol tr eatment (0.40 mg/100 g/day, s.c.) was analyzed by two- and one-color flow c ytometry, respectively. Rats of matched age injected with saline served as controls. The propranolol treatment in immature but not adult rats caused a significant reduction in both the relative thymus weight and total thymocy te yield. In addition, a significant increase in the percentage of CD4(+)8( +) double-positive cells, with a proportional decrease in the relative prop ortion of CD4(+)8(-) single positive cells, was found in immature rats. In contrast, a slight but significant decrease in the percentage of CD4(+)8(+) cells with a parallel increase in the relative proportion of CD4+8- cells was found in adult rats. In both groups of rats, the percentage of TCR alph a beta(total) thymocytes was increased: in immature rats this was due to an increase in the percentage of TCR alpha beta(low) thymocytes, while in the adult rats it reflected a rise in the relative proportion of TCR alpha bet a(high) cells. In conclusion, the study revealed that propranolol treatment in both immature and adult rats alters the relative proportion of CD4(+)8( +) and CD4(+)8(-) thymocytes, but in opposite fashion, and the data suggest that this treatment affects distinct fractions within the population of CD 4(+)8(+) thymocytes with respect to expression of TCR alpha beta. The resul ts also indicate that, regardless of rat sexual maturity, the development o f thymocytes towards CD4(-)8(+) T-cells is relatively insensitive to long-l asting P-adrenoceptor blockade. (C) 2000 Elsevier Science B.V. All rights r eserved.