FIGURE 2.

Effect of stimulation of D₁ and D₂ dopamine receptors on proliferation of activated normal T cells and Jurkat cells by [³H]thymidine incorporation assay. Treated cells were cultured for 72 h, and radiolabeled thymidine was added 18 h before termination of experiments. Incorporated radioactivity was measured as representative of cellular proliferation. Intracellular cAMP concentration also was measured from these treatment groups. A, stimulation of D₁ dopamine receptors by its specific agonist (SKF, SKF 82526) in CD3/CD28-stimulated normal T cells showed significant dose-dependent inhibition of proliferation with maximum inhibition found at a 1 μm concentration. In contrast, no significant inhibition of proliferation was observed in CD3/CD28-stimulated Jurkat cells following D₁ agonist treatment. B, CD3/CD28-stimulated normal T cells showed significant dose-dependent inhibition of proliferation following stimulation of D₂ DA receptors by a specific D₂ agonist (Q, quinpirole hydrochloride), and maximum inhibition was found at 2 μm concentration, but no significant inhibition of proliferation was observed in Jurkat cells following D₂ DA receptor agonist treatment. Results are mean ± S.E. of six separate experiments (*, p < 0.05). C, intracellular cAMP measured at different time points after D₁ agonist stimulation (1 μm) showed a significantly elevated level in normal activated T cells where the peak was reached at 5 h and then declined. But similar treatment failed to elevate intracellular cAMP pool of Jurkat cells. D, stimulation of D₂ dopamine receptors could not inhibit the cAMP concentration in CD3/CD28-activated Jurkat cells. Results are mean ± S.E. of six separate experiments (*, p < 0.05). Culture and treatment protocols are as described under “Experimental Procedures.”