Effects of Corticosterone, cAMP, cGMP, Ca2+, and Protein Kinase C on Apoptosis of Mouse Thymocytes Induced by X-ray Irradiation1.

Objective To observe the effects of signal factors of corticosterone (CS), cAMP, cGMP, Ca²⁺ and protein kinase C (PKC) on lymphocyte apoptosis in mouse thymus induced by X-rays of 4 Gy in vitro. Methods The DNA lytic rate for thymocytes was measured by fluorospectrophotometry. Results The DNA lytic rate for thymocytes 4-8 hours after irradiation with 2-8 Gy was significantly higher than that in the control (P<0.01). As compared with the control, the DNA lytic rate for thymocytes treated with 0.01 µmol/L CS (P<0.01), 50 ng/mL cAMP (P<0.01), 0.05-0.4 µg/mL ionomycin (lono, P<0.05 or P<0.01) or 0.05-0.4 ng/mL phorbol myristate acetate (PMA, P<0.05 or P<0.01), respectively, was significantly increased, while the rate for thymocytes treated with 50 ng/mL cGMP was not significantly increased. The DNA lytic rate for thymocytes treated with 0.01 µmol/L CS (P<0.01), 50 ng/mL cAMP (P<0.01), 0.2 and 0.4 µg/mL lono (P<0.05), and 0.2 and 0.4 ng/mL PMA (P<0.05) plus 4-Gy irradiation, respectively, was significantly higher than that treated with single 4-Gy irradiation, while the rate for thymocytes treated with 50 ng/mL cGMP plus 4-Gy irradiation was not increased. When both 0.4 µg/mL lono and 0.4 ng/mL PMA acted on the thymocytes, the DNA lytic rate for thymocytes was significantly higher than that in the control (P<0.01), the DNA lytic rate for thymocytes treated with both 0.4 µg/mL lono and 0.4 ng/mL PMA plus 4-Gy irradiation was significantly higher than that treated with single 4-Gy irradiation (P<0.05), but was not significantly higher than that treated with 0.4 µg/mL lono plus 4-Gy irradiation or 0.4 ng/mL PMA plus 4-Gy irradiation. Conclusion CS, cAMP, Ca²⁺, and PKC signal factors can promote thymocyte apoptosis induced by larger dose X-rays. [ABSTRACT FROM AUTHOR]