[Activity of cAMP System in Sheep Lymphocytes and Platelets Exposed to External γ-Radiation in vivo]

The activity of the cyclic adenosine-3,5-monophosphate (cAMP) in lymphocytes and platelets of sheep has been studied for 15 days after animal exposure to total external γ-radiation at a dose of 4 Gy (LD50/30). The basal and E1 stimulated activity of adenylate cyclase and phosphodiesterase activity were determined by the thinlayer chromatography technique, and the cAMP content was determined using RIA-kits with 125J. Modification was revealed in the cAMP system functioning in the cell populations studied from the first day following radiation exposure. In particular, the basal adenylate cyclase activity in lymphocytes increased 1.7-4.3 times at all study dates, and stimulated enzyme activity increased on days 1-7, 21-8.8-fold compared to the initial data. Platelets showed increase in the basal adenylate cyclase activity on days I and 7, 2.7 and 35 times, and stimulated activity at the same times--9 and 5.7 times, respectively. The adenylate cyclase stimulation coefficient in lymphocytes raised 1.8 and 2.3 times on days 1 and 5, respectively, on day 7 it corresponded to the initial data and on days 10-15 it dropped below the control. However in platelets, this parameter did not have significant differences from the initial data. The phosphodiesterase activity in lymphocytes increased 3-fold on day 3, 2.4-fold on day 7, and in platelets it practically remained at the control level. The cAMP content in lymphocytes dropped within the first 12 hours and on day 3, 2.71 and 2.38 times, respectively, whereas in platelets it decreased 3.08 times within 12 hours and increased 1.91 times on day.3. At other times the cAMP content in lymphocytes and platelets did not differ from the initial data. The results suggest that the identified modification of cAMP system activity in lymphocytes and platelets in various periods after exposure of animals is based on different mechanisms. In the early period, alteration in the enzyme activity of cAMP system and cAMP content is caused by radiation effects on cytoplasmic membrane of cells circulating in the peripheral blood of animals. In the later periods, the recorded variations in the cAMP system activity are defined by the prevalence in the blood of more resistant to radiation damage cell subpopulation with an enhanced activity of cAMP enzymes and cAMP concentration corresponding to unexposed animals.