Effect of Ionizing Radiation on the Pyridine Nucleotides of Thymocytes

Abstract

The pyridine nucleotides of thymocytes have been examined following irradiation of the cells in vivo or in vitro. NAD was found to constitute about 95% of the total oxidized pyridine nucleotides in thymocytes while the level of NADH2 was found to be very low. There is a rapid loss of NAD from thymocytes following irradiation in vitro or in vivo which is evident with as little as 25 rads. There is no concomitant rise in the NADH2 levels following irradiation. The loss of NAD occurs principally from the nucleus of the cell and is characterized by an intracellular release of NADase from the mitochondria and nucleus into the cytoplasm. Following irradiation there is a reduced capacity for thymocytes to synthesize NAD from 7-C14-nicotinamide either in vitro or in vivo. The administration or presence of nicotinamide produces an unphysiological increase in the level of NAD in whole thymus or thymocytes in suspension. The level of NAD in treated cells is higher than in untreated controls following irradiation. This effect is not produced by nicotinic acid, cysteamine, L-cysteine, or promethazine. The administration of nicotinamide does not prevent the development of pyknotic degeneration in irradiated thymocytes. There is no change in the RNA content of the thymus under the conditions which reduce the NAD content.

The Use of Chromium-51 as a Sensitive Quantitative Criterion of Early Radiation Damage to Rat Thymocytes

“…'The mechanis~n that is affected in the intact cell by iriadiation which reduces the uptake of Cr51 is not a t present known. Con~parable sensitivities have been reported for the loss of NAII and damage to the electron transport chain in thymocl-tes (14,15). R a t red cells and mouse ascites cells which exhibit no obvious d a~n a g e following doses of the irlagnitude used in this work during the ti111es studied also show no changes i11 their uptake of Cr51.…”

“…Several early sensitive biochemical changes have been reported in thymocytes following irradiation (13)(14)(15)(16). Vittorio et al (17, 1 8 ) have dernoilstrated that the uptake of Cr51 by tissues is an excellent indication of radiation dainage and tissue repair and also serves as an index of the efficacy of protective coinpounds.…”

“…described (13). Unless otherwise stated thymocytes were prepared and incubated in a modified Tyrode's medium (14) but with a glucose concentration of 0.0053 Jf. Cell concentrations were of the order of lo8 cells per ml and were counted on a Coulter counter.…”

“…Mitochondria were prepared in physiological potassium chloride and nuclei in 0.25 ,If sucrose -0.003 M calcium chloride as previously described (14). Protein and nucleic acids were separated from the washed, sedimented cells by the method of Tyner et al (20).…”

The Nature of the Radiation-Induced Lesion of the Electron Transport Chain of Thymus Mitochondria

“…Such release of proteins following irradiation has been reported previously (9-1 1) as well as has the release of various enzymes (12)(13)(14). Whether this protein corresponds with any of the proteins reported (15, 16) to be structural or functional components of the E T C in mitochondria from other tissues remains to be determined.…”