The Effect of X Irradiation on Cardiac β-Adrenergic Receptors in the Rabbit

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Abstract
Cardiac .beta. receptors in rabbits were studied at different times following lethal (5 Gy [gray]) or supralethal (10 Gy) whole-body X irradiation. Using the radioctive ligand [125I]iodocyanopindolol, it was found that the maximal binding capacity, as determined from the Scatchard plot, decreased from 298.2 .+-. 13.2 fmole/mg protein in controls to 142.4 .+-. 5.5 fmole/mg 3 days after 10 Gy whole-body X irradiation, whereas the dissociation constant was only slightly affected. Three days after an exposure to 5 Gy, maximal binding capacity was reduced slightly and tended toward control values at day 7. Local irradiation of the cardiac region with 10 Gy reduced cardiac .beta. receptors to 218 .+-. 7 fmol/mg (73% of control) after 3 days. About half the effect of radiation on cardiac .beta. receptors originates from a direct action of radiation on the heart tissue, the rest being due to abscopal systemic reactions.