The effect of X irradiation on cardiac β-adrenergic receptors in the rabbit

Cardiac β receptors in rabbits were studied at different times following lethal (5 Gy) or supralethal (10 Gy) whole-body X irradiation. Using the radioactive 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 little 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 β receptors to 218 ± 7 fmole/mg (73% of control) after 3 days. The latter observation suggests that about half the effect of radiation on cardiac β receptors originates from a direct action of radiation on the heart tissue, the rest being due to abscopal systemic reactions.