The effect of beta-blockade therapy on serum thyroxine binding globulin (TBG) concentration

Non-specific beta-blockade with either propranolol or nadolol was shown not to reduce serum TBG concentration in 20 untreated thyrotoxic patients, but to cause significant reductions in the same subjects once they were rendered euthyroid. Similar reductions were also seen in a group of 10 clinically and biochemically euthyroid subjects, who were under investigation for anxiety or mild angina. Since nadolol does not possess the membrane stabilising properties of propranolol, nor is it metabolized like propranolol, the effect on TBG concentration would appear to be due to beta-blockade.