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The Extrathyroidal Effect of D,L-Propranolol on 3,3',5'-Triiodothyronine, 3',5'-Diiodothyronine, 3,3'-Diiodothyronine, and 3'-Monoiodothyronine Kinetics^*

Departments of Internal Medicine E and Clinical Chemistry, Frederiksberg Hospital DK-2000 Copenhagen F, Denmark

Address all correspondence and requests for reprints to: Bo Lumholtz, M.D., Department of Internal Medicine E, Frederiksberg Hospital, DK-2000 Copenhagen F, Denmark.

The effect of D,L-propranolol (80 mg daily) on the peripheral monodeiodination of rT₃, 3',5'-diiodothyronine (3',5'-T₂), 3,3'-diiodothyronine (3,3'-T₂), and 3'-monoiodothyronine (3'-T₁) was studied in seven out-patients with severe pretreatment hypothyroidism. The patients were maintained euthyroid on a constant L-T₄ replacement therapy. A bolus injection technique was used; MCR, production rate (PR), and conversion rate were determined using a noncompartmental kinetic model. During D,L-propranolol, serum rT₃ and 3',5'-T₂ increased (P < 0.02), and 3,3'-T₂ seemed to decrease. The MCRs of rT₃, 3',5'-T₂, and 3,3'-T₂ (P < 0.02) decreased during drug treatment. The MCR and PR of 3'-T₁ were reduced, albeit not significantly (P < 0.10). The PR of 3,3'-T₂ was reduced (P < 0.02), whereas the PRs of rT₃ and 3',5'-T₂ were unaltered. The conversion rate of rT₃ to 3',5'-T₂ was unaltered. No changes were seen in the apparent distribution volumes of the iodothyronines studied. The results are compatible with the assumption that D,L-propranolol, or a metabolite thereof, inhibits the 5'-deiodination of all of the iodothyronines. (J Clin Endocrinol Metab 54: 1097, 1982)

^* This work was supported by the Danish Hospital Foundation for Medical Research, Region of Copenhagen, the Farae Islands, and Greenland and The Danish Medical Research Council.

Received March 5, 1981.