The Effect of Adrenaline Pretreatment on the In Vitro Generation of 3,5,3′-Triiodothyronine and 3,3′,5′-Triiodothyronine (Reverse T₃) in Rat Liver Preparation

Summary

The effects of adrenaline (A) on liver T₃ and rT₃ neogenesis from T₄ were studied in Wistar rats. The animals were implanted subcutaneously either with A or placebo (P) especially coated tablets which linearly released the hormone. The serum A values 6 hrs after implantation of 7.5, 15.0 and 45.0 mg tablets were 6.5 ± 1.31, 6.8 ± 1.8 and 16.4 ± 1.9 ng/ml, respectively vs 4.4 ± 2.5 ng/ml seen in P pretreated group. The output rates of A were 0.11 (7.5 mg), 0.18 (15 mg) and 0.52 μg/ml (45 mg). The pretreatment with A led to hyperglycemia and the “low T₃ syndrome”. Neogenesis of T₃ from T₄ in medium containing liver microsomes of P pretreated rats was 5.49 ± 0.25 pmol of T₃/mg protein/min and decreased in A pretreated rats to 3.82 ± 0.17, 3.12 ± 0.27 and 3.06 ± 0.11 pmol of T₃/mg of protein/min. Neogenesis of rT₃ from T₄ in microsomes from P group was 1.52 ± 0.09 pmol rT₃/mg protein/min and increased after A to 2.71 ± 0.11, 2.60 ± 0.21 and 2.21 ± 0.34 pmol of rT₃/mg protein/min thus showing no dose dependency. Enrichment of microsomes medium with cytosol either from P or A pretreated rats had no effect on T₃ generation thus excluding effect of A on cytosolic cofactor. Although cytosol further increased rT₃ neogenesis this was seen regardless of whether cytosol was obtained from A or P implanted rats. It is concluded that A decreases the activity of T₄-5′-deiodinase in liver, and possibly increases the activity of T₄-5-deiodinase.

Key-Words:

Adrenaline - Thyroxine - Triiodothyronine - Reverse Triiodothyronine - Adrenaline Induced Changes in T₃ and rT₃ Neogenesis - T₄-5′-Deiodinase - T₄-5-Deiodinase