Effects of Variations in Thyroid Hormone Serum Concentrations on Serum ACE-Activity

Summary

Serum angiotensin converting enzyme activities were significantly increased in 26 untreated hyperthyroid patients (20.3 ± 5.4 U/ml; P < 0.001) compared with healthy control subjects (13.1 ± 2.3 U/ml). In 12 patients a significant fall in enzyme activities was observed after treatment compared with pretreatment serum ACE levels (P < 0.001). Eight patients with hypothyroidism (15.7 ± 5.1 U/ml) and 11 arthyreotic patients, totally thyroidectomized for well-differentiated thyroid cancer, showed no significant differences in serum ACE activities (14.3 ± 2.2 U/ml) compared with control subjects.

After thyroid hormone supplementation a significant increase in serum ACE activity (P < 0.05) was found in the athyreotic patients. Addition of increasing amounts of L-thyroxine to a serum sample of an athyreotic patient showed no significant effect on ACE activity in vitro. We suggest that the elevated serum ACE activity in hyper-thyroidism is not from the thyroid gland, but represents a direct effect of thyroid hormone on ACE synthesis and/or release from endothelial cells.

Key-Words:

Angiotensin-Converting Enzyme - Thyroid Gland - Hyperthyroidism - Hypothyroidism