Influence of thyroid disorders on the kidney expression and plasma activity of aminopeptidase A.

Abstract

OBJECTIVE: Thyroid disorders may affect blood pressure and renal function modifying factors of the plasmatic and kidney renin-angiotensin system such as aminopeptidase A (AP A) that metabolizes angiotensin II to angiotensin III. We investigated the expression of AP A in the kidney, as well as its enzymatic activity in the plasma of euthyroid, hyperthyroid, and hypothyroid adult male rats. METHODS: Hyperthyroidism was induced by daily subcutaneous injections of tetraiodothyronine. Hypothyroid rats were obtained by administration of methimazole in drinking water. Expression of AP A was determined by Western blot analysis. Plasma AP A activity was measured fluorometrically using glutamyl-β-naphthylamide as substrate. RESULTS: While hyperthyroid rats exhibited lower levels of plasma AP A activity than controls, the kidney of hyperthyroid animals expressed significantly higher AP A than controls and hypothyroid animals. CONCLUSIONS: A discrepancy between the high expression of AP A in kidney of hyperthyroid rats and the low activity of AP A measured in plasma and kidney of hyperthyroid animals was found. The posttranslational influence of environmental biochemical factors may be in part responsible for that divergence.