Thyroid Disorders Change the Pattern of Response of Angiotensinase Activities in the Hypothalamus-Pituitary-Adrenal Axis of Male Rats

Abstract

Thyroid disorders affect the hypothalamic-pituitary-adrenal axis with important consequences on the cardiovascular function in which the renin-angiotensin system plays a major role. Hypo and hyperthyroidism influence the classic main components of the renin-angiotensin system. However, the behavior of other elements of the renin-angiotensin system such as Ang III, Ang 2-10, Ang IV, or AT4, regulated by angiotensinase enzymes such as alanyl- (AlaAP), cystinyl- (CysAP), glutamyl- (GluAP), or aspartyl-aminopeptidase (AspAP), has not yet been described. In order to obtain a comprehensive view on the response of the renin-angiotensin system in the hypothalamic-pituitary-adrenal axis of animals with thyroid disorders, these enzyme activities were simultaneously analyzed fluorometrically, using arylamide derivatives as substrates in hypothalamus, anterior and posterior pituitary, adrenals and plasma of euthyroid, hypothyroid, and hyperthyroid rats, and their intra- and inter-tissue correlations were evaluated. The response is depending on the type of enzyme studied, its location and the thyroid status. Anterior pituitary, adrenals and plasma were mainly affected by the thyroid disorders. In the anterior pituitary, GluAP and AspAP increased in hypothyroid rats. In adrenals, AlaAP and CysAP decreased in hypothyroid whereas GluAP and AspAP decreased in hyperthyroid rats. In plasma, while AlaAP increased in hypo- and hyperthyroid rats, CysAP and GluAP decreased only in hyperthyroid. In comparison with euthyroid, intra-tissue correlations decreased in hypothyroid but inter-tissue correlations decreased mainly in hyperthyroid rats. Thyroid disorders also produced a disruption in the pattern of inter-tissue correlations observed in euthyroid. These results suggest that thyroid hormone levels hit components of the renin-angiotensin system and may influence the paracrine and endocrine cross talk between cells.