Atrial angiotensinase activity in hypothyroid, euthyroid, and hyperthyroid rats.

Area of Science:

• Endocrinology
• Cardiovascular Physiology
• Biochemistry

Background:

• Thyroid dysfunction profoundly impacts cardiovascular function.
• Thyroid hormones influence the cardiac renin-angiotensin system (RAS).
• Aminopeptidases (angiotensinases) regulate angiotensin peptide metabolism.

Purpose of the Study:

• To investigate the relationship between thyroid status and atrial angiotensinase activity.
• To determine how hypothyroidism and hyperthyroidism affect specific aminopeptidase activities in rat atria.

Main Methods:

• Adult male rats were made hypothyroid (methimazole) or hyperthyroid (thyroxine).
• Soluble and membrane-bound aminopeptidase activities (alanyl, glutamyl, aspartyl) were measured fluorometrically in atrial tissue.
• Enzyme activities were correlated with thyroid status (hypothyroid, euthyroid, hyperthyroid).

Main Results:

• Both hypo- and hyperthyroidism significantly increased soluble aspartyl aminopeptidase activity by 50% in rat atria.
• Hyperthyroidism (thyroxine treatment) increased membrane-bound alanyl aminopeptidase (37%) and aspartyl aminopeptidase (30%) activities.
• These changes suggest altered metabolism of angiotensin peptides, specifically increased des-Asp Ang I formation and Ang III to Ang IV conversion.

Conclusions:

• Thyroid dysfunction alters atrial angiotensinase activities, impacting local cardiac RAS.
• Increased soluble aspartyl aminopeptidase in both conditions and increased membrane-bound activities in hyperthyroidism suggest significant peptide processing changes.
• Findings support the role of altered cardiac RAS in cardiovascular alterations associated with thyroid dysfunction.