Atrial natriuretic factor in untreated hyperthyroidism

Acute Experimental Hyperthyroidism Does Not Affect Basal and Volume-Induced Atrial Natriuretic Peptide Secretion in Healthy Subjects

Background. Excess circulating thyroid hormones are associated with increased cardiac atrial natriuretic peptide (ANP) secretion but the exact mechanisms involved have not been fully elucidated in vivo. Methods. To examine whether thyroid hormone regulation of ANP secretion is the result of a direct action on the myocardium and/or of an indirect action through alterations in the peripheral circulation, plasma ANP levels (baseline and volume expansion-induced) were evaluated in 14 healthy men, before and after triiodothyronine (T₃) administration. Results. T₃ administration was followed by a significant increase in serum T₃ levels and a significant decrease in serum TSH levels, without significantly affecting ANP levels. Systemic vascular resistance, plasma rennin activity (PRA), and aldosterone (ALDO) levels, as well as indices of left atrial function, were not significantly altered, despite a significant increase in cardiac output. Plasma volume expansion, induced by a 1500 ml normal saline (NSal) infusion, both before and after T₃ administration, was followed by a significant decrease in PRA and ALDO and a significant increase in plasma ANP levels, without significantly affecting the mean blood pressure (BP) and heart rate (HR) in each study period. The NSal-induced response, measured as the integrated area under the curve corrected for baseline values (-AUC), was not different after T₃ administration for ANP, ALDO, PRA, HR, and mean BP. Conclusion. In vivo thyroid hormone-induced myocardial ANP secretion is the result of an indirect action mainly through hemodynamic changes that increase atrial stretch.

Plasma atrial natriuretic hormone in hyperthyroidism

In 22 hyperthyroid patients, atrial natriuretic hormone (ANH) levels (71.91 +/- 21.03 pg/ml), measured during a 3-h-Holter, were found to be significantly higher (p < 0.001) than those in 20 age-matched normal subjects (37.22 +/- 8.73 pg/ml). We have demonstrated that the presence of tachiarrhythmias does not influence ANH release. The positive and significant correlation of FT3 with both ANH and heart rate confirms the hypothesis of a direct action of thyroid hormones on ANH release.