Atrial natriuretic peptide in hypothyroidism.

The effect of hypothyroidism on circulating levels of atrial natriuretic peptide (ANP) was studied in 11 hypothyroid patients (aged 11-65 yr; mean, 31 yr) and 13 normal subjects (aged 28-39 yr; mean, 32 yr). Plasma ANP was 32 +/- 9 (+/- SD) pg/ml in normal subjects and 20 +/- 5 pg/ml in the hypothyroid patients (P less than 0.005). In 7 hypothyroid patients, plasma ANP levels were measured after 10-14 weeks of L-T4 therapy. ANP increased from 22 +/- 5 to 46 +/- 18 pg/ml (P less than 0.02), along with an increase in mean serum T4 from 0.6 +/- 0.5 to 8.1 +/- 2.5 micrograms/dl (P less than 0.001). Thus, hypothyroidism is characterized by decreased circulating levels of ANP which are reversed by L-T4 therapy.