[Altered alpha atrial natriuretic peptide (ANP) concentrations in plasma, atria and hypothalamus in experimentally...

In order to assess a possible involvement of thyroid hormone in atrial natriuretic peptide (ANP), experimentally induced hyper- and hypothyroid rats were employed, and the immunoreactive rat ANP (IR-ANP) concentrations in plasma, atria and brain regions including the hypothalamus were measured by a specific radioimmunoassay. Plasma IR-ANP concentration in hypothyroid rats was 14.5 +/- 2.9 (mean +/- SD) fmol/ml, significantly lower than that in control rats (p less than 0.05 vs control of 24.9 +/- 9.7 fmol/ml). Plasma IR-ANP concentration in hyperthyroid rats was 66.4 +/- 9.7 fmol/min, significantly higher than that in the controls (p less than 0.01). Atrial IR-ANP concentration in hyperthyroid rats was significantly lower than that in the controls (79.9 +/- 11.1 nmol/g vs 133.5 +/- 21.2 nmol/g (control), p less than 0.05), though no significant change was observed in atrial IR-ANP concentration in hypothyroid rats. While hypothalamic ANP concentration in hypothyroid rats was significantly lower than that in the controls (17.5 +/- 3.5 pmol/g vs 31.9 +/- 1.9 pmol/g (control), p less than 0.05), there was no significant change of that in the hyperthyroid rats. On reverse phase high performance liquid chromatography, the major peak in plasma and hypothalamus extract was thought to be identical to synthetic alpha-rat ANP (1-28). These results may suggest that in the hyperthyroid state an excessive amount of ANP is released from atria into the blood, and that in the central nervous system thyroid hormone involve ANP metabolism being different from the atrium.