Atrial natriuretic peptide and thyroid hormones' relation to plasma and heart calcium and magnesium concentrations of Wistar rats exposed to cold and hot ambients.

ABSTRACT

Plasma ANP (atrial natriuretic peptide), thyroid hormones, and calcium and magnesium levels as well as heart tissue calcium and magnesium concentrations were determined in male Wistar rats after exposure of 114 rats at low temperature (4 degrees C) and 95 rats at high temperature (35-36 degrees C) for 28 d. Plasma ANP, triiodothyronine (T3), thyroxine (T4), thyroid-stimulating hormone (TSH), free T3, and free T4 were estimated by radioimmunoassay, and plasma and heart tissue levels of Ca and Mg by flame atomic absorption spectrophotometry. Results were compared to a control group exposed at 20-22 degrees C (76 rats). All the above parameters in control rats did not show statistically significant variations during the study. A significant increase of plasma ANP, T3, T4, Ca, and Mg concentrations developed during cold exposure, whereas a gradual decrease of plasma ANP, T3, T4, and Mg concentrations was revealed during hot exposure. A significant increase of heart tissue Mg concentrations developed during hot exposure. Results also indicate that plasma ANP and T3 levels are proportionally related, whereas an inverse relationship exists between plasma ANP and T3 levels and heart Mg concentrations, in both cold and hot exposed rats. In conclusion, ANP and thyroid hormones in relation to Ca and Mg play an important role in temperature adaptation.