Postnatal development of the renin-angiotensin system in thyroidectomized rats.

Postnatal changes in plasma renin activity (PRA), plasma renin concentration (PRC), plasma renin substrate (PRS) and plasma angiotensin II concentration (AII) were studied in young thyroidectomized rats from the 4th to the 10th week of life. Although there were no differences in the PRA pattern between thyroidectomized and euthyroid animals, an increase in PRC from the 6th week of life, together with a reduction of the glomerular filtration rate (GFR) and an increase in the fractional excretion of sodium (FENa) from the 8th week of life, was observed in young hypothyroid animals. Moreover, in thyroidectomized animals, PRS and AII declined until the 10th week of age, while in euthyroid animals an increase of PRS and AII was observed between the 8th and 10th weeks of life. These results show that the changes in sodium renal handling following thyroidectomy could have an influence on the RAS components.