Parathyroid hormone and calcitriol in hypertension caused by dietary calcium deficiency in rats

Hypertension caused by calcium deficiency in the diet has been linked with an increase in parathyroid hormone (PTH) and calcitriol levels. We evaluate d arterial blood pressure (ABP), PTH, and calcitriol in normotensive Spragu e-Dawley rats (SDR) and in spontaneously hypertensive rats (SHR) fed from w eaning on a control diet with a normal calcium content (1%) or a low-calciu m diet (0.1%). The calcemia was also measured in the rats by colorimetric m ethods. The low-calcium diet decreased the calcemia in both strains and bro ught about an increase in the ABP which was significant in adult SDR and pa rticularly noticeable during the early hypertensive phase in SHR. The rats fed on this diet had higher hormonal plasma levels when compared with the c orresponding values in rats fed on the control diet. In particular, the SDR fed on the low-calcium diet showed much higher PTH(122.6 +/- 31.0 pg/ml, p less than or equal to 0.05) and calcitriol (458.0 +/- 13.1 pg/ml, p I 0.01 ) values than the SDR fed on the control diet (PTH 31.7 +/- 2.80 pg/ml; cal citriol 292.1 +/- 17.5 pg/ml). These endocrine alterations could justify th e increase in ABP caused by dietary calcium deficiency in normotensive rats . Nevertheless, the results of this study indicate that the modifications o f the ABP caused by the low-calcium diet in SHR could not be correlated wit h significant increases in these hormones.