ABSTRACT
To evaluate the effects of parathyroid hormone (PTH) on urinary acidification parameters, thyroparathyroidectomy was performed in normal (TPTX) and in calcium-supplemented rats (TPTX+Ca2**). Both groups were supplemented with thyroxin. Glomerular filtration rate (GFR) fell from 7.79 ñ 0.33 in the control group (C) to 4.88 ñ 0.26 ml min**-1Kg**-1 in TPTX, while net acid excretion fell from 5.65 ñ 0.22 in C to 3.76 ñ 0.26 µmol min**1Kg in TPTX. Kinetic dat of urinary acidification obtained by microperfusion techniques in proximal tubules showed that the half-time of acidification (t/2) rose from 4.75 ñ 0.24 s in C to 8.97 ñ 0.64s in TPTX and persisted elevated in TPTx +Ca**2+ (7.40 ñ 0.43s); in the latter group, stationary pH was not significantly different from that of the control group. Bicarbonate reabsorption (J**HCO3) fell from 2.18 ñ 0.15 in C to 0.823 ñ 0.082 in TPTX and was 1.53 ñ 0.073 nmol s**-1 cm**-2 in TPTX+Ca**2+. These suggest that normal pH gradients depend on normal calcium levels, but acidification half-times are dependent on PTH, which also contributes keeping glomerular hemodynamics and acidification rates at normal levels