Effects of parathyroid hormone on urinary acidification in the rat

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 +/- 0.33 in the control group (C) to 4.88 +/- 0.26 ml min-1 kg-1 in TPTX, while net acid excretion fell from 5.65 +/- 0.22 in C to 3.76 +/- 0.25 mumol min-1 kg-1 in TPTX. Kinetic data of urinary acidification obtained by microperfusion techniques in proximal tubules showed that the half-time of acidification (t/2) rose from 4.75 +/- 0.24 s in C to 8.97 +/- 0.64 s in TPTX and persisted elevated in TPTX + Ca2+ (7.40 +/- 0.43 s); in the latter group, stationary pH was not significantly different from that of the control group. Bicarbonate reabsorption (JHCO3) fell from 2.18 +/- 0.15 in C to 0.823 +/- 0.082 in TPTX and was 1.53 +/- 0.073 nmol s-1 cm-2 in TPTX + CA2+. These data suggest that normal pH gradients depend on normal calcium levels, but acidification half-times are dependent on PTH, which also contributes to keeping glomerular hemodynamics and acidification rates at normal levels.