Effect of parathyroid hormone on the determinants of glomerular filtration in dogs

Elevated levels of parathyroid hormone (PTH) often are associated with reduced glomerular filtration rate (GFR) in humans. Although PTH has been reported to reduce the ultrafiltration coefficient (Kf) in rats, GFR declined only if they were plasma expanded. In contrast, PTH does not reduce GFR in dogs, despite filtration pressure disequilibrium. To evaluate this apparent discrepancy, the determinants of GFR were measured in acutely thyroparathyroidectomized dogs. In the absence (n = 8) and presence (n = 10) of synthetic bovine PTH, GFR was 29 +/- 3 and 26 +/- 2 ml/min; Single nephron glomerular filtration rate was 58 +/- 4 and 51 +/- 3 nl/min; glomerular plasma flow was 248 +/- 22 and 250 +/- 24 nl/min; glomerular capillary pressure was 58 +/- 2 and 61 +/- 3 mmHg; Bowman's space pressure was 19 +/- 2 and 19 +/- 1 mmHg; and systemic oncotic pressure was 19 +/- 0.8 and 18 +/- 0.5 mmHg. Average effective filtration pressure (EFP) was significantly greater in the presence (18.6 +/- 1.3 mmHg) than in the absence (14.6 +/- 0.9 mmHg) of PTH. Therefore, Kf per glomerulus calculated from these data was significantly (P less than 0.01) less in the presence than in the absence of PTH (2.91 +/- 0.29 and 3.98 +/- 0.16 nl X min-1 X mmHg-1, respectively). It is concluded that PTH reduced Kf. Whereas this effect predicts reduced GFR in dogs, given filtration pressure disequilibrium, a concomitant increase in EFP maintained GFR in the present study.