Influence of parathyroid hormone on glomerular ultrafiltration in the rat

Experiments were performed on 22 plasma-expanded Munich-Wistar rats to investigated the effects of parathyroid hormone (PTH) on the determinants of glomerular ultrafiltration. Mean values for single nephron filtration rate (SNGFR), glomerular plasma flow rate (QA), systemic oncotic pressure, and transglomerular hydraulic pressure difference (deltaP) were similar in acutely thyroparathyroidectomized (TPTX) rats and non-TPTX rats. Nevertheless, the glomerular capillary ultrafiltration coefficient (Kf) was uniformly higher in TPTX rats (greater than 0.113 +/- 0.005 (SE) nl/(s.mmHg)] than in non-TPTX controls (0.088 +/- 0.005). In TPTX rats, infusion of a submaximal dose (1 U/kg per min) of PTH resulted in significant decreases in SNGFR at constant QA and deltaP, due primarily to return of Kf to non-TPTX levels. Infusion of 10 U/kg per min of PTH to non-TPTX rats further reduced Kf, on average to 0.042 +/- 0.001 nl/(s.mmHg), leading to further reduction in SNGFR, whereas QA and deltaP again remained constant. These findings suggest that PTH may play an important role in modulating Kf, and consequently, SNGFR.